cotyledon

A cotyledon is a part of the embryo in a seed plant, commonly referred to as a seed leaf. It is one of the first structures to form as the seed develops and plays a key role in the early life of the seedling. In flowering plants, cotyledons provide nutrients to the young plant and may serve as the first photosynthetic organs after germination, depending on the species.

There are two main types of cotyledons based on the plant’s classification. Monocotyledons, or monocots, have a single cotyledon. In these seeds, the cotyledon often functions as a nutrient transfer tissue, sometimes called the scutellum, which draws nourishment from the endosperm to the embryo. The visible first leaves after germination are formed later and are protected by additional structures such as the coleoptile.

Dicotyledons, or dicots, have two cotyledons. These seed leaves typically store nutrients and may become the first photosynthetic leaves after germination, depending on the germination type. In epigeal germination, the cotyledons rise above the soil and commonly become green and photosynthetic; in hypogeal germination, they remain below ground and may not photosynthesize for a while.

Cotyledons develop during embryogenesis and are distinguished by their role in nutrient storage and early seedling establishment. They are a traditional diagnostic feature in seed plant taxonomy, providing essential clues about a species’ germination biology and early growth strategy.