(seed leaf) The first leaf or leaves of the embryo in seed plants. In angiosperms the number of cotyledons is an important taxonomic character used to separate the two subclasses Monocotyledonae and Dicotyledonae. In endospermic seeds the cotyledons may be thin and membranous, as in the castor oil seed, but in nonendospermic seeds, e.g. pea, they take over the food-storing functions of the endosperm. Depending on the pattern of germination the cotyledons may remain in the seed (see hypogeal
) or emerge to become the first photosynthetic organs (see epigeal
). Gymnosperms may have several cotyledons.