{{short description|Photosynthetic part of a vascular plant}} {{Redirect|Leaves|other uses of "leaf" or "leaves"|Leaf (disambiguation)}} {{Redirect-distinguish|Foliage|Autumn foliage}} {{pp-move}} {{Use American English|date=June 2025}} {{Use mdy dates|date=June 2025}} [[File:Leaf Varieties (15 sp).png|thumb|The diversity of leaves, including ''[[Bismarckia]]'', ''[[Araucaria]]'', ''[[Euphorbia]]'', ''[[Nymphaea]]'', ''[[Colocasia]]'', [[Hildegardia (plant)|''Hildegardia'']], ''[[Picea]]'', ''[[Melocactus]]'', ''[[Cycas]]'', [[Acer (genus)|''Acer'']], ''[[Yucca]]'', ''[[Ferocactus]]'', and ''[[Ocimum]]''.|401x401px]] [[File:Lisc lipy.jpg|thumb|Leaf of ''[[Tilia tomentosa]]'' (silver linden tree)]] [[File:Leaf, Bud, and Stem Diagram.svg|thumb|Diagram of a simple leaf. {{flatlist|{{ordered list | Apex | Midvein (Primary vein) | Secondary vein | Lamina | Leaf margin | Petiole | Bud | Stem }}}}]] [[File:Diagramed parts of leaves.svg|thumb|Top and right: staghorn sumac, ''[[Rhus typhina]]'' (compound leaf) <br/>Bottom: skunk cabbage, ''[[Symplocarpus foetidus]]'' (simple leaf) {{olist |Apex |Primary vein |Secondary vein |Lamina |Leaf margin |Rachis}}]]
A '''leaf''' ({{plural form}}: '''leaves''') is a principal appendage of the [[plant stem|stem]] of a [[vascular plant]],{{sfn|Esau|2006}} usually borne laterally above ground and specialized for [[photosynthesis]]. Leaves are collectively called '''foliage''', as in "autumn foliage",{{sfn|Haupt|1953}}{{sfn|Mauseth|2009}} while the leaves, stem, [[flower]], and [[fruit]] collectively form the [[Shoot (botany)|shoot]] system.<ref>{{Cite web |url=https://www.cactus-art.biz/note-book/Dictionary/Dictionary_S/dictionary_shoot_system.htm |title=Shoot system |date=n.d. |website=Dictionary of botanic terminology |publisher=Cactus Art Nursery |access-date=May 4, 2021 |archive-date=May 4, 2021 |archive-url=https://web.archive.org/web/20210504055224/https://www.cactus-art.biz/note-book/Dictionary/Dictionary_S/dictionary_shoot_system.htm |url-status=live}}</ref> In most leaves, the primary [[Photosynthesis|photosynthetic]] [[Tissue (biology)|tissue]] is the [[palisade mesophyll]] and is located on the upper side of the blade or lamina of the leaf,{{sfn|Esau|2006}} but in some species, including the mature foliage of ''[[Eucalyptus]]'',{{sfn|James et al|1999}} palisade mesophyll is present on both sides and the leaves are said to be isobilateral. The leaf is an integral part of the stem system, and most leaves are flattened and have distinct upper ([[Glossary of botanical terms#adaxial|adaxial]]) and lower ([[Glossary of botanical terms#abaxial|abaxial]]) surfaces that differ in color, [[Trichome|hairiness]], the number of [[stomata]] (pores that intake and output gases), the amount and structure of [[epicuticular wax]], and other features. Leaves are mostly green in color due to the presence of a compound called [[chlorophyll]], which is essential for photosynthesis as it absorbs light energy from the [[Sun]]. A leaf with lighter-colored or white patches or edges is called a [[Variegation|variegated leaf]].
Leaves vary in shape, size, texture and color, depending on the species. The broad, flat leaves with complex [[#Venation|venation]] of [[flowering plant]]s are known as ''megaphylls'' and the species that bear them (the majority) as broad-leaved or [[euphyllophyte|megaphyllous]] plants, which also include [[acrogymnosperm]]s and [[fern]]s. In the [[lycopods]], with different evolutionary origins, the leaves are simple (with only a single vein) and are known as ''microphylls''.{{sfn|Stewart|Rothwell|1993}} Some leaves, such as [[bulb]] scales, are not above ground. In many aquatic species, the leaves are submerged in water. [[Succulent plant|Succulent]] plants often have thick juicy leaves, but some leaves are without major photosynthetic function and may be dead at maturity, as in some [[cataphyll]]s and [[Thorns, spines, and prickles|spines]]. Furthermore, several kinds of leaf-like structures found in vascular plants are not totally homologous with them. Examples include flattened plant stems called [[phylloclade]]s and [[wikt:cladode|cladodes]], and flattened leaf stems called [[Petiole (botany)|phyllodes]] that differ from leaves both in their structure and origin.{{sfn|Mauseth|2009}}{{sfn|Cooney-Sovetts|Sattler|1987}} Some structures of non-vascular plants look and function much like leaves. Examples include the [[Glossary of botanical terms#phyllid|phyllids]] of [[mosses]] and [[liverworts]].
==General characteristics== [[File:3D rendering of a micro CT scan of a piece of dried leaf..ogv|thumb|3D rendering of a [[computed tomography]] scan of a leaf]]
Leaves are the most important organs of most [[vascular plant]]s.{{sfn|Tsukaya|2013}} Green plants are [[autotroph]]ic, meaning that they do not obtain food from other living things but instead create their own food by [[photosynthesis]]. They capture the energy in [[sunlight]] and use it to make simple [[sugar]]s, such as [[glucose]] and [[sucrose]], from [[carbon dioxide]] ({{CO2}}) and water. The sugars are then stored as [[starch]], further processed by [[chemical synthesis]] into more complex organic molecules such as [[protein]]s or [[cellulose]], the basic structural material in plant cell walls, or [[Metabolism|metabolized]] by [[cellular respiration]] to provide chemical energy to run cellular processes. The leaves draw water from the ground in the [[transpiration stream]] through a [[Vascular tissue|vascular conducting system]] known as [[xylem]] and obtain carbon dioxide from the [[atmosphere]] by diffusion through openings called [[stomata]] in the outer covering layer of the leaf ([[Epidermis (botany)|epidermis]]), while leaves are orientated to maximize their exposure to sunlight. Once sugar has been synthesized, it needs to be transported to areas of active growth such as the [[Shoot (botany)|shoots]] and [[root]]s. Vascular plants transport sucrose in a special tissue called the [[phloem]]. The phloem and xylem are parallel to each other, but the transport of materials is usually in opposite directions. Within the leaf these vascular systems branch (ramify) to form veins that supply as much of the leaf as possible, ensuring that [[cell (biology)|cells]] carrying out photosynthesis are close to the transportation system.{{sfn|Feugier|2006}}
Typically leaves are broad, flat and thin (dorsiventrally flattened), thereby maximizing the surface area directly exposed to light and enabling the light to penetrate the [[Plant cell#Types of plant cells and tissues|tissues]] and reach the [[chloroplast]]s, thus promoting photosynthesis. They are arranged on the plant so as to expose their surfaces to light as efficiently as possible without shading each other, but there are many exceptions and complications. For instance, plants adapted to windy conditions may have [[pendent]] leaves, such as in many [[willow]]s and [[eucalypt]]s. The flat, or laminar, shape also maximizes [[thermal conduction|thermal contact]] with the surrounding air, promoting cooling. Functionally, in addition to carrying out photosynthesis, the leaf is the principal site of [[transpiration]], providing the energy required to draw the transpiration stream up from the roots, and [[guttation]].
Many [[conifer]]s have thin needle-like or scale-like leaves that can be advantageous in cold climates with frequent snow and frost.{{sfn|Purcell|2016}} These are interpreted as reduced from [[Microphylls and megaphylls|megaphyllous]] leaves of their [[Devonian]] ancestors.{{sfn|Stewart|Rothwell|1993}} Some leaf forms are adapted to modulate the amount of light they absorb to avoid or mitigate excessive heat, [[ultraviolet]] damage, or desiccation, or to sacrifice light-absorption efficiency in favor of protection from herbivory. For [[xerophyte]]s the major constraint is not light [[Radiant flux|flux]] or [[irradiance|intensity]], but drought.{{sfn|Willert et al|1992}} Some [[leaf window|window plants]] such as ''[[Fenestraria]]'' species and some ''[[Haworthia]]'' species such as ''Haworthia tesselata'' and ''[[Haworthia truncata]]'' are examples of xerophytes.{{sfn|Bayer|1982}}
Leaves function to store chemical energy and water (especially in [[succulents]]) and may become specialized organs serving other functions, such as [[tendril]]s of [[pea]]s and other [[legume]]s, the protective [[Thorns, spines, and prickles|spines]] of [[Cactus|cacti]], and the insect traps in [[carnivorous plant]]s such as ''[[Nepenthes]]'' and ''[[Sarracenia]]''.{{sfn|Simpson|2011|loc=p. 356}} Leaves are the fundamental structural units from which [[Conifer cone|cones]] are constructed in [[gymnosperm]]s (each cone scale is a modified megaphyll leaf known as a [[sporophyll]]){{sfn|Stewart|Rothwell|1993}}{{rp|408}} and from which flowers are constructed in [[flowering plant]]s.{{sfn|Stewart|Rothwell|1993}}{{rp|445}} [[File:Vein skeleton of a leaf (de-ghosted).jpg|thumb|Vein skeleton of a leaf. Veins contain [[lignin]] that make them harder to degrade for microorganisms.]]
The internal organization of most kinds of leaves has evolved to maximize exposure of the photosynthetic [[organelles]] ([[chloroplast]]s) to light and to increase the absorption of {{CO2}} while at the same time controlling water loss. Their surfaces are waterproofed by the [[plant cuticle]], and gas exchange between the mesophyll cells and the atmosphere is controlled by minute (length and width measured in tens of μm) stomata that open or close to regulate the rate exchange of {{CO2}}, [[oxygen]] (O<sub>2</sub>), and [[water vapor]] into and out of the internal intercellular space system. Stomatal opening is controlled by the [[turgor pressure]] in a pair of [[guard cell]]s that surround the stomatal aperture. In any square centimeter of a plant leaf, there may be from 1,000 to 100,000 stomata.{{sfn|Krogh|2010}} [[File:Layers of a Leaf.svg|thumb|This is a cross section showing the different layers of a leaf. 1 - Upper epidermis 2 - [[Palisade mesophyll]] 3 - Spongy mesophyll 4 - Vein 5 - [[Xylem]] 6 - [[Phloem]] 7 - [[Collenchyma]] 8 - [[Chloroplasts]] 9 - [[Cell nucleus|Nucleus]] 10 - [[Vacuole]] 11 - [[Stomata]] 12 - [[Cuticle]]]] [[File:Eucalyptus foliage isobilateral dorsiventral IMG 0588e.JPG|thumb|Near the ground these ''Eucalyptus'' saplings have juvenile dorsiventral foliage from the previous year, but this season their newly sprouting foliage is isobilateral, like the mature foliage on the adult trees above.]]
The shape and structure of leaves vary considerably from species to species of plant, depending largely on their adaptation to climate and available light, but also to other factors such as grazing animals, available nutrients, and ecological competition from other plants. Considerable changes in leaf type occur within species, too, for example as a plant matures (''Eucalyptus'' species commonly have isobilateral, pendent leaves when mature and dominating their neighbors; however, such trees tend to have erect or horizontal [[dorsiventral]] leaves as seedlings, when their growth is limited by the available light.){{sfn|James |Bell|2000}} Other factors include the need to balance water loss at high temperature and low humidity against the need to absorb {{CO2}}. In most plants, leaves also are the primary organs responsible for [[transpiration]] and [[guttation]] (beads of fluid forming at leaf margins).
Leaves can also store food and water and are modified accordingly to meet these functions, for example in the leaves of succulent plants and in [[bulb]] scales. The concentration of photosynthetic structures in leaves requires that they be richer in [[protein]], [[mineral]]s, and sugars than, say, woody stem tissues. Accordingly, leaves are prominent in the [[diet (nutrition)|diet]] of many [[animal]]s. Correspondingly, leaves represent heavy investment on the part of the plants bearing them, and their retention or disposition are the subject of elaborate strategies for dealing with pest pressures, seasonal conditions, and protective measures such as the growth of thorns and the production of [[phytolith]]s, [[lignin]]s, [[tannin]]s and [[poison]]s.
