mesotesta

Mesotesta is a botanical term describing the middle layer of the seed coat (testa) in many angiosperms. When present, it sits between the exotesta, the outermost layer, and the endotesta, the innermost layer. The mesotesta develops from tissues linked to the integuments that surround the ovule and can consist of parenchymatous cells or more specialized sclerenchymal tissue, depending on the species.

The presence and structure of the mesotesta vary widely. In some seeds the mesotesta is thin or indistinct, while in others it is well developed and may become lignified, contributing to the overall hardness and durability of the seed coat. This layer can influence seed physiology, including permeability to water and gases, and can play a role in seed dormancy mechanisms.

In botanical descriptions, the terms exotesta, mesotesta, and endotesta are used to differentiate distinct tissue layers of the testa. However, not all seeds display all three layers clearly; in many lineages the mesotesta may be absent or fused with adjacent tissues, and the seed coat is described using fewer terms. The specific anatomy of the mesotesta can be important for systematic and evolutionary studies, as variations in seed coat structure often reflect different ecological strategies.

See also: seed coat, testa, exotesta, endotesta, integument.