seedcoat

The seed coat, or testa, is the protective outer layer of a seed. It develops from the integuments of the ovule after fertilization and encloses the embryo and, in many seeds, the endosperm. In angiosperms the coat often comprises an outer epidermal layer (exotesta) and an inner layer (endotesta) that may be lignified or sclerenchymatous; some seeds have a simpler, thinner coating or multiple parenchymatous layers. Pigments, suberin, lignin, and tannins can give the coat color, hardness, and drought resistance.

The seed coat serves several functions. It provides mechanical protection against damage and pathogens and helps limit water loss. It also governs water uptake during germination; in many species a thick, water-impermeable coat enforces physical dormancy, which may require scarification or stratification to permit germination. In addition to protection and dormancy control, the coat can influence seed dispersal and survival through surface textures, colors, and structures that interact with animals, wind, or soil. The coat is often pierced by openings such as the micropyle, hilum, or other pores that relate to pollen entry and germination.

Variation exists across plant groups. The seed coat is derived from the ovule’s integuments in both gymnosperms and angiosperms, and its exact structure and thickness reflect ecological adaptations to drying, temperature, and predation. In agriculture and seed technology, coat properties are manipulated through scarification, chemical treatments, or stratification to improve germination, storage, and vigor.