[[Deciduous]] plants in cold temperate regions typically shed their leaves in [[autumn]], whereas in areas with a severe [[dry season]], some plants may shed their leaves until the dry season ends. In either case, the shed leaves often contribute their retained nutrients to the soil where they fall. In contrast, many other non-seasonal plants, such as [[Arecaceae|palms]] and conifers, retain their leaves for long periods; ''[[Welwitschia]]'' retains its two main leaves throughout a lifetime that may exceed a thousand years.
The leaf-like organs of [[bryophyte]]s (e.g., [[moss]]es and [[Marchantiophyta|liverworts]]), known as [[Glossary of botanical terms#phyllid|phyllids]], differ greatly morphologically from the leaves of [[vascular plants]]. In most cases, they lack vascular tissue, are a single cell thick and have no [[plant cuticle|cuticle]], stomata, or internal system of intercellular spaces. (The phyllids of the moss family [[Polytrichaceae]] are notable exceptions.) The phyllids of bryophytes are only present on the [[gametophyte]]s, while in contrast the leaves of vascular plants are only present on the [[sporophytes]]. These can further develop into either vegetative or reproductive structures.{{sfn|Simpson|2011|loc=p. 356}}
Simple, vascularized leaves ([[microphylls]]), such as those of the early Devonian lycopsid ''[[Baragwanathia]]'', first evolved as enations, extensions of the stem. True leaves or euphylls of larger size and with more complex venation did not become widespread in other groups until the Devonian period, by which time the carbon dioxide concentration in the atmosphere had dropped significantly. This occurred independently in several separate lineages of vascular plants, in [[progymnosperm]]s like ''[[Archaeopteris]]'', in [[Sphenopsida]], [[fern]]s and later in the [[gymnosperm]]s and [[angiosperm]]s. Euphylls are also referred to as macrophylls or megaphylls (large leaves).{{sfn|Stewart|Rothwell|1993}}
== Morphology == {{see also|Glossary of leaf morphology}} [[File:Travel Deep Inside a Leaf - Annotated Version - California Academy of Sciences.webm|thumb|Animated zoom into the leaf of a ''[[Sequoia sempervirens]]'' (California redwood)]] [[File:Rosa canina blatt 2005.05.26 11.50.13.jpg|thumb|upright|''[[Rosa canina]]'': [[Petiole (botany)|Petiole]], two [[stipules]], [[rachis]], five [[leaflet (botany)|leaflets]]|alt=Leafstem of dog rose with petiole, stipules and leaflets ]] [[File:Citrus leaf(crop).jpg|thumb|upright|''[[Citrus]]'' leaves with translucent glands{{sfn|Heywood et al|2007}}]]
A structurally complete leaf of an [[angiosperm]] consists of a [[petiole (botany)|petiole]] (leaf stalk, called a [[stipe (botany)|stipe]] in ferns), a lamina (leaf blade), [[stipule]]s (small structures located to either side of the base of the petiole) and a sheath. Not every species produces leaves with all of these structural components. The lamina is the expanded, flat component of the leaf that contains the [[chloroplasts]]. The sheath is a structure at the base that fully or partially wraps around the [[plant stem|stem]], above the node where the leaf is attached. Leaf sheathes typically occur in [[Poaceae]] (grasses), [[Apiaceae]] (umbellifers), and many palms. Between the sheath and the lamina, there may be a [[pseudopetiole]], a petiole like structure. Pseudopetioles occur in some [[monocotyledons]] including [[bananas]], [[Arecaceae|palms]] and [[bamboos]].{{sfn|Simpson|2011|loc=pp. 356–357}} Stipules may be conspicuous (e.g. [[beans]] and [[roses]]), soon falling or otherwise not obvious as in [[Moraceae]] or absent altogether as in the [[Magnoliaceae]]. A petiole may be absent (apetiolate), or the blade may not be laminar (flattened). The petiole mechanically links the leaf to the plant and provides the route for transfer of water and sugars to and from the leaf. The lamina is typically the location of the majority of photosynthesis. The upper ([[Glossary of botanical terms#A|adaxial]]) angle between a leaf and a stem is known as the '''axil''' of the leaf. It is often the location of a [[bud]]. Structures located there are called "axillary".
[[File:Fulles noves, magraner (partida de la Belenguera, Alginet, País Valencià).jpg|thumb|New [[pomegranate]] leaves]]
External leaf characteristics, such as shape, margin, hairs, the petiole, and the presence of stipules and glands, are frequently important for identifying plants to family, genus or [[species]] levels, and botanists have developed a rich [[terminology]] for describing leaf characteristics. Leaves almost always have determinate growth. They grow to a specific pattern and shape and then stop. Other plant parts like stems or roots have non-determinate growth, and usually continue to grow as long as they have the resources to do so.
[[File:Eenbruinigherfstblad.jpg|thumb|A leaf shed in [[autumn]]]]
The type of leaf is usually characteristic of a species (monomorphic), although some species produce more than one type of leaf (dimorphic or [[Polymorphism (biology)|polymorphic]]). The longest leaves are those of the [[Raffia palm]] (''Raphia regalis''), which may be up to {{cvt|25|m|ft}} long and {{convert|3|m|ft|abbr=on}} wide.{{sfn|Hallé|1977}} The terminology associated with the description of leaf morphology is presented, in illustrated form, at [[:wikibooks:Botany/Leaves (forms)|Wikibooks]].
[[File:Crossyne guttata IMG 2410c.jpg|thumb|150px|Prostrate leaves in ''[[Crossyne guttata]]'']]
Where leaves are basal, and lie on the ground, they are referred to as [[Glossary of plant morphology#prostrate|prostrate]].
{{anchor|Basic leaf types}} ===Basic leaf types=== [[File:Lilium superbum (Lithographie, Pierre-Joseph Redoute).jpg|thumb|upright|Whorled leaf pattern of the [[American tiger lily]]]]
[[Perennial]] plants whose leaves are shed annually are said to have deciduous leaves, while leaves that remain through winter are [[evergreen]]s. Leaves attached to stems by stalks (known as [[Petiole (botany)|petioles]]) are called petiolate, and if attached directly to the stem with no petiole they are called sessile.<ref name=types>{{cite book |title=Botany Illustrated: Introduction to Plants Major Groups Flowering Plant Families |publisher=Thomson Science |date=1984 |page=21}}</ref>
* Ferns have [[frond]]s. * Conifer leaves are typically needle- or awl-shaped or scale-like; they are usually evergreen but can sometimes be deciduous. Usually, they have a single vein. * The standard form of flowering plants (angiosperm) includes [[stipule]]s, a petiole, and a [[glossary of botanical terms#lamina|lamina]]. * [[Lycophyte]]s have [[microphylls and megaphylls|microphylls]]. * [[Monocotyledon#Leaves|Sheath]] leaves are the type found in most [[Poaceae|grasses]] and many other monocots. * Other specialized leaves include those of ''[[Nepenthes]]'', a pitcher plant.
[[Dicotyledon|Dicot]] leaves have blades with pinnate venation (where major veins diverge from one large mid-vein and have smaller connecting networks between them). Less commonly, dicot leaf blades may have palmate venation (several large veins diverging from [[Petiole (botany)|petiole]] to leaf edges). Finally, some exhibit parallel venation.<ref name=types/> [[Monocotyledon|Monocot]] leaves in temperate climates usually have narrow blades and usually parallel venation converging at leaf tips or edges. Some also have pinnate venation.<ref name="types" />
===Arrangement on the stem=== {{main|Phyllotaxis}} The arrangement of leaves on the stem is known as [[phyllotaxis]].<ref>Didier Reinhardt and Cris Kuhlemeier, "Phyllotaxis in higher plants", in Michael T. McManus, Bruce Veit, eds., ''Meristematic Tissues in Plant Growth and Development'', January 2002, {{ISBN|978-1-84127-227-6}}, Wiley-Blackwell.</ref> A large variety of phyllotactic patterns occur in nature:
[[File:Leaves opposite.jpg|thumb|upright|The leaves on this plant are arranged in pairs [[opposite leaves|opposite]] one another, with successive pairs at right angles to each other (''decussate'') along the red stem. Note the developing buds in the axils of these leaves.]] [[File:Senecio angulatus 005.jpg|thumb|upright|The leaves on this plant (''[[Senecio angulatus]]'') are alternately arranged.]]
;Alternate: One leaf, branch, or flower part attaches at each point or node on the stem, and leaves alternate direction—to a greater or lesser degree—along the stem. ;Basal: Arising from the base of the plant. ;Cauline: Attached to the aerial stem. ;Opposite: Two leaves, branches, or flower parts attach at each point or node on the stem. Leaf attachments are paired at each node. ;[[Decussate]]: An opposite arrangement in which each successive pair is rotated 90° from the previous. ;[[Whorl (botany)|Whorled]], or verticillate: Three or more leaves, branches, or flower parts attach at each point or node on the stem. As with opposite leaves, successive whorls may or may not be decussate, rotated by half the angle between the leaves in the whorl (i.e., successive whorls of three rotated 60°, whorls of four rotated 45°, etc.). Opposite leaves may appear whorled near the tip of the stem. '''Pseudoverticillate''' describes an arrangement only appearing whorled, but not actually so. ;Rosulate: Leaves form a [[rosette (botany)|rosette]]. ;Rows: The term ''distichous'' literally means ''two rows''. Leaves in this arrangement may be alternate or opposite in their attachment. The term ''2-ranked'' is equivalent. The terms ''tristichous'' and ''tetrastichous'' are sometimes encountered. For example, the "leaves" (actually microphylls) of most species of ''[[Selaginella]]'' are tetrastichous but not decussate.
In the simplest mathematical models of phyllotaxis, the apex of the stem is represented as a circle. Each new node is formed at the apex, and it is rotated by a constant angle from the previous node. This angle is called the ''divergence angle''. The number of leaves that grow from a node depends on the plant species. When a single leaf grows from each node, and when the stem is held straight, the leaves form a [[helix]].
The divergence angle is often represented as a fraction of a full rotation around the stem. A rotation fraction of 1/2 (a divergence angle of 180°) produces an alternate arrangement, such as in [[Gasteria]] or the fan-aloe [[Kumara plicatilis]]. Rotation fractions of 1/3 (divergence angles of 120°) occur in [[beech]] and [[hazel]]. [[Oak]] and [[apricot]] rotate by 2/5, sunflowers, poplar, and pear by 3/8, and in willow and almond the fraction is 5/13.<ref>{{Cite book |title=Introduction to geometry |first=H. S. M. |last=Coxeter |name-list-style=vanc |author-link=Harold Scott MacDonald Coxeter |publisher=Wiley |year=1961 |page=169}}</ref> These arrangements are periodic. The [[denominator]] of the rotation fraction indicates the number of leaves in one period, while the [[numerator]] indicates the number of complete turns or ''gyres'' made in one period. For example: * 180° (or {{frac|1|2}}): two leaves in one circle (alternate leaves) * 120° (or {{frac|1|3}}): three leaves in one circle * 144° (or {{frac|2|5}}): five leaves in two gyres * 135° (or {{frac|3|8}}): eight leaves in three gyres.
