epicotyl

An epicotyl is the portion of a seedling's shoot axis that lies above the cotyledons and below the first true leaves. It is part of the embryo axis in flowering plants and develops into the aerial shoot after germination. The epicotyl contains the shoot apical meristem and, as development proceeds, gives rise to the stem and the first leaves.

In typical dicot germination, the hypocotyl—the segment between the root and the cotyledons—pulls the seed coat and cotyledons above the soil, after which the epicotyl elongates to form the rest of the shoot and the first true leaves. In monocots, the shoot is protected by a coleoptile and the epicotyl region develops into the part of the shoot that bears the first true leaves once the protective sheath is breached.

Functionally, the epicotyl serves as the continuation of the shoot axis, coordinating the emergence of the aboveground parts and the establishment of photosynthetic organs. Its growth is influenced by hormonal signals and environmental cues, including light and temperature. In agriculture and horticulture, epicotyl length and vigor are used as indicators of seedling vigor and can affect transplant success and lodging risk.