what is cotyledon

A cotyledon is the first leaf or one of the first pair or whorl of leaves developed by the embryo of a seed plant or of some lower plants. Cotyledons are a significant part of the embryo within the seed of a plant, and are defined as "the embryonic leaf in seed-bearing plants, one or more of which are the first to appear from a germinating seed". The number of cotyledons present is one characteristic used by botanists to classify the flowering plants (angiosperms). Species with one cotyledon are called monocotyledonous ("monocots"). Plants with two embryonic leaves are termed dicotyledonous ("dicots") . Cotyledons help supply the nutrition a plant embryo needs to germinate and become established as a photosynthetic organism and may themselves be a source of nutritional reserves or may aid the embryo in metabolizing nutrition stored elsewhere in the seed. In the case of dicot seedlings whose cotyledons are photosynthetic, the cotyledons are functionally similar to leaves. However, true leaves and cotyledons are developmentally distinct. Cotyledons are formed during embryogenesis, along with the root and shoot meristems, and are therefore present in the seed prior to germination. True leaves, however, are formed later.