Most divergence angles are related to the sequence of [[Fibonacci numbers]] {{math|''F''<sub>''n''</sub>}}. This sequence begins 1, 1, 2, 3, 5, 8, 13; each term is the sum of the previous two. Rotation fractions are often quotients {{math|''F''<sub>''n''</sub> / ''F''<sub>''n'' + 2</sub>}} of a Fibonacci number by the number two terms later in the sequence. This is the case for the fractions 1/2, 1/3, 2/5, 3/8, and 5/13. The ratio between successive Fibonacci numbers tends to the [[golden ratio]] {{math|φ {{=}} (1 + √5)/2}}. When a circle is divided into two arcs whose lengths are in the ratio {{math|1:φ}}, the angle formed by the smaller arc is the [[golden angle]], which is {{math|1/φ<sup>2</sup> × 360° ≈ 137.5°}}. Because of this, many divergence angles are approximately {{math|137.5°}}. In plants where a pair of opposite leaves grows from each node, the leaves form a double helix. If the nodes do not rotate (a rotation fraction of zero and a divergence angle of 0°), the two helices become a pair of parallel lines, creating a distichous arrangement as in [[maple]] or [[olive]] trees. More common in a decussate pattern, in which each node rotates by 1/4 (90°) as in the herb [[basil]]. The leaves of tricussate plants such as [[Nerium oleander]] form a triple helix. The leaves of some plants do not form helices. In some plants, the divergence angle changes as the plant grows.<ref>Reinhardt and Kuhlemeier, p. 175</ref> In orixate phyllotaxis, named after ''[[Orixa japonica]]'', the divergence angle is not constant. Instead, it is periodic and follows the sequence 180°, 90°, 180°, 270°.<ref>{{Cite journal |last1=Yonekura |first1=Takaaki |last2=Iwamoto |first2=Akitoshi |last3=Fujita |first3=Hironori |last4=Sugiyama |first4=Munetaka |date=June 6, 2019 |editor-last=Umulis |editor-first=David |title=Mathematical model studies of the comprehensive generation of major and minor phyllotactic patterns in plants with a predominant focus on orixate phyllotaxis |journal=PLOS Computational Biology |language=en |volume=15 |issue=6 |article-number=e1007044 |doi=10.1371/journal.pcbi.1007044 |issn=1553-7358 |pmc=6553687 |pmid=31170142 |doi-access=free |bibcode=2019PLSCB..15E7044Y}}</ref>
{{anchor|Divisions of the lamina (blade)}} ===Divisions of the blade=== [[File:Leaf 1 web.jpg|thumb|A leaf with laminar structure and [[pinnate]] venation]]
Two basic forms of leaves can be described considering the way the blade (lamina) is divided. A '''simple leaf''' has an undivided blade. However, the leaf may be ''dissected'' to form lobes, but the gaps between lobes do not reach to the main vein. A '''compound leaf''' has a fully subdivided blade, each [[leaflet (botany)|leaflet]] of the blade being separated along a main or secondary vein. The leaflets may have petiolules and stipels, the equivalents of the petioles and stipules of leaves. Because each leaflet can appear to be a simple leaf, it is important to recognize where the petiole occurs to identify a compound leaf. Compound leaves are a characteristic of some families of higher plants, such as the [[Fabaceae]]. The middle vein of a compound leaf or a [[frond]], when it is present, is called a [[rachis]].
;Palmately compound: The leaflets all have a common point of attachment at the end of the petiole, radiating like fingers of a hand; for example, ''[[Cannabis]]'' (hemp) and ''[[Aesculus]]'' (buckeyes).
;Pinnately compound: Leaflets are arranged either side of the main axis, or [[rachis]].{{glossary}}{{term|Odd pinnate}}{{defn|With a terminal leaflet; for example, ''[[ash tree|Fraxinus]]'' (ash).}}{{term|Even pinnate}}{{defn|Lacking a terminal leaflet; for example, ''[[Swietenia]]'' (mahogany). A specific type of even pinnate is [[Glossary of leaf morphology#bifoliolate|bifoliolate]], where leaves only consist of two leaflets; for example, ''[[Hymenaea]]''.}}{{glossary end}}
;Bipinnately compound: Leaves are twice divided: the leaflets (technically "[[wikt:subleaflet|subleaflets]]") are arranged along a secondary axis that is one of several branching off the rachis. Each leaflet is called a ''pinnule''. The group of pinnules on each secondary vein forms a ''pinna''; for example, ''[[Albizia]]'' (silk tree).
;Trifoliate (or trifoliolate): A pinnate leaf with just three leaflets; for example, ''[[clover|Trifolium]]'' (clover), ''[[Laburnum]]'' (laburnum), and some species of ''[[Toxicodendron]]'' (for instance, [[Toxicodendron radicans|poison ivy]]).
;Pinnatifid: Pinnately dissected to the central vein, but with the leaflets not entirely separate; for example, ''[[Polypodium]]'', some ''[[Sorbus]]'' (whitebeams). In pinnately veined leaves the central vein is known as the ''midrib''.
===Characteristics of the petiole=== [[File:Rabarber stelen.jpg|thumb|The overgrown petioles of [[rhubarb]] (''Rheum rhabarbarum'') are edible.]]
Leaves that have a petiole (leaf stalk) are said to be ''petiolate''. [[Sessility (botany)|Sessile]] (epetiolate) leaves have no petiole, and the blade attaches directly to the stem. Subpetiolate leaves are nearly petiolate or have an extremely short petiole and may appear to be sessile. In '''clasping''' or [[decurrent]] leaves, the blade partially surrounds the stem. When the leaf base completely surrounds the stem, the leaves are said to be '''perfoliate''', such as in ''[[Eupatorium perfoliatum]]''. In peltate leaves, the petiole attaches to the blade inside the blade margin. In some ''[[Acacia]]'' species, such as the koa tree (''[[Acacia koa]]''), the petioles are expanded or broadened and function like leaf blades; these are called [[phyllode]]s. There may or may not be normal pinnate leaves at the tip of the phyllode. A [[stipule]], present on the leaves of many [[dicotyledon]]s, is an appendage on each side at the base of the petiole, resembling a small leaf. Stipules may be lasting and not be shed (a stipulate leaf, such as in [[rose]]s and [[bean]]s), or be shed as the leaf expands, leaving a stipule scar on the twig (an exstipulate leaf). The situation, arrangement, and structure of the stipules is called the "stipulation". ;Free, lateral: As in ''[[Hibiscus]]''. ;Adnate: Fused to the petiole base, as in ''[[Rose|Rosa]]''. ;Ochreate: Provided with [[ochrea]], or sheath-formed stipules, as in [[Polygonaceae]]; e.g., [[rhubarb]]. ;Encircling the petiole base:{{glossary}}{{term|[[wikt:interpetiolar stipule|Interpetiolar]]}}{{defn|Between the petioles of two opposite leaves, as in [[Rubiaceae]].}}{{term|[[wikt:intrapetiolar stipule|Intrapetiolar]]}}{{defn|Between the petiole and the subtending stem, as in [[Malpighiaceae]].}}{{glossary end}}
===Veins=== {{see also|#Venation|#Vascular tissue}} [[File:Taro leaf underside, backlit by sun.jpg|thumb|Branching veins on underside of [[taro]] leaf]] [[File:Tilia x cordata flower veination.JPG|thumb|The venation within the bract of a [[Tilia|linden]]]] [[File:Leaf Skeleton negative (like photogram).jpg|upright|thumb|[[Micrograph]] of a leaf skeleton]]
Veins (sometimes referred to as nerves) constitute one of the most visible features of leaves. The veins in a leaf represent the vascular structure of the organ, extending into the leaf via the petiole and providing transportation of water and nutrients between leaf and stem, and play a crucial role in the maintenance of leaf water status and photosynthetic capacity. They also play a role in the mechanical support of the leaf.{{sfn|Rolland-Lagan et al|2009}}{{sfn|Walls|2011}} Within the lamina of the leaf, while some vascular plants possess only a single vein, in most this vasculature generally divides (ramifies) according to a variety of patterns (venation) and form cylindrical bundles, usually lying in the median plane of the [[#Mesophyll|mesophyll]], between the two layers of [[#Epidermis|epidermis]].{{sfn|Dickison|2000}} This pattern is often specific to taxa, and of which angiosperms possess two main types, [[Parallel (geometry)|parallel]] and [[#Venation|reticulate]] (net like). In general, parallel venation is typical of monocots, while reticulate is more typical of [[eudicots]] and [[magnoliids]] ("dicots"), though there are many exceptions.{{sfn|Rudall|2007}}{{sfn|Dickison|2000}}<ref name=SimpsonLv/>
The vein or veins entering the leaf from the petiole are called primary or first-order veins. The veins branching from these are secondary or second-order veins. These primary and secondary veins are considered major veins or lower order veins, though some authors include third order.{{sfn|Sack|Scoffoni|2013}} Each subsequent branching is sequentially numbered, and these are the higher order veins, each branching being associated with a narrower vein diameter.{{sfn|Roth-Nebelsick et al|2001}}
In parallel veined leaves, the primary veins run parallel and equidistant to each other for most of the length of the leaf and then converge or fuse (anastomose) toward the apex. Usually, many smaller minor veins interconnect these primary veins but may terminate with fine vein endings in the mesophyll. Minor veins are more typical of angiosperms, which may have as many as four higher orders.{{sfn|Sack|Scoffoni|2013}}
In contrast, leaves with reticulate venation have a single (sometimes more) primary vein in the center of the leaf, referred to as the midrib or costa, which is continuous with the vasculature of the petiole. The secondary veins, also known as second order veins or lateral veins, branch off from the midrib and extend toward the leaf margins. These often terminate in a [[hydathode]], a secretory organ, at the margin. In turn, smaller veins branch from the secondary veins, known as tertiary or third order (or higher order) veins, forming a dense reticulate pattern. The areas or islands of mesophyll lying between the higher order veins, are called [[wikt:areola|areoles]]. Some of the smallest veins (veinlets) may have their endings in the areoles, a process known as areolation.{{sfn|Roth-Nebelsick et al|2001}} These minor veins act as the sites of exchange between the mesophyll and the plant's vascular system.{{sfn|Walls|2011}} Thus, minor veins collect the products of photosynthesis (photosynthate) from the cells where it takes place, while major veins are responsible for its transport outside of the leaf. At the same time water is being transported in the opposite direction.{{sfn|Ueno et al|2006}}{{sfn|Rudall|2007}}{{sfn|Dickison|2000}}
The number of vein endings is variable, as is whether second order veins end at the margin, or link back to other veins.<ref name=SimpsonLv/> There are many elaborate variations on the patterns that the leaf veins form, and these have functional implications. Of these, angiosperms have the greatest diversity.{{sfn|Sack|Scoffoni|2013}} Within these the major veins function as the support and distribution network for leaves and are correlated with leaf shape. For instance, the parallel venation found in most monocots correlates with their elongated leaf shape and wide leaf base, while reticulate venation is seen in simple entire leaves, while digitate leaves typically have venation in which three or more primary veins diverge radially from a single point.{{sfn|Runions et al|2005}}{{sfn|Walls|2011}}{{sfn|Roth-Nebelsick et al|2001}}<ref name=MMsvt/>
In evolutionary terms, early emerging taxa tend to have dichotomous branching with reticulate systems emerging later. Veins appeared in the [[Permian]], prior to the appearance of angiosperms in the [[Triassic]], during which vein hierarchy appeared enabling higher function, larger leaf size and adaption to a wider variety of climatic conditions.{{sfn|Sack|Scoffoni|2013}} Although it is the more complex pattern, branching veins appear to be [[plesiomorph]]ic and in some form were present in ancient [[seed plant]]s as long as 250 million years ago. A pseudo-reticulate venation that is actually a highly modified penniparallel one is an [[autapomorph]]y of some [[Melanthiaceae]], which are monocots; e.g., ''[[Paris quadrifolia]]'' (true-lover's knot). In leaves with reticulate venation, veins form a scaffolding matrix imparting mechanical rigidity to leaves.{{sfn|Bagchi et al|2016}}
===Morphology changes within a single plant===
;[[Homoblasty]]: Characteristic in which a plant has small changes in leaf size, shape, and growth habit between juvenile and adult stages, in contrast to;
;[[Heteroblasty]]: Characteristic in which a plant has marked changes in leaf size, shape, and growth habit between juvenile and adult stages.
==Anatomy==
===Medium-scale features===
Leaves are normally extensively vascularized and typically have networks of [[vascular bundles]] containing [[xylem]], which supplies water for [[photosynthesis]], and [[phloem]], which transports the [[sugar]]s produced by photosynthesis. Many leaves are covered in [[trichome]]s (small hairs) having diverse structures and functions.
