Comparative anatomical studies in five southern African species of Crassula: II. Structure of the leaf and the occurrence of transfer cells

Crassula dependens Bolus, C. inanis Thunb., C. lanceolata Endl., C. natalensis Schonl. and C. peploides Harv. were collected in Lesotho and South Africa and their anatomical features studied. The leaves of Crassula are typically fleshy, ovoid to elliptic. The unifacial mesophyll consists of large round, thin-walled, chlorophyll-containing parenchyma cells. The palisade tissue is absent. The stomata are always surrounded by a girdle of three subsidiary cells, except in the aquatic taxon, C. inanis, in which vestigial stomata are surrounded by two subsidiary cells and the pore often fails to develop. Electron microscopy reveals the occurrence of transfer cells not previously recorded for the genus. Minor leaf vein transfer cells of the B-type occur in all the five species of Crassula. Stem transfer cells associated with the phloem occur in C. dependans.