sarcotesta

Sarcotesta is a fleshy outer layer of the seed coat (testa) formed from the outer integument of the ovule in certain plant groups. It surrounds the seed and is typically soft, sometimes vividly colored, and may be mucilaginous or fibrous. The sarcotesta is distinct from harder seed coats such as sclerotesta and from inner seed coverings; in some species the line between sarcotesta and aril is blurred because a fleshy aril may originate from the funiculus or integument and be functionally similar to a sarcotesta.

Development and structure: During ovule development the outer integument thickens and differentiates into a fleshy tissue, which constitutes the sarcotesta. In many plants this tissue is the visible, edible-like layer that encases the seed.

Function and ecology: The primary ecological role of the sarcotesta is to aid dispersal by attracting animals that consume the tissue and disperse the seed in their droppings or by removing the seed from the surrounding fruit material. It can also provide moisture and some protection to the developing seed.

Distribution and examples: The sarcotesta is best known in certain gymnosperms such as Ginkgo biloba, where a conspicuous fleshy outer layer surrounds the seed, and in several other taxa where a similar fleshy seed coat occurs. In angiosperms and some gymnosperms the precise anatomy and origin can vary, and in some cases the tissue is referred to as an aril rather than a sarcotesta.

Terminology: The term sarcotesta derives from Greek roots meaning flesh and seed coat. Botanists may use sarcotesta and aril with overlapping meanings depending on the taxa and the developmental origin of the fleshy layer.