[[File:Leaf Structure.svg|center|600px|Medium-scale diagram of leaf internal anatomy]]
===Small-scale features===
The major tissue systems present are * The '''[[epidermis (botany)|epidermis]]''', which covers the upper and lower surfaces * The '''[[#Mesophyll|mesophyll tissue]]''', which consists of photosynthetic cells rich in [[chloroplast]]s. (also called '''chlorenchyma''') * The arrangement of '''veins''' (the [[vascular tissue]])
These three tissue systems typically form a regular organization at the cellular scale. Specialized cells that differ markedly from surrounding cells, and that often synthesize specialized products such as crystals, are termed '''idioblasts'''.{{sfn|Cote|2009}}
[[File:Leaf Tissue Structure.svg|center|600px|Fine-scale diagram of leaf structure]]
===Major leaf tissues=== <div style="text-align:center;"><gallery> File:Bifacial leaf cross section.jpg|Cross-section of a leaf File:Leaf epidermis 2.jpg|Epidermal cells File:Leaf spongy mesophyll.jpg|Spongy mesophyll cells </gallery></div>
====Epidermis==== [[File:Leaf epidermis w scale.jpg|thumb|[[Scanning electron microscope|SEM]] image of the leaf epidermis of ''[[Nicotiana alata]]'', showing [[trichome]]s (hair-like appendages) and [[stoma]]ta (eye-shaped slits, visible at full resolution)]] The [[epidermis (botany)|epidermis]] is the outer layer of [[cell (biology)|cells]] covering the leaf. It is covered with a waxy [[plant cuticle|cuticle]] that is impermeable to liquid water and water vapor and forms the boundary separating the plant's inner cells from the external world. The cuticle is in some cases thinner on the lower epidermis than on the upper epidermis, and is generally thicker on leaves from dry climates as compared with those from wet climates.{{sfn|Clements|1905}} The epidermis serves several functions: protection against water loss by way of [[transpiration]], regulation of gas exchange and secretion of [[secondary metabolite|metabolic]] compounds. Most leaves show dorsoventral anatomy: The upper (adaxial) and lower (abaxial) surfaces have somewhat different construction and may serve different functions.
The epidermis tissue includes several differentiated cell types; epidermal cells, epidermal hair cells ([[trichome]]s), cells in the stomatal complex; guard cells and subsidiary cells. The epidermal cells are the most numerous, largest, and least specialized and form the majority of the epidermis. They are typically more elongated in the leaves of [[monocot]]s than in those of [[dicot]]s.
Chloroplasts are generally absent in epidermal cells, the exception being the guard cells of the [[stomata]]. The stomatal pores perforate the epidermis and are surrounded on each side by chloroplast-containing guard cells, and two to four subsidiary cells that lack chloroplasts, forming a specialized cell group known as the stomatal complex. The opening and closing of the stomatal aperture is controlled by the stomatal complex and regulates the exchange of gases and water vapor between the outside air and the interior of the leaf. Stomata therefore play the important role in allowing photosynthesis without letting the leaf dry out. In a typical leaf, the stomata are more numerous over the abaxial (lower) epidermis than the adaxial (upper) epidermis and are more numerous in plants from cooler climates.
====Mesophyll==== {{for|the term ''Mesophyll'' in the size classification of leaves|Leaf size}} Most of the interior of the leaf between the upper and lower layers of epidermis is a ''[[parenchyma]]'' (ground tissue) or ''[[chlorenchyma]]'' tissue called the '''mesophyll''' (Greek for "middle leaf"). This [[assimilation (biology)|assimilation]] tissue is the primary location of photosynthesis in the plant. The products of photosynthesis are called "assimilates".
In ferns and most flowering plants, the mesophyll is divided into two layers: * An upper '''[[palisade cell|palisade layer]]''' of vertically elongated cells, one to two cells thick, directly beneath the adaxial epidermis, with intercellular air spaces between them. Its cells contain many more chloroplasts than the spongy layer. Cylindrical cells, with the ''[[chloroplasts]]'' close to the walls of the cell, can take optimal advantage of light. The slight separation of the cells provides maximum [[absorption (chemistry)|absorption]] of carbon dioxide. Sun leaves have a multi-layered palisade layer, while shade leaves or older leaves closer to the soil are single-layered. * Beneath the palisade layer is the '''spongy layer'''. The cells of the spongy layer are more branched and not so tightly packed, so that there are large intercellular air spaces between them. The pores or ''stomata'' of the epidermis open into substomatal chambers, which are connected to the intercellular air spaces between the spongy and palisade mesophyll cell, so that oxygen, carbon dioxide and water vapor can diffuse into and out of the leaf and access the mesophyll cells during respiration, photosynthesis and transpiration.
Leaves are normally green, due to chlorophyll in chloroplasts in the mesophyll cells. Some plants have leaves of different colors due to the presence of [[accessory pigment]]s such as [[carotenoid]]s in their mesophyll cells.
====Vascular tissue==== [[File:BrambleLeaf CrossPolarisedLight Diagram.jpg|thumb|The veins of a [[bramble]] leaf]]
The '''veins''' are the [[vascular tissue]] of the leaf and are located in the spongy layer of the mesophyll. The pattern of the veins is called [[#Venation (arrangement of the veins)|venation]]. In [[angiosperms]] the venation is typically parallel in [[monocotyledons]] and forms an interconnecting network in [[dicotyledon|broad-leaved plants]]. They were once thought to be typical examples of [[pattern formation]] through [[ramification (botany)|ramification]], but they may instead exemplify a pattern formed in a stress [[tensor field]].{{sfn|Couder et al|2002}}{{sfn|Corson et al|2009}}{{sfn|Laguna et al|2008}}
A vein is made up of a [[vascular bundle]]. At the core of each bundle are clusters of two distinct types of conducting cells: ; [[Xylem]]: Cells that bring water and minerals from the roots into the leaf. ; [[Phloem]]: Cells that usually move [[sap]], with dissolved sucrose (glucose to sucrose) produced by photosynthesis in the leaf, out of the leaf.
The xylem typically lies on the adaxial side of the vascular bundle and the phloem typically lies on the abaxial side. Both are embedded in a dense parenchyma tissue, called the sheath, which usually includes some structural collenchyma tissue.
==Leaf development==
According to [[Agnes Arber]]'s partial-shoot theory of the leaf, leaves are partial shoots,{{sfn|Arber|1950}} being derived from leaf [[primordia]] of the shoot apex. Early in development they are dorsiventrally flattened with both dorsal and ventral surfaces.{{sfn|Simpson|2011|loc=p. 356}} Compound leaves are closer to shoots than simple leaves. Developmental studies have shown that compound leaves, like shoots, may branch in three dimensions.{{sfn|Rutishauser|Sattler|1997}}{{sfn|Lacroix et al|2003}} On the basis of molecular genetics, Eckardt and Baum (2010) concluded that "it is now generally accepted that compound leaves express both leaf and shoot properties."{{sfn|Eckardt|Baum|2010}} Many dicotyledonous leaves show endogenously driven daily rhythmicity in growth.<ref>{{Cite journal |last1=Poiré |first1=Richard |last2=Wiese-Klinkenberg |first2=Anika |last3=Parent |first3=Boris |last4=Mielewczik |first4=Michael |last5=Schurr |first5=Ulrich |last6=Tardieu |first6=François |last7=Walter |first7=Achim |date=2010 |title=Diel time-courses of leaf growth in monocot and dicot species: endogenous rhythms and temperature effects |journal=Journal of Experimental Botany |language=en |volume=61 |issue=6 |pages=1751–1759 |doi=10.1093/jxb/erq049 |issn=1460-2431 |pmc=2852670 |pmid=20299442}}</ref><ref>{{Cite journal |last1=Mielewczik |first1=Michael |last2=Friedli |first2=Michael |last3=Kirchgessner |first3=Norbert |last4=Walter |first4=Achim |date=July 25, 2013 |title=Diel leaf growth of soybean: a novel method to analyze two-dimensional leaf expansion in high temporal resolution based on a marker tracking approach (Martrack Leaf) |journal=Plant Methods |language=en |volume=9 |issue=1 |page=30 |doi=10.1186/1746-4811-9-30 |doi-access=free |pmid=23883317 |pmc=3750653 |bibcode=2013PlMet...9...30M |issn=1746-4811 |hdl=20.500.11850/76534 |hdl-access=free}}</ref><ref>{{Cite journal |last1=Friedli |first1=Michael |last2=Walter |first2=Achim |date=2015 |title=Diel growth patterns of young soybean (G lycine max) leaflets are synchronous throughout different positions on a plant |url=https://onlinelibrary.wiley.com/doi/10.1111/pce.12407 |journal=Plant, Cell & Environment |language=en |volume=38 |issue=3 |pages=514–524 |doi=10.1111/pce.12407 |pmid=25041284 |bibcode=2015PCEnv..38..514F |issn=0140-7791}}</ref>
== Ecology ==
=== Biomechanics === Plants respond and adapt to environmental factors, such as light and mechanical stress from wind. Leaves need to support their own mass and align themselves in such a way as to optimize their exposure to the sun, generally more or less horizontally. However, horizontal alignment maximizes exposure to bending forces and failure from stresses such as wind, snow, hail, falling debris, animals, and abrasion from surrounding foliage and plant structures. Overall leaves are relatively flimsy with regard to other plant structures such as stems, branches and roots.{{sfn|Read|Stokes|2006}}
Both leaf blade and petiole structure influence the leaf's response to forces such as wind, allowing a degree of repositioning to minimize [[drag (physics)|drag]] and damage, as opposed to resistance. Leaf movement like this may also increase [[turbulence]] of the air close to the surface of the leaf, which thins the [[boundary layer]] of air immediately adjacent to the surface, increasing the capacity for gas and heat exchange, as well as photosynthesis. Strong wind forces may result in diminished leaf number and surface area, which while reducing drag, involves a [[trade off]] of also reducing photosynthesis. Thus, leaf design may involve compromise between carbon gain, thermoregulation and water loss on the one hand, and the cost of sustaining both static and dynamic loads. In vascular plants, perpendicular forces are spread over a larger area and are relatively flexible in both bending and [[Torsion (mechanics)|torsion]], enabling elastic deforming without damage.{{sfn|Read|Stokes|2006}}
Many leaves rely on [[hydrostatic]] support arranged around a skeleton of vascular tissue for their strength, which depends on maintaining leaf water status. Both the mechanics and architecture of the leaf reflect the need for transportation and support. Read and Stokes (2006) consider two basic models, the "hydrostatic" and "I-beam leaf" form (see Fig 1).{{sfn|Read|Stokes|2006}} Hydrostatic leaves such as in ''[[Prostanthera lasianthos]]'' are large and thin, and may involve the need for multiple leaves rather single large leaves because of the amount of veins needed to support the periphery of large leaves. But large leaf size favors efficiency in photosynthesis and water conservation, involving further trade offs. On the other hand, I-beam leaves such as ''[[Banksia marginata]]'' involve specialized structures to stiffen them. These I-beams are formed from bundle sheath extensions of [[sclerenchyma]] meeting stiffened sub-epidermal layers. This shifts the balance from reliance on hydrostatic pressure to structural support, an obvious advantage where water is relatively scarce. {{sfn|Read|Stokes|2006}} Long narrow leaves bend more easily than ovate leaf blades of the same area. Monocots typically have such linear leaves that maximize surface area while minimizing self-shading. In these a high proportion of longitudinal main veins provide additional support.{{sfn|Read|Stokes|2006}}
=== Interactions with other organisms === [[File:Kallima inachus2.jpg|thumb|Some [[insect]]s, like ''[[Kallima inachus]]'', mimic leaves.]]
Although not as nutritious as other organs such as fruit, leaves provide a food source for many organisms. The leaf is a vital source of energy production for the plant, and plants have evolved protection against animals that consume leaves, such as [[tannin]]s, chemicals that hinder the digestion of proteins and have an unpleasant taste. Animals that are specialized to eat leaves are known as [[folivore]]s.
Some species have [[crypsis|cryptic]] adaptations by which they use leaves in avoiding predators. For example, the caterpillars of [[Tortricidae|some leaf-roller moths]] create a small home in the leaf by folding it over themselves. Several other [[lepidopteran]] larvae modify leaves for shelter; perhaps the greatest variety of shelter types occurs among the [[skipper butterflies]] (Hesperiidae), which cut, fold, and bind leaves using [[silk]].<ref>{{cite journal |last1=Greeney |first1=Harold F |last2=Jones |first2=Meg T |title=Shelter building in the Hesperiidae: a classification scheme for larval shelters |journal=The Journal of Research on the Lepidoptera |volume=37 |date=2003 |doi=10.5962/p.266551 |doi-access=free |pages=27–36 |url=https://www.biodiversitylibrary.org/partpdf/266551 |access-date=January 13, 2025}}</ref> Some [[Pamphiliidae|sawflies]] similarly roll the leaves of their food plants into tubes. Females of the [[Attelabidae]], so-called leaf-rolling weevils, lay their eggs into leaves that they then roll up as means of protection. Other herbivores and their predators [[mimicry|mimic]] the appearance of the leaf. Reptiles such as some chameleons, and insects such as some [[Tettigoniidae|katydids]], also mimic the oscillating movements of leaves in the wind, moving from side to side or back and forth while evading a possible threat.
