The Generic Position of Protorhus namaquensis Sprague (Anacardiaceae): Evidence from Fruit Structure

Abstract

In Protorhus namaquensis the outer epidermis of the ovary forms the exocarp. At maturity it is uniseriate and consists of palisade-like parenchyma cells and modified stomata (MS). A cuticle, extensive cutinization of the outer cell walls and starch also characterize the exocarp. The mesocarp develops from the ground tissue of the ovary wall and includes an outer zone of large-celled tanniniferous parenchyma, secretory ducts associated with some of the vascular bundles, prismatic crystals of calcium oxalate and brachysclereids. The inner epidermis of the ovary undergoes successive periclinal divisions whose derivatives form the mature endocarp. It is stratified and tetraseriate, comprising successive layers (from mesocarp inwards) of crystalliferous cells, brachysclereids, osteosclereids and macrosclereids. The morphology of the female flower, and the fruit structure of P. namaquensis are compared with that of P. longifolia (lectotype of the genus and only other African species) and species of Ozoroa. We present abundant evidence that P. namaquensis should be associated with some members of the genus Ozoroa , rather than with P. longifolia. The new combination, Ozoroa namaquensis (Sprague) Von Teichman & Van Wyk, is proposed. Characters of the perianth and pericarp, inter alia the occlusion of the pores of most MS, are considered adaptations of the species to its harsh semi-desert habitat.