cotyledon [key], in botany, a leaf of the embryo of a seed. The embryos of flowering plants, or angiosperms, usually have either one cotyledon (the monocots) or two (the dicots). Seeds of gymnosperms, such as pines, may have numerous cotyledons. In some seeds the cotyledons are flat and leaflike; in others, such as the bean, the cotyledons store the seed's food reserve for germination and are fleshy. In most plants the cotyledons emerge above the soil with the seedling as it grows. They differ in form from the true leaves.
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