===Seasonal leaf loss=== [[File:Leaves in autumn.jpg|thumb|Leaves shifting color in autumn (fall)]] {{main|Autumn leaf color}}
Leaves in [[temperate]], [[boreal ecosystem|boreal]], and seasonally dry zones may be seasonally deciduous (falling off or dying for the inclement season). This mechanism to shed leaves is called [[abscission]]. When the leaf is shed, it leaves a leaf scar on the twig. In cold autumns, they sometimes [[autumn leaf color|change color]], and turn [[yellow]], bright-[[orange (colour)|orange]], or [[red]], as various accessory pigments ([[carotenoid]]s and [[xanthophyll]]s) are revealed when the tree responds to cold and reduced [[sunlight]] by curtailing chlorophyll production. Red [[anthocyanin]] pigments are now thought to be produced in the leaf as it dies, possibly to mask the yellow hue left when the chlorophyll is lost—yellow leaves appear to attract herbivores such as [[aphids]].{{sfn|Doring et al|2009}} Optical masking of chlorophyll by anthocyanins reduces risk of photo-oxidative damage to leaf cells as they senesce, which otherwise may lower the efficiency of nutrient retrieval from senescing autumn leaves.{{sfn|Feild et al|2001}}
==Evolutionary adaptation== [[File:Inflorescence 1.jpg|thumb|[[Poinsettia]] [[bract]]s are leaves that have evolved red pigmentation to attract insects and birds to the central flowers, an adaptive function normally served by [[petal]]s (which are themselves leaves highly modified by evolution).]]
In the course of [[evolution]], leaves have adapted to different [[environment (biophysical)|environments]] in the following ways:{{Citation needed|date=April 2019}} * [[Epicuticular wax|Waxy]] micro- and nanostructures on the surface reduce wetting by rain and adhesion of contamination (''See [[Lotus effect]]''). * Divided and compound leaves reduce wind resistance and promote cooling. * Hairs on the leaf surface trap humidity in dry climates and create a [[boundary layer]] reducing water loss. * [[Wax]]y plant cuticles reduce water loss. * Large surface area provides a large area for capture of sunlight. * In harmful levels of sunlight, specialized leaves, opaque or partly buried, admit light through a translucent [[leaf window]] for photosynthesis at inner leaf surfaces (e.g. ''[[Fenestraria]]''). * [[Kranz leaf anatomy]] in plants that perform [[C4 carbon fixation|{{C4}} carbon fixation]] * [[Succulent]] leaves store water and organic acids for use in [[CAM photosynthesis]]. * [[Aromatic oil]]s, [[poisons]] or [[pheromones]] produced by leaf borne glands deter herbivores (e.g. [[eucalypts]]). * Inclusions of crystalline minerals deter herbivores (e.g. silica [[phytolith]]s in grasses, [[raphides]] in [[Araceae]]). * [[Petal]]s attract pollinators. * [[Spine (botany)|Spines]] protect the plants from herbivores (e.g. [[Cactus|cacti]]). * [[Stinging plant|Stinging hairs]] to protect against herbivory, e.g. in ''[[Urtica dioica]]'' and ''[[Dendrocnide moroides]]'' ([[Urticaceae]]). * Special leaves on carnivorous plants are adapted for trapping food, mainly invertebrate prey, though some species trap small vertebrates as well (see [[carnivorous plant]]s). * [[Bulb]]s store food and water (e.g. [[onion]]s). * [[Tendril]]s allow the plant to climb (e.g. peas). * [[Bract]]s and [[pseudanthium|pseudanthia]] (false flowers) replace normal flower structures when the true flowers are greatly reduced (e.g. [[spurge]]s, [[spathe]]s in the [[Araceae]] and [[Pseudanthium|floral heads]] in the [[Asteraceae]]).
==Terminology== {{see also|Glossary of leaf morphology|Glossary of plant morphology|Glossary of botanical terms}} [[File:Leaf morphology.svg|thumb|left|upright=3|Leaf morphology terms]] {{Clear}}
===Shape=== {{main|Glossary of leaf morphology#Leaf and leaflet shapes}} [[File:Leaves-scan.jpg|thumb|upright=1.2|left|Leaves showing various morphologies (clockwise from upper left): tripartite lobation, elliptic with serrulate margin, palmate venation, acuminate odd-pinnate (center), pinnatisect, lobed, elliptic with entire margin]] {{Clear}} {{anchor|Margins (edge)}} ===Edge (margin)=== The ''edge'' or ''margin'' is the outside perimeter of a leaf. The terms are interchangeable. {{Leaf margin}}
{{anchor|Tip of the leaf}} ===Apex (tip)<span class="anchor" id="Apex (tip)"></span>=== {| class="wikitable sortable center" |- ! scope="col" class="unsortable"| Image ! scope="col"| Term ! scope="col"| Latin ! scope="col"| Description |- |[[File:Handdrawn Acuminate.png|64px]]||Acuminate||''_''||Long-pointed, prolonged into a narrow, tapering point in a concave manner |- |[[File:Handdrawn Acute.png|64px]]||Acute||''_''||Ending in a sharp, but not prolonged point |- |[[File:Handdrawn Cuspidate.png|64px]]||Cuspidate||''_''||With a sharp, elongated, rigid tip; tipped with a cusp |- |[[File:Handdrawn Emarginate.png|64px]]||Emarginate||''_''||Indented, with a shallow notch at the tip |- |[[File:Handdrawn Mucronate.png|64px]]||Mucronate||''_''||Abruptly tipped with a small short point |- |[[File:Handdrawn Mucronate.png|64px]]||Mucronulate||''_''||Mucronate, but with a noticeably diminutive spine |- |[[File:Handdrawn Obcordate.png|64px]]||Obcordate||''_''||Inversely heart-shaped |- |[[File:Handdrawn Obtuse.png|64px]]||Obtuse||''_''||Rounded or blunt |- |[[File:Handdrawn Truncate.png|64px]]||Truncate||''_''||Ending abruptly with a flat end |}
{{anchor|Base of the leaf}} ===Base=== ;Acuminate: Coming to a sharp, narrow, prolonged point. ;Acute: Coming to a sharp, but not prolonged point. ;Auriculate: Ear-shaped. ;Cordate: Heart-shaped with the notch toward the stalk. ;Cuneate: Wedge-shaped. ;Hastate: Shaped like an halberd and with the basal lobes pointing outward. ;Oblique: Slanting. ;Reniform: Kidney-shaped but rounder and broader than long. ;Rounded: Curving shape. ;Sagittate: Shaped like an arrowhead and with the acute basal lobes pointing downward. ;Truncate: Ending abruptly with a flat end, that looks cut off.
{{anchor|Surface of the leaf}} ===Surface=== [[File:Araucaria columnaris leaves, Kauai, Hawaii 1758c.jpg|thumb|The scale-shaped leaves of the [[Araucaria heterophylla|Norfolk Island pine]]]]
The leaf surface is also host to a large variety of [[microorganisms]]; in this context it is referred to as the [[phyllosphere]]. ;Lepidote: Covered with fine scurfy scales.
{{anchor|Hairiness (trichomes)}} ===Hairiness=== [[File:Starr 040723-0032 Verbascum thapsus.jpg|thumb|Common mullein (''[[Verbascum thapsus]]'') leaves are covered in dense, stellate trichomes.]] [[File:Coleus leaf trichomes SEM.jpg|thumb|Scanning electron microscope image of trichomes on the lower surface of a ''Coleus blumei'' ([[coleus]]) leaf]] [[File:Symphyotrichum sericeum 10135056.jpg|thumb|Silky aster (''[[Symphyotrichum sericeum]]'') leaves are sericeous.]] "Hairs" on plants are properly called [[trichome]]s. Leaves can show several degrees of hairiness. The meaning of several of the following terms can overlap. ;Arachnoid, or arachnose: With many fine, entangled hairs giving a cobwebby appearance. ;Barbellate: With finely barbed hairs (barbellae). ;Bearded: With long, stiff hairs. ;Bristly: With stiff hair-like prickles. ;Canescent: Hoary with dense grayish-white [[pubescence (botany)|pubescence]]. ;Ciliate: Marginally fringed with short hairs (cilia). ;Ciliolate: Minutely ciliate. ;Floccose: With flocks of soft, woolly hairs, which tend to rub off. ;Glabrescent: Losing hairs with age. ;Glabrous: No hairs of any kind present. ;Glandular: With a gland at the tip of the hair. ;Hirsute: With rather rough or stiff hairs. ;Hispid: With rigid, bristly hairs. ;Hispidulous: Minutely hispid. ;Hoary: With a fine, close grayish-white pubescence. ;{{anchor|lanate|lanose}}Lanate, or lanose: With woolly hairs. ;Pilose: With soft, clearly separated hairs. ;Puberulent, or puberulous: With fine, minute hairs. ;{{anchor|pubescent}}Pubescent: With soft, short and erect hairs. ;Scabrous, or scabrid: Rough to the touch. ;Sericeous: Silky appearance through fine, straight and appressed (lying close and flat) hairs. ;Silky: With adpressed, soft and straight pubescence. ;Stellate, or stelliform: With star-shaped hairs. ;Strigose: With appressed, sharp, straight and stiff hairs. ;Tomentose: Densely pubescent with matted, soft white woolly hairs.{{glossary}}{{term|Cano-tomentose}}{{defn|Between canescent and tomentose.}}{{term|Felted-tomentose}}{{defn|Woolly and matted with curly hairs.}}{{glossary end}} ;Tomentulose: Minutely or only slightly tomentose. ;{{anchor|villous}}Villous: With long and soft hairs, usually curved. ;Woolly: With long, soft and tortuous or matted hairs.
