endotesta

Endotesta is the inner layer of the seed coat, derived from the inner integument of the ovule. It lies inside the exotesta, the outer seed coat, and together these layers form the protective covering around the seed. During ovule development, the inner integument’s epidermal layer gives rise to the endotesta, while the outer integument forms the exotesta. In many seeds the endotesta is a discrete layer, but its thickness and degree of differentiation vary among species.

Structure and variation: The endotesta can consist of one or several cell layers. Its cell walls may be thickened and sclerenchymatous in some taxa, providing additional rigidity, while in others it is thin or poorly differentiated. In certain species, the endotesta is very reduced or effectively absent, and the seed coat is dominated by the exotesta. In other seeds, the endotesta and exotesta may be closely appressed or even fused, giving a continuous, single-appearing seed coat.

Function and significance: The endotesta contributes to mechanical protection of the seed and can influence properties such as texture, permeability, and coloration. It can also bear pigments or other structures that affect seed appearance. From a botanical perspective, the presence, absence, thickness, and cellular characteristics of the endotesta are important diagnostic features in seed anatomy and are used in taxonomic and phylogenetic studies to differentiate taxa.

Terminology: Endotesta is sometimes referred to as the inner testa or inner seed coat, with exotesta being the outer layer. The seed coat as a whole is formed by these integument-derived components and may vary considerably across plant groups.