Bark Structure and Intergeneric Relationships of Some Southern African Cassinoideae (Celastraceae)

Abstract

At present Cassine in southern Africa is treated in a wide sense (s.l.), including amongst others Allocassine p. p., Cassines. str., Crocoxylon, Elaeodendron, Lauridia, and Mystroxylon. A comparative anatomical study was made of mature bark representing 16 southern African species of Cassine s.l., and the monotypic Allocassine, Hartogiella and Maurocenia (all members of the subfamily Cassinoideae). Six bark types are distinguished on the basis of the type of sclerenchymatous elements in the secondary phloem; presence or absence of styloid crystals, e1astic threads, and sclerified phelloderm; stratified homogeneous phellem; and degree of rhytidome development. These correlate to a considerable extent with the generic subdivision of Cassine s.l. proposed by Loesener (1942) and Robson (1965). On the basis of bark anatomy and other evidence, it is proposed that the circumscription of Cassine be restricted to include only the southern African species C. peragua and C. parvifolia, and possibly Hartogiella. Crocoxylon, Elaeodendron, Lauridia and Mystroxylon should be reinstated or maintained, although with some modification of the originally defined generic limits.