===Timing=== ;Hysteranthous: Developing after the flowers <ref>{{Cite web |url=http://www.kew.org/Glossary/hysteranthous.htm?prefix=h |title=Kew Glossary – definition of hysteranthous |date=December 3, 2013 |access-date=May 12, 2017 |archive-date=December 3, 2013 |archive-url=https://web.archive.org/web/20131203015400/http://www.kew.org/Glossary/hysteranthous.htm?prefix=h |url-status=bot: unknown}}</ref> ;Synanthous: Developing at the same time as the flowers <ref>{{Cite web |url=http://www.kew.org/Glossary/synanthous.htm?prefix=s |title=Kew Glossary – definition of synanthous |date=December 3, 2013 |access-date=May 12, 2017 |archive-date=December 3, 2013 |archive-url=https://web.archive.org/web/20131203015354/http://www.kew.org/Glossary/synanthous.htm?prefix=s |url-status=bot: unknown}}</ref>
=== Venation ===
==== Classification ==== {{multiple image | header = Hickey primary venation types | align = right | direction = vertical | width = 200 | float = none | image1 = Ostrya virginiana1.jpg | caption1 = 1. Pinnate venation, ''[[Ostrya virginiana]]'' | alt1 = | image2 = Tulip Leaves AWL.JPG|thumb | caption2 = 2. Parallel venation, ''[[Iris (plant)|Iris]]'' | image3 = Maianthemum bifolium 2.JPG | caption3 = 3. Campylodromous venation, ''[[Maianthemum bifolium]]'' | image4 = Starr 031118-0115 Miconia calvescens.jpg | caption4 = 4. Acrodromous venation (basal), ''[[Miconia calvescens]]'' | image5 = Puttali (Tamil- பூத்தாளி) (5656476463).jpg | caption5 = 5. Actinodromous venation (suprabasal), ''[[Givotia moluccana]]'' | image6 = Platanus orientalis leaf.JPG | caption6 = 6. Palinactodromous venation, ''[[Platanus orientalis]]'' }} A number of different classification systems of the patterns of leaf veins (venation or veination) have been described,<ref name=SimpsonLv/> starting with Ettingshausen (1861),{{sfn|Ettingshausen|1861}} together with many different descriptive terms, and the terminology has been described as "formidable".<ref name=SimpsonLv/> One of the commonest among these is the Hickey system, originally developed for "[[dicotyledons]]" and using a number of Ettingshausen's terms derived from Greek (1973–1979):{{sfn|Hickey|1973}}{{sfn|Hickey|Wolfe|1975}}{{sfn|Hickey|1979}} (''see also'': Simpson Figure 9.12, p. 468)<ref name=SimpsonLv/>
===== Hickey system ===== ;1. [[Pinnate]] (feather-veined, reticulate, pinnate-netted, penniribbed, penninerved, or penniveined): The veins arise [[pinnately]] (feather like) from a single primary vein (mid-vein) and subdivide into secondary veinlets, known as higher order veins. These, in turn, form a complicated network. This type of venation is typical for (but by no means limited to) "[[dicotyledon]]s" (non monocotyledon [[angiosperms]]). E.g., ''[[Ostrya]]''.{{paragraph}} There are three subtypes of pinnate venation:{{glossary}}{{term | ''Craspedodromous''}}{{defn | The major veins reach to the margin of the leaf.}}{{term | ''Camptodromous''}}{{defn | Major veins extend close to the margin, but bend before they intersect with the margin.}}{{term | ''Hyphodromous''}}{{defn | All secondary veins are absent, rudimentary or concealed}}{{glossary end}} These in turn have a number of further subtypes such as eucamptodromous, where secondary veins curve near the margin without joining adjacent secondary veins. {{multiple image | header = Pinnate | align = center | direction = horizontal | width = 140 | float = none | image1 = Leaf morphology - venation Hickey 1973 - craspedodromous simple.svg | caption1 = Craspedodromous | image2 = Leaf morphology - venation Hickey 1973 - camptodromous eucamptodromous.svg | caption2 = Camptodromous | image3 = Leaf morphology - venation Hickey 1973 - hyphodromous.svg | caption3 = Hyphodromous }}
;2. Parallelodromous (parallel-veined, parallel-ribbed, parallel-nerved, penniparallel, striate): Two or more primary veins originating beside each other at the leaf base, and running [[Parallel (geometry)|parallel]] to each other to the apex and then converging there. Commissural veins (small veins) connect the major parallel veins. Typical for most [[monocotyledon]]s, such as [[Poaceae|grasses]].{{paragraph}} The additional terms marginal (primary veins reach the margin), and reticulate (net-veined) are also used. {{multiple image | header = Parallelodromous | align = center | direction = horizontal | float = none | image1 = Leaf morphology - venation Hickey 1973 - parallelodromous.svg }}
;3. Campylodromous (''{{lang|grc-Latn|campylos}}'' – curve): Several primary veins or branches originating at or close to a single point and running in recurved arches, then converging at apex. E.g. ''[[Maianthemum]]'' . {{multiple image | header = Campylodromous | align = center | direction = horizontal | float = none | image1 =Leaf morphology - venation Hickey 1973 - campylodromous.svg }}
;4. Acrodromous: Two or more primary or well developed secondary veins in convergent arches toward apex, without basal recurvature as in Campylodromous. May be basal or suprabasal depending on origin, and perfect or imperfect depending on whether they reach to two-thirds of the way to the apex. E.g., ''[[Miconia]]'' (basal type), ''[[Endlicheria]]'' (suprabasal type). {{multiple image | header = Acrodromous | align = center | direction = horizontal | width = 75 | float = none | image1 = Leaf morphology - venation Hickey 1973 - acrodromous imperfect basal.svg | caption1 = Imperfect basal | image2 = Leaf morphology - venation Hickey 1973 - acrodromous imperfect suprabasal.svg | caption2=Imperfect suprabasal | image3=Leaf morphology - venation Hickey 1973 - acrodromous perfect basal.svg | caption3=Perfect basal | image4=Leaf morphology - venation Hickey 1973 - acrodromous perfect suprabasal.svg | caption4=Perfect suprabasal }}
;5. Actinodromous: Three or more primary veins diverging radially from a single point. E.g., ''[[Arcangelisia]]'' (basal type), ''[[Givotia]]'' (suprabasal type). {{multiple image | header = Actinodromous | align = center | direction = horizontal | width = 75 | float = none | image1 = Leaf morphology - venation Hickey 1973 - actinodromous imperfect marginal.svg | caption1 = Imperfect marginal | image2 = Leaf morphology - venation Hickey 1973 - actinodromous imperfect reticulate.svg | caption2 = Imperfect reticulate {{Dubious|date=April 2022}} }}
;6. Palinactodromous: Primary veins with one or more points of secondary dichotomous branching beyond the primary divergence, either closely or more distantly spaced. E.g., ''[[Platanus]]''.
[[File:PoinsettiaVenation.jpg|alt=Venation of a poinsettia (Euphorbia pulcherrima) leaf|thumb|Venation of a poinsettia (''[[Euphorbia pulcherrima]]'') leaf]] {{multiple image | header = Palinactodromous | align = center | direction = horizontal | float = none | image1 =Leaf morphology - venation Hickey 1973 - palinactinodromous.svg }}
Types 4–6 may similarly be subclassified as basal (primaries joined at the base of the blade) or suprabasal (diverging above the blade base), and perfect or imperfect, but also flabellate.
At about the same time, Melville (1976) described a system applicable to all Angiosperms and using Latin and English terminology.{{sfn|Melville|1976}} Melville also had six divisions, based on the order in which veins develop.
; Arbuscular (arbuscularis): Branching repeatedly by regular dichotomy to give rise to a three dimensional bush-like structure consisting of linear segment (2 subclasses) ; Flabellate (flabellatus): Primary veins straight or only slightly curved, diverging from the base in a fan-like manner (4 subclasses) ; Palmate (palmatus): Curved primary veins (3 subclasses) ; Pinnate (pinnatus): Single primary vein, the midrib, along which straight or arching secondary veins are arranged at more or less regular intervals (6 subclasses) ; Collimate (collimatus): Numerous longitudinally parallel primary veins arising from a transverse meristem (5 subclasses) ; Conglutinate (conglutinatus): Derived from fused pinnate leaflets (3 subclasses)
A modified form of the Hickey system was later incorporated into the Smithsonian classification (1999), which proposed seven main types of venation, based on the architecture of the primary veins, adding Flabellate as an additional main type. Further classification was then made on the basis of secondary veins, with 12 further types, such as; ; Brochidodromous: Closed form in which the secondaries are joined in a series of prominent arches, as in ''[[Hildegardia (plant)|Hildegardia]]''. ; Craspedodromous: Open form with secondaries terminating at the margin, in toothed leaves, as in ''[[Celtis]]''. ; Eucamptodromous: Intermediate form with upturned secondaries that gradually diminish apically but inside the margin, and connected by intermediate tertiary veins rather than loops between secondaries, as in ''[[Cornus]]''. ; Cladodromous: Secondaries freely branching toward the margin, as in ''[[Rhus]]''.
terms that had been used as subtypes in the original Hickey system.{{sfn|Leaf Architecture Working Group|1999}} {{multiple image | header = Secondary venation patterns | align = center | direction = horizontal | float = none | image1 = Leaf morphology - venation Hickey 1973 - camptodromous brochidodromous.svg | caption1 = Brochidodromous | image2=Leaf morphology - venation Hickey 1973 - craspedodromous simple.svg | caption2 = Craspedodromous | image3=Leaf morphology - venation Hickey 1973 - camptodromous eucamptodromous.svg | caption3=Eucamptodromous | image4=Leaf morphology - venation Hickey 1973 - camptodromous cladodromous.svg | caption4=Cladodromous }} {{multiple image | align = center | image_gap = 10 | image1 =Hildegardia migeodii - leaf shape (8307117710).jpg | caption1 = Brochidodromous<br />''[[Hildegardia (plant)|Hildegardia migeodii]]'' | width1={{#expr: (150 * 1900 /1425) round 0}} | image2=Celtis occidentalis (18).JPG | caption2=Craspedodromous<br />''[[Celtis occidentalis]]'' | width2={{#expr: (150 * 2736 /3192) round 0}} | image3=Cornus officinalis 02.JPG | caption3=Eucamptodromous<br />''[[Cornus officinalis]]'' | width3={{#expr: (150 * 2448/3264) round 0}} | image4=Rhus ovata 1.jpg | caption4=Cladodromous<br />''[[Rhus ovata]]'' | width4={{#expr: (150 * 1500 /1155) round 0}} }}
Further descriptions included the higher order, or minor veins and the patterns of areoles (''see'' Leaf Architecture Working Group, Figures 28–29).{{sfn|Leaf Architecture Working Group|1999}}
[[File:Adiantum cunninghamii.jpg|thumb|Flabellate venation, ''[[Adiantum cunninghamii]]'']] ;Flabellate: Several to many equal fine basal veins diverging radially at low angles and branching apically. E.g. ''[[Paranomus]]''.
