Leaf anatomy of the southern African Icacinaceae and its taxonomic significance

Abstract

Leaf structure of the three southern African genera of Icacinaceae was examined by light and scanning electron microscopy. Diagnostic characters include the stoma and trichome type, and lamina characters, such as mucilage cells, pectic warts and ‘unidentified cell inclusions’. In southern Africa both Cassinopsis Sond. and Pyrenacantha Hook. have cyclocytic stomata, as opposed to the anomocytic type of Apodytes E. Mey. Ex Arn. The presence of a stomatal ridge in A. dimidiata is a useful character in separating this species from the other two southern African members of this genus. A peristomal rim in Cassinopsis tinifolia Harv. and its absence in C. ilicifolia (Hochst.) Kuntze allow the separation of these two species. The indumentum of Pyrenacantha consists of simple (unmodified), ‘globular’ and ‘uncinate’ trichomes, whereas that of Apodytes and Cassinopsis consists of simple hairs. Mucilage cells were found only in members of Apodytes. Intercellular, predominantly wart-like pectic protuberances are present in the mesophyll of mature leaf samples of A. geldenhuysii Van Wyk & Potgieter and Cassinopsis. Small, irregularly shaped, yellowish cell inclusions were found subepidermally to the abaxial epidermis in C. ilicifolia. Their chemical composition and function (if any) is still unknown.