FRUIT STRUCTURE OF THE GENUS PYRENACANTHA HOOK (ICACINACEAE) IN SOUTHERN AFRICA

Fruit development and structure of the three southern African species of Pyrenacantha were examined by scanning electron microscopy and ligh t microscopy. Fruits of Pyrenacantha are laterally compressed drupes, with a pubescent outer surface. Their shape varies from more-or-less s pherical in P. kaurabassana to ovate in P. scandens and P. grandiflora . Those of P. grandiflora ripen to yellow-grey, of P. kaurabassana to orange, and of P. scandens to a cream colour. The exocarp is one-cell- layered and develops solely from the outer epidermis of the ovary wall . The outer portion of the mesocarp is parenchymatous with vascular bu ndles and cells containing druse crystals of calcium oxalate, whereas a sclerified stone (endocarp sensu lato) develops from the inner porti on. A one-cell-layered parenchymatous endocarp (sensu stricto) develop s from the inner epidermis of the ovary wall. Endocarpal processes tak e their origin from clusters of initial cells in the mesophyll parench yma next to the inner epidermis, and eventually project deep into the locule and seed. The presence of stomata on the surface of the process es, suggests that in addition to enlarging the surface area of the end ocarp and seed, they may facilitate gas exchange between pericarp and seed. Micro-sculpturing of the surface of the endocarpal processes is of taxonomic significance at the species level. The outer surface of t he mature stone is extensively pitted in a species specific pattern.