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[[Image:Hemerocallis_longituba.jpg|thumb|''[[Hemerocallis]]'' flower, with three flower parts in each whorl]]
[[Image:Wheat_close-up.JPG|thumb|[[Wheat]], an economically important monocot]]
The '''monocotyledons''' or '''monocots''' are a group of [[flowering plant]]s, (angiosperms) dominating great parts of the earth. Monocots comprise the majority of agricultural plants in terms of biomass produced. There are between 50,000 and 60,000 [[species]] within this group; according to IUCN there are 59,300 species.[http://www.redlist.org/info/tables/table1]
The largest family in this group by number of species (and in the flowering plants) are the orchids (usually taken to be the family [[Orchidaceae]], but sometimes treated at the [[rank (botany)|rank]] of order), with about twenty thousand species. These have very complex (and striking) flowers, adapted for highly specific [[insect]] [[pollination]].
The economically most important family in this group (and in the flowering plants) are the [[Poaceae|grass]]es, family [[Poaceae]] (Gramineae). These include all the true [[grains]] ([[rice]], [[wheat]], [[maize]], etc.), the pasture grasses and the [[bamboo]]s. This family of the true grasses have evolved in another direction, becoming highly specialized for wind pollination. Grasses produce much smaller flowers, which are gathered in highly visible plumes ([[inflorescence]]s). A further noteworthy, and economically important family is the palm family [[Arecaceae]] (Palmae).
==Name, characters==
The name monocotyledons is derived from the traditional botanical name ''Monocotyledones'', which derives from the fact that most members of this group have one [[cotyledon]], or embryonic leaf, in their [[seed]]s. This as opposed to the traditional [[Dicotyledon]]es, which typically have two cotyledons. From a diagnostic point of view the number of cotyledons is neither a particularly handy (as they are only present for a very short period in a plant's life), nor totally reliable character.
Nevertheless, monocots are a distinctive group.<ref>{{cite journal | title=Monocot relationships: an overview | url=http://www.amjbot.org/cgi/content/full/91/10/1645 | journal=American Journal of Botany | year=2004 | volume=91 | pages=1645-1655 | author=Mark W. Chase }}</ref> One of the most noticeable traits is that a monocot's flower is [[trimerous]], with the flower parts in threes or in multiples of three. For example, a monocotyledon's flower typically has three, six, or nine petals. Many monocots also have [[leaf|leaves]] with parallel veins.
[[Image:Hypoxis.jpg|thumb|right|''Hypoxis decumbens'' [[Carolus Linnaeus|L.]] with a typical monocot perigone and parallel leaf venation]]
==Morphology, compared to the (former) dicotyledons==
The traditionally listed differences between monocotyledons and dicotyledons are as follows. This is a broad sketch only, not invariably applicable, as there are a number of exceptions. The differences indicated are more true for [[monocots]] versus [[eudicots]], as per the [[APG II system]]:
'''Flowers:''' In monocots, flowers are trimerous (number of flower parts in a whorl in threes) while in dicots the flowers are tetramerous or pentamerous (flower parts are in fours or fives).
'''Pollen:''' In monocots, pollen has one [[furrow]] or [[pore]] while dicots have three.
'''Seeds:''' In monocots, the embryo has one [[cotyledon]] while the embryo of the dicot has two.
'''Stems:''' In monocots, [[vascular bundle]]s in the [[Plant stem|stem]] are scattered, in dicots arranged in a ring.
'''Roots:''' In monocots, roots are [[adventitious]], while in dicots they develop from the [[radicle]].
[[Image:Onion_slice.jpg|thumb|right|slice of onion, showing parallel veins]]
'''Leaves:''' In monocots, the major leaf [[veins]] are [[Parallel (geometry)|parallel]], while in dicots they are reticulate.
However, these differences are not hard and fast: some monocots have characteristics more typical of dicots, and vice-versa. This is in part because "dicots" are a [[paraphyletic]] group with respect to monocots, and some dicots may be more closely related to monocots than to other dicots. In particular, several early-branching lineages of "dicots" share "monocot" characteristics, suggesting that these are not defining characters of monocots. When monocots are compared to [[eudicots]], the differences are more concrete.
==Taxonomy==
The monocots are considered to form a [[monophyletic]] group arising early in the history of the [[flowering plant]]s. The earliest fossils presumed to be monocot remains date from the [[Cretaceous|early Cretaceous]] period.
