A taxonomic revision of Southern African Cassinoideae (Celastraceae)

Abstract

The primary object of this study was to provide a taxonomic account of the southern African Cassinoideae. The Cassinoideae is one of at least seven subfamilies in the morphologically diverse family Celastraceae. Cassinoideae consists of ± 21 genera worldwide of which eight genera, treated here, occur in southern Africa. There has been considerable diversity of opinion regarding the delimitation and recognition of genera among the species of Cassine L. s. l. Many authors advocated smaller, more homogeneous genera, while others preferred to treat Cassine in a wide sense, so as to include parts of Allocassine N. Robson, Crocoxylon Eckl. & Zeyh., Elaeodendron Jacq., Lauridia Eckl. & Zeyh. and Mystroxylon Eckl. & Zeyh. New evidence from morphology and anatomy, as well as other sources, has accomplished a better understanding of generic limits in the southern African Cassinoideae. A classification of the southern African Cassinoideae, based on all available evidence, 1s presented. In this treatment, believed to be the closest possible to a natural classification, eight genera are recognized. Five genera, Cassine s. str., Allocassine, Maurocenia Mill., Lauridia and a new genus, Robsonodendron, are considered endemic to southern Africa. Two genera, Mystroxylon and Pleurostylia, comprise one species each in southern Africa but have an unknown number of taxa in the Mascarenes, Asia and Australasia. Elaeodendron is the only cosmopolitan genus, with about 30 species worldwide. All the African species of Elaeodendron are treated. The present concept of Cassine s. str. requires many name reversals to the original basionym under Elaeodendron. The genus Robsonodendron is newly described to accommodate two southern African species. Hartogiella Codd and Crocoxylon are sunk under Cassine and Elaeodendron respectively. This study extends the work on the southern African species of Cassine presented as an M.Sc. thesis in 1990. The dissertation is a compilation of 13 papers published in or submitted for publication in various scientific journals. A traditional morphologictaxonomic approach was employed to revise the southern African Cassinoideae. Taxonomic decisions, however, were based on detailed study ofpalynology, leaf, wood and bark anatomy, general morphology and field observations, as well as a study of moz;e than 4000 herbarium specimens from various herbaria. In the taxonomic treatment, each species is described, accompanied by nomenclature and notes on its distribution and ecology. Several nomenclatural problems are discussed. A proposal for the conservation of the name Cassine barbara L. with a new type according to new provisions of the International Code for Botanical Nomenclature (Greuter et al. 1994) is presented. All specimens examined are listed. Three colour illustrations are included. Keys to the genera and species are provided