{{multiple image | header = Flabellate | align = center | direction = horizontal | width = 75 | float = none | image1 =Leaf morphology - venation Hickey 1973 - flabellate.svg }}
Analyses of vein patterns often fall into consideration of the vein orders, primary vein type, secondary vein type (major veins), and minor vein density. A number of authors have adopted simplified versions of these schemes.{{sfn|Judd et al| 2007}}<ref name=SimpsonLv/> At its simplest the primary vein types can be considered in three or four groups depending on the plant divisions being considered; * pinnate * palmate * parallel
where palmate refers to multiple primary veins that radiate from the petiole, as opposed to branching from the central main vein in the pinnate form, and encompasses both of Hickey types 4 and 5, which are preserved as subtypes; e.g., palmate-acrodromous (''see'' National Park Service Leaf Guide).{{sfn|Florissant Leaf Key|2016}}
[[File:Acer Truncatum leaf.jpg|thumb|Palmate venation, ''[[Acer truncatum]]'' ]] ;Palmate, Palmate-netted, palmate-veined, fan-veined: Several main veins of approximately equal size [[divergence|diverge]] from a common point near the leaf base where the petiole attaches, and radiate toward the edge of the leaf. Palmately veined leaves are often lobed or divided with lobes radiating from the common point. They may vary in the number of primary veins (3 or more), but always radiate from a common point.<ref name=KlingLv/> e.g. most [[maple|''Acer'']] (maples). {{multiple image | header = Palmate | align = center | direction = horizontal | float = none | image1 = Leaf morphology venation palmate.png }}
===== Other systems ===== Alternatively, Simpson uses:<ref name=SimpsonLv/>
; Uninervous: Central midrib with no lateral veins ([[microphyllous]]), seen in the non-seed bearing [[tracheophytes]], such as [[horsetails]] ; [[File:Dichotomous venation of the Gingo biloba.tif|thumb|253x253px|Dichotomous venation of the dorsal side of the Ginkgo biloba leaf.]]Dichotomous: Veins successively branching into equally sized veins from a common point, forming a Y junction, fanning out. Among temperate woody plants, ''[[Ginkgo biloba]]'' is the only species exhibiting dichotomous venation. Also some [[fern|pteridophytes]] (ferns).<ref name=KlingLv/> ; Parallel: Primary and secondary veins roughly parallel to each other, running the length of the leaf, often connected by short perpendicular links, rather than form networks. In some species, the parallel veins join at the base and apex, such as needle-type evergreens and grasses. Characteristic of monocotyledons, but exceptions include ''[[Arisaema]]'', and as below, under netted.<ref name=KlingLv/> ; Netted (reticulate, pinnate): A prominent midvein with secondary veins branching off along both sides of it. The name derives from the ultimate veinlets, which form an interconnecting net like pattern or network. (The primary and secondary venation may be referred to as pinnate, while the net like finer veins are referred to as netted or reticulate); most non-monocot angiosperms, exceptions including ''[[Calophyllum]]''. Some monocots have reticulate venation, including ''[[Colocasia]]'', ''[[Dioscorea]]'' and ''[[Smilax]]''.<ref name=KlingLv/>
However, these simplified systems allow for further division into multiple subtypes. Simpson,<ref name=SimpsonLv/> (and others){{sfn|Berg|2007}} divides parallel and netted (and some use only these two terms for Angiosperms)<ref name=AMVen/> on the basis of the number of primary veins (costa) as follows; ; Parallel:{{glossary}}{{term | Penni-parallel (pinnate, pinnate parallel, unicostate parallel)}}{{defn | Single central prominent midrib, secondary veins from this arise perpendicularly to it and run parallel to each other toward the margin or tip, but do not join (anastomose). The term unicostate refers to the prominence of the single midrib (costa) running the length of the leaf from base to apex. e.g. [[Zingiberales]], such as [[Musa (genus)|Bananas]] etc.}}{{term | Palmate-parallel (multicostate parallel)}}{{defn | Several equally prominent primary veins arising from a single point at the base and running parallel toward tip or margin. The term multicostate refers to having more than one prominent main vein. e.g. [[fan palm|"fan" (palmate) palms]] (Arecaceae){{glossary}}{{term | Multicostate parallel convergent}}{{defn | Mid-veins converge at apex e.g. ''[[Bambusa arundinacea]]'' {{=}} ''B. bambos'' (Aracaceae), ''[[Eichornia]]''}}{{term | Multicostate parallel divergent}}{{defn | Mid-veins diverge more or less parallel toward the margin e.g. ''[[Borassus]]'' (Poaceae), fan palms}}{{glossary end}}}}{{glossary end}} ; Netted (Reticulate):{{glossary }}{{term | Pinnately (veined, netted, unicostate reticulate)}}{{defn | Single prominent midrib running from base to apex, secondary veins arising on both sides along the length of the primary midrib, running toward the margin or apex (tip), with a network of smaller veinlets forming a reticulum (mesh or network). e.g. ''[[Mangifera]]'', ''[[Ficus religiosa]]'', ''[[Psidium guajava]]'', ''[[Hibiscus rosa-sinensis]]'', ''[[Salix alba]]''}}{{term | Palmately (multicostate reticulate)}}{{defn | More than one primary veins arising from a single point, running from base to apex. e.g. ''[[Liquidambar styraciflua]]'' This may be further subdivided;{{glossary}}{{term | Multicostate convergent}}{{defn | Major veins diverge from origin at base then converge toward the tip. e.g. ''[[Zizyphus]]'', ''Smilax'', ''[[Cinnamomum]]''}}{{term | Multicostate divergent}}{{defn | All major veins diverge toward the tip. e.g. ''[[Gossypium]]'', ''[[Cucurbita]]'', ''[[Carica papaya]]'', ''[[Ricinus communis]]''}}{{glossary end}}}}{{term | Ternately (ternate-netted)}}{{defn | Three primary veins, as above, e.g. (''see'') ''[[Ceanothus leucodermis]]'',<ref name=SimpsonCl/> ''[[Ceanothus tomentosus|C. tomentosus]]'',<ref name=SimpsonCt/> ''[[Encelia farinosa]]''}}{{glossary end}} {{multiple image| header = Simpson venation patterns| align = center| direction =| total_width= 800| float = |perrow=4 | image1 = Maranta leuconeura var. erythroneura1.jpg | caption1 = ''[[Maranta leuconeura]]'' var. ''erythroneura'' ([[Zingiberales]]):<br />Penni-parallel | width1={{#expr: (150 * 800 /600) round 0}} | image2= Coccothrinax argentea kz2.JPG | caption2= ''[[Coccothrinax argentea]]'' (Arecaceae):<br />Palmate-parallel | width2={{#expr: (150 * 800 /577) round 0}} | image5 = Salix alba leaf.jpg | caption5 = ''[[Salix alba]]'':<br />Pinnately netted | width5={{#expr: (150 * 138/598) round 0}} | image6= Liquidambar feuilles FR 2013.jpg | caption6= ''[[Liquidambar styraciflua]]'':<br />Palmately netted | width6={{#expr: (150 * 800/549) round 0}} | image3=Plantarum indigenarum et exoticarum icones ad vivum coloratae, oder, Sammlung nach der Natur gemalter Abbildungen inn- und ausländlischer Pflanzen, für Liebhaber und Beflissene der Botanik (15902604278).jpg | caption3=''[[Bambusa bambos]]'':<br />Multicostate parallel convergent | width3={{#expr: (150 * 361/598) round 0}} | image4=SrahSrangTree.jpg | caption4= ''[[Borassus]]'' sp.:<br />Multicostate parallel divergent | width4={{#expr: (150 * 450/600) round 0}} | image7=(Ziziphus jujuba) Foliage at Ammuguda 01.jpg | caption7= ''[[Ziziphus jujuba]]'':<br />Multicostate palmate convergent | width7={{#expr: (150 * 664/600) round 0}} | image8=Starr 050128-3307 Gossypium tomentosum.jpg | caption8= ''[[Gossypium tomentosum]]'':<br />Multicostate palmate divergent | width8={{#expr: (150 * 179/240) round 0}} }}
These complex systems are not used much in morphological descriptions of taxa, but have usefulness in plant identification, <ref name=SimpsonLv/> although criticized as being unduly burdened with jargon.<ref name=HLlv/>
An older, even simpler system, used in some flora{{sfn|Cullen et al|2011}} uses only two categories, open and closed.
* Open: Higher order veins have free endings among the cells and are more characteristic of non-monocotyledon angiosperms. They are more likely to be associated with leaf shapes that are toothed, lobed or compound. They may be subdivided as; ** Pinnate (feather-veined) leaves, with a main central vein or rib (midrib), from which the remainder of the vein system arises ** Palmate, in which three or more main ribs rise together at the base of the leaf, and diverge upward. ** Dichotomous, as in ferns, where the veins fork repeatedly * Closed: Higher order veins are connected in loops without ending freely among the cells. These tend to be in leaves with smooth outlines, and are characteristic of monocotyledons. ** They may be subdivided into whether the veins run parallel, as in grasses, or have other patterns.
==== Other descriptive terms ====
There are also many other descriptive terms, often with specialized usage and confined to specific taxonomic groups.{{sfn|Neotropikey|2017}} The conspicuousness of veins depends on a number of features. These include the width of the veins, their prominence in relation to the lamina surface and the degree of opacity of the surface, which may hide finer veins. In this regard, veins are called '''obscure''' and the order of veins that are obscured and whether upper, lower or both surfaces, further specified.{{sfn|Oxford herbaria glossary|2017}}<ref name=KlingLv/>
Terms that describe vein prominence include '''bullate''', '''channelled''', '''flat''', '''guttered''', '''impressed''', '''prominent''' and '''recessed''' (''Fig''. 6.1 Hawthorne & Lawrence 2013).<ref name=HLlv/><ref name=OxHerbVp/> Veins may show different types of prominence in different areas of the leaf. For instance ''[[Pimenta racemosa]]'' has a channeled midrib on the upper surface, but this is prominent on the lower surface.<ref name=HLlv/>
Describing vein prominence:
;Bullate: Surface of leaf raised in a series of domes between the veins on the upper surface, and therefore also with marked depressions. e.g. ''[[Rytigynia pauciflora]]'',{{sfn|Verdcourt|Bridson|1991}} ''[[Vitis vinifera]]'' ;Channelled (canalicululate): Veins sunken below the surface, resulting in a rounded channel. Sometimes confused with "guttered" because the channels may function as gutters for rain to run off and allow drying, as in many [[Melastomataceae]].<ref name=Hemsley254/> e.g. (''see'') ''[[Pimenta racemosa]]'' (Myrtaceae),<ref name=OxHerbPimrac/> ''[[Clidemia hirta]]'' (Melastomataceae). ;Guttered: Veins partly prominent, the crest above the leaf lamina surface, but with channels running along each side, like gutters ;Impressed: Vein forming raised line or ridge lying below the plane of the surface that bears it, as if pressed into it, and are often exposed on the lower surface. Tissue near the veins often appears to pucker, giving them a sunken or embossed appearance ;Obscure: Veins not visible, or not at all clear; if unspecified, then not visible with the naked eye. e.g. ''[[Berberis gagnepainii]]''. In this ''Berberis'', the veins are only obscure on the undersurface.<ref name=CullenBgag/> ;Prominent: Vein raised above surrounding surface so to be easily felt when stroked with finger. e.g. (''see'') ''[[Pimenta racemosa]]'',<ref name=OxHerbPimrac/> ''[[Spathiphyllum cannifolium]]''<ref name=KwantlenSpcan/> ;Recessed: Vein is sunk below the surface, more prominent than surrounding tissues but more sunken in channel than with impressed veins. e.g. ''[[Viburnum plicatum]]''.
{{multiple image| header = Types of vein prominence| align = center| direction =| total_width= 700| float = |perrow=3 | image1 = Blattadern-wein-P7089798-PS.jpg | caption1 = ''[[Vitis vinifera]]''<br /> Bullate | width1={{#expr: (150 * 800 /600) round 0}} | image2= Flickr - João de Deus Medeiros - Clidemia hirta.jpg | caption2= ''[[Clidemia hirta]]''<br /> Channeled | width2={{#expr: (150 * 800 /600) round 0}} | image3=Cornus mas (3).jpg | caption3=''[[Cornus mas]]''<br />Impressed | width3={{#expr: (150 * 800/435) round 0}} | image4=Berberis gagnepainii thorn.jpg | caption4= ''[[Berberis gagnepainii]]''<br /> Obscure (under surface) | width4={{#expr: (150 * 495/393) round 0}} | image5= Spathiphyllum cannifolium kz2.jpg | caption5 = ''[[Spathiphyllum cannifolium]]''<br /> Prominent | width5={{#expr: (150 * 415/600) round 0}} | image6= Viburnum plicatum var plicatum4.jpg | caption6= ''[[Viburnum plicatum]]''<br /> Recessed | width6={{#expr: (150 * 445/599) round 0}} }}