Taxonomists have considerable latitude in naming this group, as the monocots are a group above the rank of family. Article 16 of the ''[[ICBN]]'' allows either a [[descriptive botanical names|descriptive name]] or a name formed from the name of an included family.
[[Image:Monocot_vs_dicot_crop_Pengo.jpg|thumb|Grass sprouting on left (a monocot), showing a single cotyledon. Compared to a dicot (right)]]
Historically, the monocotyledons were named:
* [[Monocotyledoneae]] in the [[de Candolle system]] and the [[Engler system]].
* [[Monocotyledones]] in the [[Bentham & Hooker system]] and the [[Wettstein system]]
* class [[Liliopsida]] in the [[Takhtajan system]] and the [[Cronquist system]].
* subclass [[Liliidae]] in the [[Dahlgren system]] and the [[Thorne system (1992)]].
* [[clade]] [[monocots]] in the [[APG system]] and the [[APG II system]].
Each of the systems mentioned above use their own internal taxonomy for the group. The monocotyledons are famous as a group that is extremely stable in its outer borders (it is a well-defined, coherent group), while in its internal taxonomy is extremely unstable (historically no two authoritative systems have agreed with each other on how the monocotyledons are related to each other).
==References and external links==
<references />
* Chase MW, Soltis DE, Soltis PS, Rudall PJ, Fay MF, Hahn WJ, Sullivan S, Joseph J, Molvray M, Kores PJ, Givnish TJ, Sytsma KJ, Pires JC (2000). Higher-level systematics of the monocotyledons: An assessment of current knowledge and a new classification. In: Wilson KL, Morrison DA, eds. ''Monocots: Systematics and Evolution.''. CSIRO, Melbourne. 3-16. ISBN 0-643-06437-0
*[http://tolweb.org/tree?group=Monocotyledons&contgroup=Euangiosperms Tree of Life Web Project: Monocotyledons]
*{{cite web |url=http://www.redlist.org/info/tables/table1 |title=Numbers of threatened species by major groups of organisms (1996–2004) |accessdate=2006-12-15 |publisher=International Union for Conservation of Nature and Natural Resources |work= }}
[[Category:Botanical nomenclature]]
[[Category:Plant taxonomy]]
[[Image:Wheat_close-up.JPG|thumb|[[Wheat]], an economically important monocot]]
The '''monocotyledons''' or '''monocots''' are a group of [[flowering plant]]s, (angiosperms) dominating great parts of the earth. Monocots comprise the majority of agricultural plants in terms of biomass produced. There are between 50,000 and 60,000 [[species]] within this group; according to IUCN there are 59,300 species.[http://www.redlist.org/info/tables/table1]
The largest family in this group by number of species (and in the flowering plants) are the orchids (usually taken to be the family [[Orchidaceae]], but sometimes treated at the [[rank (botany)|rank]] of order), with about twenty thousand species. These have very complex (and striking) flowers, adapted for highly specific [[insect]] [[pollination]].
The economically most important family in this group (and in the flowering plants) are the [[Poaceae|grass]]es, family [[Poaceae]] (Gramineae). These include all the true [[grains]] ([[rice]], [[wheat]], [[maize]], etc.), the pasture grasses and the [[bamboo]]s. This family of the true grasses have evolved in another direction, becoming highly specialized for wind pollination. Grasses produce much smaller flowers, which are gathered in highly visible plumes ([[inflorescence]]s). A further noteworthy, and economically important family is the palm family [[Arecaceae]] (Palmae).
==Name, characters==
The name monocotyledons is derived from the traditional botanical name ''Monocotyledones'', which derives from the fact that most members of this group have one [[cotyledon]], or embryonic leaf, in their [[seed]]s. This as opposed to the traditional [[Dicotyledon]]es, which typically have two cotyledons. From a diagnostic point of view the number of cotyledons is neither a particularly handy (as they are only present for a very short period in a plant's life), nor totally reliable character.
Nevertheless, monocots are a distinctive group.<ref>{{cite journal | title=Monocot relationships: an overview | url=http://www.amjbot.org/cgi/content/full/91/10/1645 | journal=American Journal of Botany | year=2004 | volume=91 | pages=1645-1655 | author=Mark W. Chase }}</ref> One of the most noticeable traits is that a monocot's flower is [[trimerous]], with the flower parts in threes or in multiples of three. For example, a monocotyledon's flower typically has three, six, or nine petals. Many monocots also have [[leaf|leaves]] with parallel veins.
