Monocotyledons (/ˈmɒnɵˈkɒtɪˈliːdən/), also known as monocots, are one of the major groups into which flowering plants (or angiosperms) are divided. Traditionally, the rest of the flowering plants were classed as dicotyledons, or dicots. Monocot seedlings typically have one cotyledon (seed-leaf), in contrast to the two cotyledons typical of dicots. Modern research using molecular phylogenetic methods has shown that the monocots form a monophyletic group – a clade – since they comprise all the descendants of a common ancestor. Dicots, by contrast, do not form a monophyletic group.
Monocots have been recognized as a group at various taxonomic ranks, and under various names (see below). The APG III system of 2009 recognises a clade called "monocots" but does not assign it to a taxonomic rank.
Comparison of a monocot and dicot sprouting. Note that the visible part of the monocot plant (left) is actually the first true leaf produced from the meristem; the cotyledon itself remains within the seed.
According to the IUCN there are 59,300 species of monocots. 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. In agriculture the majority of the biomass produced comes from monocots. The true grasses, family Poaceae (Gramineae), are the most economically important family in this group. These include all the true grains (rice, wheat, maize, etc.), the pasture grasses, sugar cane, and the bamboos. True grasses have evolved to become highly specialised for wind pollination. Grasses produce much smaller flowers, which are gathered in highly visible plumes (inflorescences). Other economically important monocot families are the palm family (Arecaceae), banana family (Musaceae), ginger family (Zingiberaceae) and the amaryllis family (Amaryllidaceae), which includes such ubiquitously used vegetables as onions and garlic.