Monocotyledons or monocots are a group of flowering plants usually ranked as a class and once called the Monocotyledoneae. This taxonomic grouping is now named Liliopsida after the type genus, Lilium. Flowering plants not included in the Liliopsida are dicotyledons or dicots. These two broad groups are distinguished by the number of cotyledons, or embryonic leaves, in their seeds: dicots have two, and monocots have one.
The monocots are considered to form a monophyletic group which evolved from an early dicot. The earliest fossils presumed to be monocot remains date from the early Cretaceous period. The largest modern monocot family is the Orchidaceae (orchids), plants which have specialized in insectpollination. For this reason many species of orchids produce very complex flower structures. The second largest and perhaps more notable family, the Poaceae (true grasses), have evolved in another direction, becoming highly specialized for wind pollination. Grasses produce small, generally inconspicuous flowers.
In addition to having but one embryonic cotyledon, the monocots are set apart within the flowering plants by a number of other specializations. See how to distinguish a monocot from a dicot.
The APG II classification System, developed by the Angiosperm Phylogeny Group, recognizes ten orders of monocots and two families not yet assigned to any order, and divides these among the Base Monocots and Commelinids:
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 0643064370
Tree of Life Web Project: Monocotyledons (http://tolweb.org/tree?group=Monocotyledons&contgroup=Euangiosperms)
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