[[Image:Hypoxis.jpg|thumb|right|''Hypoxis decumbens'' [[Carolus Linnaeus|L.]] with a typical monocot perigone and parallel leaf venation]]
==Morphology, compared to the (former) dicotyledons==
The traditionally listed differences between monocotyledons and dicotyledons are as follows. This is a broad sketch only, not invariably applicable, as there are a number of exceptions. The differences indicated are more true for [[monocots]] versus [[eudicots]], as per the [[APG II system]]:
'''Flowers:''' In monocots, flowers are trimerous (number of flower parts in a whorl in threes) while in dicots the flowers are tetramerous or pentamerous (flower parts are in fours or fives).
'''Pollen:''' In monocots, pollen has one [[furrow]] or [[pore]] while dicots have three.
'''Seeds:''' In monocots, the embryo has one [[cotyledon]] while the embryo of the dicot has two.
'''Stems:''' In monocots, [[vascular bundle]]s in the [[Plant stem|stem]] are scattered, in dicots arranged in a ring.
'''Roots:''' In monocots, roots are [[adventitious]], while in dicots they develop from the [[radicle]].
[[Image:Onion_slice.jpg|thumb|right|slice of onion, showing parallel veins]]
'''Leaves:''' In monocots, the major leaf [[veins]] are [[Parallel (geometry)|parallel]], while in dicots they are reticulate.
However, these differences are not hard and fast: some monocots have characteristics more typical of dicots, and vice-versa. This is in part because "dicots" are a [[paraphyletic]] group with respect to monocots, and some dicots may be more closely related to monocots than to other dicots. In particular, several early-branching lineages of "dicots" share "monocot" characteristics, suggesting that these are not defining characters of monocots. When monocots are compared to [[eudicots]], the differences are more concrete.
==Taxonomy==
The monocots are considered to form a [[monophyletic]] group arising early in the history of the [[flowering plant]]s. The earliest fossils presumed to be monocot remains date from the [[Cretaceous|early Cretaceous]] period.
Taxonomists have considerable latitude in naming this group, as the monocots are a group above the rank of family. Article 16 of the ''[[ICBN]]'' allows either a [[descriptive botanical names|descriptive name]] or a name formed from the name of an included family.
[[Image:Monocot_vs_dicot_crop_Pengo.jpg|thumb|Grass sprouting on left (a monocot), showing a single cotyledon. Compared to a dicot (right)]]
Historically, the monocotyledons were named:
* [[Monocotyledoneae]] in the [[de Candolle system]] and the [[Engler system]].
* [[Monocotyledones]] in the [[Bentham & Hooker system]] and the [[Wettstein system]]
* class [[Liliopsida]] in the [[Takhtajan system]] and the [[Cronquist system]].
* subclass [[Liliidae]] in the [[Dahlgren system]] and the [[Thorne system (1992)]].
* [[clade]] [[monocots]] in the [[APG system]] and the [[APG II system]].
Each of the systems mentioned above use their own internal taxonomy for the group. The monocotyledons are famous as a group that is extremely stable in its outer borders (it is a well-defined, coherent group), while in its internal taxonomy is extremely unstable (historically no two authoritative systems have agreed with each other on how the monocotyledons are related to each other).
==References and external links==
<references />
* Chase MW, Soltis DE, Soltis PS, Rudall PJ, Fay MF, Hahn WJ, Sullivan S, Joseph J, Molvray M, Kores PJ, Givnish TJ, Sytsma KJ, Pires JC (2000). Higher-level systematics of the monocotyledons: An assessment of current knowledge and a new classification. In: Wilson KL, Morrison DA, eds. ''Monocots: Systematics and Evolution.''. CSIRO, Melbourne. 3-16. ISBN 0-643-06437-0
*[http://tolweb.org/tree?group=Monocotyledons&contgroup=Euangiosperms Tree of Life Web Project: Monocotyledons]
*{{cite web |url=http://www.redlist.org/info/tables/table1 |title=Numbers of threatened species by major groups of organisms (1996–2004) |accessdate=2006-12-15 |publisher=International Union for Conservation of Nature and Natural Resources |work= }}
[[Category:Botanical nomenclature]]
[[Category:Plant taxonomy]]