What are cotyledons?

Cotyledons are the embryonic seed leaves present in the seed of a plant, serving as the first leaves to appear during germination and playing a crucial role in early seedling nutrition. These specialized structures store food reserves—primarily proteins, carbohydrates, and lipids—that nourish the developing embryo until the seedling can produce its own food through photosynthesis. In some plants, cotyledons emerge above ground and turn green to photosynthesize (epigeal germination), while in others they remain underground and simply transfer stored nutrients to the growing seedling (hypogeal germination).

The number of cotyledons is a fundamental basis for classifying flowering plants into two major groups: monocotyledons (monocots) have a single cotyledon, as seen in grasses, corn, and lilies, while dicotyledons (dicots) have two cotyledons, as observed in beans, peas, and most broadleaf plants. This distinction affects many other plant characteristics including leaf venation patterns, root systems, and flower structure. Observing cotyledons in germinating seeds—like the two fleshy halves of a bean seed or the single blade-like leaf of a corn seedling—provides immediate insight into the plant's classification and developmental strategy.