{{Short description|Stalk attaching a leaf to a plant}} {{For|the narrow waist of some hymenopteran insects|Petiole (insect anatomy)}} thumb|right|200px|Leaf of ''Pyrus calleryana'' with petiole
In botany, the '''petiole''' ({{IPAc-en|ˈ|p|iː|t|i|.|oʊ|l|,_|ˈ|p|ɛ|t|i|-}}), commonly known as the '''leaf stem''' or '''leaf stalk''', is the stalk that attaches the leaf to the twigs, branches or stems of a plant. The terms petiolate and apetiolate are applied, respectively, to leaves with and without petioles.
==Description== thumb|Harvested rhubarb petioles with leaf blades attached [[Image:Acacia koa with phyllode between the branch and the compound leaves.JPG|thumb|right|220px|''Acacia koa'' with phyllode between the branch and the compound leaves]] [[File:繁花薯豆 Elaeocarpus multiflorus 20220911103816 01.jpg|thumb|x200px|Pulvini at both ends of the petioles of ''Elaeocarpus multiflorus'' ]] The petiole is a stalk that attaches a leaf to the rest of a plant.<ref name="Beentje-2010">{{cite book |last=Beentje |first=H. |title=The Kew plant glossary |publisher=Kew Publishing |year=2010 |isbn=9781842464229 |location=London}}</ref>{{rp|87}}<ref name="Mauseth-2003">{{cite book |last=Mauseth |first=James D |title=Botany: An Introduction to Plant Biology |publisher=Jones & Bartlett Learning |year=2003 |isbn=0-7637-2134-4}}</ref>{{rp|171}} In some species, it is able to twist the leaf to face the sun, thus optimizing its exposure to sunlight.<ref name="Capon-2022" /><ref name="TAFE NSW" />
In petiolate leaves, the leaf stalk may be long (as in the leaves of celery and rhubarb) or short (e.g. basil). When completely absent, the blade attaches directly to the stem and is said to be sessile or apetiolate. Subpetiolate leaves have an extremely short petiole and may appear sessile.<ref name="Mauseth-2003" />{{rp|157}} The broomrape family, Orobanchaceae, is an example of a taxon in which the leaves are always sessile.<ref name="Stace-2010">{{cite book|last=Stace|first=C. A.|author-link = Stace, C. A.|year=2010|title=New Flora of the British Isles|edition=Third|publisher=Cambridge University Press|location = Cambridge, U.K.| isbn=9780521707725}}</ref>{{rp|639}} In some other plant groups, such as the speedwell genus ''Veronica'', petiolate and sessile leaves may occur in different species.<ref name="Stace-2010" />{{rp|584}}
In the grasses (Poaceae), the leaves are apetiolate, but the leaf blade may be narrowed at the junction with the leaf sheath to form a pseudopetiole, as in ''Pseudosasa japonica''.<ref name="Heywood-2007">{{cite book|first1=V.H.|last1=Heywood|first2=R.K.|last2=Brummitt|first3=A.|last3=Culham|first4=O.|last4=Seberg|year=2007|title= Flowering plant families of the world|publisher=Firefly Books|location=New York|isbn=9781554072064}}</ref>{{rp|391}}
In plants with compound leaves, the leaflets are attached to a continuation of the petiole called the rachis.<ref name="Beentje-2010"/>{{rp|98}} Each leaflet may be attached to the rachis by a short stalk called the petiolule.<ref name="Beentje-2010"/>{{rp|87}} There may be swollen regions at either end of the petiole known as pulvina (singular = pulvinus)<ref name="Beentje-2010"/>{{rp|97}} that are composed of a flexible tissue that allows leaf movement. Pulvina are common in the bean family Fabaceae and the prayer plant family Marantaceae. A pulvinus on a petiolule is called a pulvinulus.
In some plants, the petioles are flattened and widened to become phyllodes (also known as phyllodia or cladophylls) and the true leaves may be reduced or absent. Thus, the phyllode comes to serve the functions of the leaf. Phyllodes are common in the genus ''Acacia'', especially the Australian species, at one time put in ''Acacia'' subgenus ''Phyllodineae''.
In ''Acacia koa'', the phyllodes are leathery and thick, allowing the tree to survive stressful environments. The petiole allows partially submerged hydrophytes to have leaves floating at different depths, the petiole being between the node and the stem.
==Etymology== 'Petiole' comes from Latin petiolus, or 'little foot', 'stem', an alternative diminutive of 'pes', 'foot'. The regular diminutive 'pediculus' is also used for 'foot stalk'.
==Uses== In plants such as rhubarb (''Rheum rhabarbarum''), celery (''Apium graveolens''), artichokes, and cardoons (''Cynara cardunculus''), the petioles are cultivated as edible crops. The petiole of rhubarb grows directly from the rhizome and produces the leaf at its end. Botanically, it is categorized as a vegetable but, culinarily, it is more often used as a fruit.<ref>{{cite book |last=Foust |first=Clifford M. |title=Rhubarb: The Wondrous Drug |publisher=Princeton University Press |year=1992 |isbn=0-691-08747-4 |location=Princeton}}</ref><ref>{{Cite web |title=High Altitude Rhubarb |url=https://highaltituderhubarb.com/ |url-status=live |archive-url=https://web.archive.org/web/20220530212249/https://highaltituderhubarb.com/ |archive-date=30 May 2022 |access-date=9 June 2022 |website=Highaltituderhubarb.com}}</ref>
==See also== *Hyponastic response *Pedicel *Stipule
==References== <references> <ref name="Capon-2022">{{cite book |last1=Capon |first1=Brian |title=Botany for Gardeners: An Introduction to the Science of Plants |date=July 2022 |publisher=Timber Press |location=Portland |isbn=978-1643261430 |edition=4 |url=https://www.hachettebookgroup.com/titles/brian-capon/botany-for-gardeners-fourth-edition/9781643261430/?lens=timber-press |access-date=2023-09-27 |archive-date=2023-09-27 |archive-url=https://web.archive.org/web/20230927235634/https://www.hachettebookgroup.com/titles/brian-capon/botany-for-gardeners-fourth-edition/9781643261430/?lens=timber-press |url-status=live }}</ref>
<ref name="TAFE NSW">{{cite web |title=Parts of a leaf |url=https://sielearning.tafensw.edu.au/floristry/References/Parts%20of%20a%20leaf.htm |website=TAFE NSW |publisher=New South Wales Government |access-date=2020-06-22 |archive-date=2020-06-23 |archive-url=https://web.archive.org/web/20200623084019/https://sielearning.tafensw.edu.au/floristry/References/Parts%20of%20a%20leaf.htm |url-status=dead}}</ref> </references>
==External links== {{commonscat|Petioles|lcfirst=yes}} *{{Cite Collier's|wstitle=Petiole |short=x}}
{{botany}}
{{DEFAULTSORT:Petiole (Botany)}} Category:Leaf morphology