Describing other features: ;[[wikt:-plinerved|Plinervy]] (plinerved): More than one main vein (nerve) at the base. Lateral secondary veins branching from a point above the base of the leaf. Usually expressed as a [[suffix]], as in 3-plinerved or triplinerved leaf. In a 3-plinerved (triplinerved) leaf three main veins branch above the base of the lamina (two secondary veins and the main vein) and run essentially parallel subsequently, as in ''[[Ceanothus]]'' and in ''[[Celtis occidentalis|Celtis]]''. Similarly, a quintuplinerve (five-veined) leaf has four secondary veins and a main vein. A pattern with 3–7 veins is especially conspicuous in [[Melastomataceae]]. The term has also been used in [[Vaccinieae]]. The term has been used as synonymous with acrodromous, palmate-acrodromous or suprabasal acrodromous, and is thought to be too broadly defined.{{sfn|Pedraza-Peñalosa|2013}}{{sfn|Pedraza-Peñalosa|2013}} ;Scalariform: Veins arranged like the rungs of a ladder, particularly higher order veins ;Submarginal: Veins running close to leaf margin ;Trinerved: 2 major basal nerves besides the midrib
==== Diagrams of venation patterns ==== {| class="wikitable sortable center" ! class="unsortable" | Image ! Term ! class="unsortable" | Description |- |[[file:Leaf morphology arcuate.png|64px]]||Arcuate||Secondary arching toward the apex |- |[[file:Leaf morphology dichotomous.png|64px]]||Dichotomous||Veins splitting in two |- |[[file:Leaf morphology longitudinal.png|64px]]||Longitudinal||All veins aligned mostly with the midvein |- |[[file:Leaf morphology parallel.png|64px]]||Parallel||All veins parallel and not intersecting |- |[[file:Leaf morphology pinnate.png|64px]]||Pinnate||Secondary veins borne from midrib |- id="Reticulate" |[[file:Leaf morphology reticulate.png|64px]]||Reticulate||All veins branching repeatedly, net veined |- |[[file:Leaf morphology rotate.png|64px]]||Rotate||Veins coming from the center of the leaf and radiating toward the edges |- |[[file:Leaf morphology cross venulate.png|64px]]||Transverse||Tertiary veins running perpendicular to axis of main vein, connecting secondary veins |}
===Size=== {{main|Leaf size}} The terms '''megaphyll''', '''macrophyll''', '''mesophyll''', '''notophyll''', '''microphyll''', '''nanophyll''' and '''leptophyll''' are used to describe leaf sizes (in descending order), in a classification devised in 1934 by [[Christen C. Raunkiær]] and since modified by others.{{sfn|Whitten et al|1997}}<ref>{{cite journal |title=A Physiognomic Classification of Australian Rain Forests |first1=Len |last1=Webb |author-link=Leonard Webb (academic) |journal=Journal of Ecology |publisher=British Ecological Society : Journal of Ecology Vol. 47, No. 3, pp. 551–570 |date=October 1, 1959 |volume=47 |issue=3 |page=555 |doi=10.2307/2257290 |jstor=2257290 |bibcode=1959JEcol..47..551W}}</ref>
==See also== {{div col|colwidth=30em}} * [[Glossary of leaf morphology]] * [[Glossary of plant morphology#Leaves|Glossary of plant morphology § Leaves]] * [[Crown (botany)]] * [[Evolution of leaves|Evolutionary history of leaves]] * [[Plant evolutionary developmental biology#Evolution of leaves|Evolutionary development of leaves]] * [[Leaf area index]] * [[Leaf protein concentrate]] * [[Leaf sensor]] – a device that measures the moisture level in plant leaves * [[Leaf shape]] * [[Vernation]] – sprouting of leaves, also the arrangement of leaves in the bud * [[Musical leaf]] {{div col end}}
==References== {{reflist|20em|refs=
<ref name=CullenBgag>{{harvnb|Cullen et al|2011|loc=[https://books.google.com/books?id=zKOyo9qv2HsC&pg=PA398 ''Berberis gagnepainii'' vol. II p. 398] }}</ref>
<ref name=HLlv>{{harvnb|Hawthorne|Lawrence|2013|loc=[https://books.google.com/books?id=CNFuyOVTSf4C&pg=PA135 Leaf venation pp. 135–136] }}</ref>
<ref name=Hemsley254>{{harvnb|Hemsley|Poole|2004|loc=[https://books.google.com/books?id=7Eub0D4QWXIC&pg=PA254 Leaf morphology and drying p. 254] }}</ref>
<ref name=KlingLv>{{harvnb|Kling et al|2005|loc=[http://woodyplantstutorial.nres.illinois.edu/venation/ Leaf Venation] }}</ref>
<ref name=KwantlenSpcan>{{harvnb|Kwantlen|2015|loc=[https://plantdatabase.kpu.ca/plant/plantDetail/1640 ''Spathiphyllum cannifolium''] }}</ref>
<ref name=OxHerbVp>{{harvnb|Oxford herbaria glossary|2017|loc=[http://herbaria-old.plants.ox.ac.uk/vfh/image/?glossary=show&alpha=V#vein_prominence Vein prominence] }}</ref>
<ref name=OxHerbPimrac>{{harvnb|Hughes|2017|loc=[http://herbaria-old.plants.ox.ac.uk/vfh/image/index.php?item=1327&character_image=7164 ''Pimenta racemosa''] }}</ref>
<ref name=MMsvt>{{harvnb|Massey|Murphy|1996|loc=[https://www.ibiblio.org/botnet/glossary/b_iv.html Surface-Venation-Texure] }}</ref>
<ref name=SimpsonLv>{{harvnb|Simpson|2011|loc=[https://books.google.com/books?id=dj8KRImgyf4C&pg=PA465 Leaf venation pp. 465–468] }}</ref>
<ref name=SimpsonCl>{{harvnb|Simpson|2017|loc=[http://www.sci.sdsu.edu/plants/sdpls/plants/Ceanothus_leucodermis.html ''Ceanothus leucodermis''] }}</ref>
<ref name=SimpsonCt>{{harvnb|Simpson|2017|loc=[http://www.sci.sdsu.edu/plants/sdpls/plants/Ceanothus_tomentosus.html ''Ceanothus tomentosus''] }}</ref>
<ref name=AMVen>{{harvnb|Angiosperm Morphology|2017|loc=[http://www.tutorvista.com/content/biology/biology-iii/angiosperm-morphology/venation.php Venation] }}</ref>
}}
== Bibliography == {{refbegin|30em}}
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=== Articles and theses ===
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=== Websites ===
* {{cite web |last1=Bucksch |first1=Alexander |last2=Blonder |first2=Benjamin |last3=Price |first3=Charles |last4=Wing |first4=Scott |last5=Weitz |first5=Joshua |last6=Das |first6=Abhiram |title=Cleared Leaf Image Database |url=http://www.clearedleavesdb.org/ |publisher=School of Biology, [[Georgia Institute of Technology]] |access-date=March 12, 2017 |date=2017 |ref={{harvid|Buckach et al|2017}} |archive-date=September 25, 2014 |archive-url=https://web.archive.org/web/20140925043827/http://clearedleavesdb.org/ |url-status=usurped}} * {{cite web |last1=Geneve |first1=Robert |title=Leaf |url=http://dept.ca.uky.edu/PLS220/leafmainpage.pdf |archive-url=https://web.archive.org/web/20160315062623/http://dept.ca.uky.edu/PLS220/leafmainpage.pdf |archive-date=March 15, 2016 |website=PLS 220: Introduction to plant identification |publisher=University of Kentucky: Department of Horticulture}} * {{cite web |last1=Kling |first1=Gary J. |last2=Hayden |first2=Laura L. |last3=Potts |first3=Joshua J. |title=Botanical terminology |url=http://woodyplantstutorial.nres.illinois.edu/ |publisher=[[University of Illinois]], Urbana-Champaign |access-date=March 7, 2017 |date=2005 |ref={{harvid|Kling et al|2005}} |archive-date=March 8, 2017 |archive-url=https://web.archive.org/web/20170308051032/http://woodyplantstutorial.nres.illinois.edu/ |url-status=live}} * {{cite web |last1=de Kok |first1=Rogier |last2=Biffin |first2=Ed |title=The Pea Key: An interactive key for Australian pea-flowered legumes |url=https://www.anbg.gov.au/cpbr/cd-keys/peakey/key/The%20Pea%20Key/Media/Html/index.html |publisher=Australian Pea-flowered Legume Research Group |access-date=March 9, 2017 |date=November 2007 |archive-date=February 26, 2017 |archive-url=https://web.archive.org/web/20170226150100/http://anbg.gov.au/cpbr/cd-keys/peakey/key/The%20Pea%20Key/Media/Html/index.html |url-status=live}} * {{cite web |last1=Kranz |first1=Laura |title=The Vein Patterns of Leaves |url=http://lauraakranz.com/vein-patterns-leaves/ |format=Drawings |access-date=March 5, 2017 |archive-date=March 6, 2017 |archive-url=https://web.archive.org/web/20170306033751/http://lauraakranz.com/vein-patterns-leaves/ |url-status=live}} * {{cite web |last1=Massey |first1=Jimmy R. |last2=Murphy |first2=James C. |title=Vascular plant systematics |url=http://www.ibiblio.org/botnet/glossary/ |website=NC Botnet |publisher=University of North Carolina at Chapel Hill |access-date=January 19, 2016 |date=1996 |archive-date=January 17, 2016 |archive-url=https://web.archive.org/web/20160117025929/http://www.ibiblio.org/botnet/glossary/ |url-status=live}} ** {{cite web |title=Leaves |url=http://www.ibiblio.org/botnet/glossary/a_v.html |access-date=January 19, 2016 |archive-date=July 25, 2016 |archive-url=https://web.archive.org/web/20160725170655/http://www.ibiblio.org/botnet/glossary/a_v.html |url-status=live}}, in {{harvtxt|Massey|Murphy|1996}} * {{cite web |last=Purcell |first=Adam |title=Leaves |url=http://basicbiology.net/plants/physiology/leaves.php |website=Basic Biology |publisher=Adam Purcell |date=January 16, 2016 |access-date=February 17, 2017 |archive-date=April 19, 2015 |archive-url=https://web.archive.org/web/20150419002416/http://basicbiology.net/plants/physiology/leaves.php |url-status=live}} * {{cite web |last1=Simpson |first1=Michael G. |title=Plants of San Diego County, California |url=http://www.sci.sdsu.edu/plants/sdpls/ |publisher=College of Science, [[San Diego State University]] |access-date=March 2, 2017 |ref={{harvid|Simpson|2017}} |archive-date=March 3, 2017 |archive-url=https://web.archive.org/web/20170303044642/http://www.sci.sdsu.edu/plants/sdpls/ |url-status=live}} * {{cite web |title=Florissant Fossil Beds Leaf Key |url=https://www.nps.gov/flfo/learn/education/upload/PlantPackage.pdf |website=[[Florissant Fossil Beds National Monument]] |publisher=[[National Park Service]], [[US Department of the Interior]] |access-date=February 16, 2017 |ref={{harvid|Florissant Leaf Key|2016}} |archive-date=February 16, 2017 |archive-url=https://web.archive.org/web/20170216150109/https://www.nps.gov/flfo/learn/education/upload/PlantPackage.pdf }} * {{cite web |title=Plant Database |url=https://plantdatabase.kpu.ca/plant/search.gsp |publisher=School of Horticulture, [[Kwantlen Polytechnic University]] |access-date=March 9, 2017 |date=2015 |ref={{harvid|Kwantlen|2015}} |archive-date=September 21, 2017 |archive-url=https://web.archive.org/web/20170921023245/http://plantdatabase.kpu.ca/plant/search.gsp }} * {{cite web |title=Angiosperm Morphology |url=http://www.tutorvista.com/content/biology/biology-iii/angiosperm-morphology/angiosperm-morphologyindex.php |publisher=TutorVista |date=2017 |ref={{harvid|Angiosperm Morphology|2017}} |access-date=March 9, 2017 |archive-date=June 21, 2020 |archive-url=https://web.archive.org/web/20200621215228/http://www.tutorvista.com/content/biology/biology-iii/angiosperm-morphology/angiosperm-morphologyindex.php }}
;Glossaries * {{cite web |last1=Hughes |first1=Colin |title=The virtual field herbarium |url=http://herbaria-old.plants.ox.ac.uk/vfh/about/ |publisher=[[Oxford University Herbaria]] |access-date=March 4, 2017 |ref={{harvid|Hughes|2017}} |archive-url=https://web.archive.org/web/20170305113254/http://herbaria-old.plants.ox.ac.uk/vfh/about/ |archive-date=March 5, 2017 }} ** {{cite web |title=Plant Characteristics |url=http://herbaria-old.plants.ox.ac.uk/vfh/image/index.php?glossary=show |access-date=March 4, 2017 |format=Glossary |ref={{harvid|Oxford herbaria glossary|2017}} |archive-url=https://web.archive.org/web/20170305034525/http://herbaria-old.plants.ox.ac.uk/vfh/image/index.php?glossary=show |archive-date=March 5, 2017 }}, in {{harvtxt|Hughes|2017}} * {{cite web |title=Glossary of botanical terms |url=http://www.kew.org/science/tropamerica/neotropikey/families/glossary.htm#P |website=Neotropikey |publisher=Royal Botanic Gardens, Kew |access-date=February 18, 2017 |ref={{harvid|Neotropikey|2017}} |archive-date=January 21, 2017 |archive-url=https://web.archive.org/web/20170121214009/http://www.kew.org/science/tropamerica/neotropikey/families/glossary.htm#P |url-status=live}} * {{cite web |title=Illustrated glossary of leaf shapes |url=http://plants.ifas.ufl.edu/education/images/GlossaryLeafShapes.pdf |publisher=Center for Aquatic and Invasive Plants, [[Institute of Food and Agricultural Sciences]], University of Florida |access-date=January 8, 2020 |date=2009 |archive-date=January 10, 2020 |archive-url=https://web.archive.org/web/20200110130658/http://plants.ifas.ufl.edu/education/images/GlossaryLeafShapes.pdf |url-status=live}} * {{cite web |title=Leafshapes |url=https://www.donsgarden.co.uk/leafshapes/ |website=Donsgarden |access-date=January 9, 2020 |archive-date=February 4, 2016 |archive-url=https://web.archive.org/web/20160204160841/http://www.donsgarden.co.uk/leafshapes }} {{refend}}
==External links== {{commons category multi|Leaves|Leaf veins}}{{wiktionary|leaf|position = }} * {{Cite EB1911|wstitle=Leaf|volume=15|first= Alfred Barton |last= Rendle |author-link=Alfred Barton Rendle|page=322–329|short=x }} * {{Cite Americana |wstitle=Leaves |volume=XVII |last=Ingersoll |first=Ernest |author-link=Ernest Ingersoll |short=1}}
{{Botany}} {{Authority control}}
[[Category:Leaves| ]] [[Category:Plant anatomy]] [[Category:Plant morphology]] [[Category:Plant physiology]] [[Category:Photosynthesis]]