cotyledon (seed leaf) A part of the embryo in a seed plant. The number of cotyledons is an important feature in classifying plants. Among the flowering plants, the class known as Monocotyledoneae have a single cotyledon and Dicotyledoneae have two. Conifers have either two cotyledons, as in Taxus (yews), or five to ten, as in Pinus (pines). In seeds without an endosperm, e.g. garden pea and broad bean, the cotyledons store food, which is used in germination. In seeds showing epigeal germination, e.g. runner bean, they emerge above the soil surface and become the first photosynthetic leaves.

cot·y·le·don / ˌkätlˈēdn/ • n. Bot. an embryonic leaf in seed-bearing plants, one or more of which are the first leaves to appear from a germinating seed.DERIVATIVES: cot·y·le·don·ar·y / -ˈēdnˌerē/ adj.

cotyledon First leaf or pair of leaves produced by the embryo of a flowering plant. Its function is to store and digest food for the embryo plant, and, if it emerges above ground, to photosynthesize for seedling growth. See also dicotyledon; monocotyledon

cotyledon A seed leaf that is borne on a plant embryo. Characteristically there is 1 leaf in the monocotyledons, and 2 leaves in the dicotyledons, but there are exceptions, especially in the latter group.

cotyledon seed-leaf. XVIII. — L. cotylēdon navelwort, pennywort — Gr. kotúlēdṓn applied to various cup-shaped cavities, f. kotúlē hollow, cup.