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monocotyledon
Monocotyledons (〔An Anglo-Latin pronunciation. ''OED:'' "Monocotyledon".〕), also known as monocots, are plants whose seeds typically contain only one embryonic leaf, or cotyledon. They constitute one of the major groups into which flowering plants (or angiosperms) have traditionally been divided, the rest of the flowering plants having two cotyledons and being classed as dicotyledons, or dicots. However, molecular phylogenetic research has shown that the monocots form a monophyletic group – a clade – since they comprise all the descendants of a common ancestor, but that dicots do not form a monophyletic group. Monocots have almost always been recognized as a group, but with various taxonomic ranks and under several different names. The APG III system of 2009 recognises a clade called "monocots" but does not assign it to a taxonomic rank.
According to the IUCN there are 59,300 species of monocots.〔http://cmsdata.iucn.org/downloads/2008rl_stats_tables_all.xls〕 The largest family in this group (and in the flowering plants as a whole) by number of species are the orchids (family Orchidaceae), with more than 20,000 species.〔Peter H. Raven, Ray Franklin Evert & Susan E. Eichhorn. (2005) ''Biology of Plants'', 7th ed., page 459〕 About half as many species belong to the true grasses, Poaceae, who are economically the most important family of monocots: in agriculture the majority of the biomass produced comes from monocots. These include not only major grains (rice, wheat, maize, etc.), but also forage grasses, sugar cane, and the bamboos. Other economically important monocot cultures include various palms (Arecaceae), bananas (Musaceae), gingers and their relatives, turmeric and cardamom (Zingiberaceae) and onions (Amaryllidaceae), which includes such ubiquitously used vegetables as onions and garlic. Additionally, plants cultivated for their blooms are also from the monocot group, notably lilies, daffodils, irises, amaryllis, cannas, bluebells and tulips.
==Description==
The monocots are one of the major divisions of the flowering plants or angiosperms. They have been recognized as a natural group since at least the work of the English botanist John Ray in the 17th century. Modern research based on DNA has confirmed the status of the monocots as a monophyletic group or clade, in contrast to the other historical divisions of the flowering plants, which have had to be substantially reorganized. The name monocotyledons is derived from the traditional botanical name "Monocotyledones", which refers to the fact that most members of this group have one cotyledon, or embryonic leaf, in their seeds. Historically, this feature was used to contrast the monocots with the dicotyledons or dicots which typically have two cotyledons; however modern research has shown that the dicots are not a natural group. From a diagnostic point of view the number of cotyledons is neither a particularly useful characteristic (as they are only present for a very short period in a plant's life), nor is it completely reliable.
Additionally, 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—having three, six, or nine petals. Many monocots also have leaves with parallel veins.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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