# Sclereid

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{{Short description|Plant tissue type}}
thumb|Fresh mount of a sclereid in a banana fruit
'''Sclereids''' are a reduced form of [sclerenchyma](/source/sclerenchyma) cells with highly thickened, lignified [cellular walls](/source/cell_wall) that form  small bundles of durable layers of tissue in most [plant](/source/plant)s.<ref name="RayEic">Evert, Ray F; Eichhorn, Susan E. Esau's Plant Anatomy: Meristems, Cells, and Tissues of the Plant Body: Their Structure, Function, and Development. Publisher: Wiley-Liss 2006. {{ISBN|978-0471738435}}</ref> The presence of numerous sclereids form the cores of [apple](/source/apple)s and produce the gritty texture of [guava](/source/guava)s.

Although sclereids are variable in  shape, the cells are generally isodiametric, prosenchymatic, forked, or elaborately branched. They can be grouped into bundles, can form complete tubes located at the periphery, or can occur as single cells or small groups of cells within [parenchyma](/source/parenchyma) tissues. An isolated sclereid cell is known as an [idioblast](/source/idioblast). Sclereids are typically found in the [epidermis](/source/epidermis), [ground tissue](/source/ground_tissue), and [vascular tissue](/source/vascular_tissue).<ref name=PlantAnat>{{cite book |title=Anatomy of Seed Plants |series=Plant Anatomy |edition=2nd |author=Katherine Esau |publisher=John Wiley & Sons |page=72 |year= 1977 |isbn=0-471-24520-8}}</ref>

The term "sclereid" was introduced by [Alexander Tschirch](/source/Alexander_Tschirch) in 1885.<ref>Tschirch, A. (1885). Beiträge zur Kenntnis des mechanischen Gewebesystems der Pflanzen. ''Pringsheims Jahrbücher für Wissenschaftliche Botanik'' XVI: 303-335.</ref>

==Origin==

Sclereids are created through belated [sclerosis](/source/sclerenchyma) of [parenchyma](/source/parenchyma) cells or can arise from sclereid primordia that are individualized early in development. Sclerification typically involves thickening of the cell wall, increasing rigidity. In the [phloem](/source/phloem), when tissue ceases to function in conduction cells may begin sclerification. In vascular tissue, sclereids will develop from [cambial](/source/Cambium) and procambial cells.<ref name=Under>{{cite book |title= Understanding Plant Anatomy |author= S. R. Mishra |publisher= Discovery Publishing House |year= 2009 |isbn= 9788183564571 |page= 105}}</ref>

==Stem sclereids==

In the vascular region of the stem of ''[Hoya carnosa](/source/Hoya_carnosa)'', a column of sclereids can be found, and in the [pith](/source/pith) of stems of ''[Hoya](/source/Hoya_(plant))'' and ''[Podocarpus](/source/Podocarpus)'' groups of sclereids can be found. These are sclereids with thick cell walls and numerous [pits](/source/Pit_(botany)), resembling adjacent parenchyma cells. This resemblance suggests that these sclereids are originally [parenchyma](/source/parenchyma) cells, but are so sclerified that they are now sclereid cells rather than parenchyma cells. These sclereids are an example of brachysclereids, or stone cells.<ref name=PlantAnat/>

==Leaf sclereids==
thumb|right|Long tapered sclereids supporting a leaf edge in ''Dionysia kossinskyi''

Leaves contain a variety of types of sclereids. In the [mesophyll](/source/mesophyll), two distinct sclereid structures are found. Sclereids in a diffuse pattern are dispersed throughout the leaf tissue, and sclereids in a terminal pattern are concentrated about the tips of [leaf veins](/source/leaf_veins). Sclereid formations in leaves include the branched sclereids of ''[Trochodendron](/source/Trochodendron)'', the columnar sclereids of ''[Hakea](/source/Hakea)'', and the hair-like trichosclereids that branch into air chambers within the leaves of the [water lily](/source/Nymphaea) and [yellow pond lily](/source/Nuphar). Sclereids can also form part of or the entire epidermis of [foliar](/source/foliar) structures such as the clove scales of ''[Allium sativum](/source/Allium_sativum)''.<ref name=PlantAnat/>

Especially interesting are the sclereids in [olive](/source/Olea_europaea) leaves. They are typically {{convert|1|mm|abbr=on}} in length and are thus named fiberlike sclereids. These sclereids permeate the mesophyll as a dense mat.<ref>{{cite book |series= University Botany |title= Gymnosperms, Plant Anatomy, Genetics, Ecology |volume= 2 |author= S. M. Reddy, S. J. Chary |publisher= New Age International |year= 2003 |isbn= 9788122414776 |page= 105}}</ref> During sclerification these fiberlike sclereid cells can increase by several hundred times their original size, compared to other parenchyma cells that only increase by two or three times.<ref name=Under/>

==Fruit sclereids==

Sclereids in fruits vary in form and use. In [pear](/source/pear)s, sclereids form concentric clusters that grow about earlier formed sclereids. These pear sclereids, as well as sclereids within [quince](/source/quince) fruit, often form [bordered pits](/source/Pit_(botany)) when the cell wall increases in thickness during sclerification. In [apple](/source/apple)s, layers of elongated sclereids form the [endocarp](/source/endocarp) that encloses the seeds.<ref name=PlantAnat/>

==Seed sclereids==

The hardening of seed coats during ripening often occurs through sclerification, when the secondary cell walls are thickened in the epidermis and below the epidermis. [Leguminous](/source/Legume) seeds are examples of such sclerification. Larger sclereids form columns in the epidermis of [pea](/source/Pisum), [bean](/source/Phaseolus), and [soybean](/source/Glycine_(genus)) seeds, and bone-shaped osteosclereids occur beneath the epidermis. In the seed coats of [coconut](/source/Cocos_nucifera)s, sclereids possess numerous bordered pits.<ref name=PlantAnat/> These larger macrosclereids found in seed coats are of protodermal origin.<ref name=Under/>

==References==
{{Reflist}}

==Further reading==
* Chrispeels MJ, Sadava DE. (2002). ''Plants, Genes and Crop Biotechnology''. Jones and Bartlett Inc. {{ISBN|0-7637-1586-7}}.
* {{cite book | last = Mauseth | first = James D. | year = 2012 | title = Botany: An Introduction to Plant Biology | edition = 5th | location = Sudbury, MA | publisher = Jones and Bartlett Learning | isbn = 978-1-4496-6580-7}}
* Moore, Randy; Clark, W. Dennis; and Vodopich, Darrell S. (1998). ''Botany'' (3rd ed.). McGraw-Hill. {{ISBN|0-697-28623-1}}.

{{Biological tissue}}

{{DEFAULTSORT:Sclereid}}
Category:Plant anatomy
Category:Plant cells
Category:Tissues (biology)

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Adapted from the Wikipedia article [Sclereid](https://en.wikipedia.org/wiki/Sclereid) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Sclereid?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.