(Gr. monos: alone, single; kotylêdon: cavity, hollow) One of the two classes of flowering plants (see Anthophyta), distinguished by having one seed leaf (cotyledon) within the seed. The monocotyledons generally have parallel leaf veins, scattered vascular bundles within the stems, and flower parts in threes or multiples of three. Monocotyledon species include some crop plants (e.g. cereals, onions, fodder grasses), ornamentals (e.g. tulips, orchids, lilies), and a very limited number of trees (e.g. the palms). Cf. Dicotyledonae.