A taxonomic reassessment of the subtribe Asciepiadinae (Asclepiadaceae) in Southern Africa : Vol. 2.

Abstract

This study extends an earlier M.Sc. research project on the narrow-leaved species of the genus Asclepias L. (30 species) to cover the entire subtribe Asclepiadinae sensu K. Schum. in southern Africa- (182 species in 23 genera). Two genera (Eustegia R. Br. and Pentarrhinum E. Mey.) are revised and then removed from this tribe. The remaining 177 species and 21 genera form the focus of this thesis, whose principal objectives are to reevaluate the taxonomic and evolutionary significance of various macro, micro and chemical characters and then use them to produce a classification that, more closely, reflects the overall similarity and phylogeny of the taxa involved. Species and genera are recircumscribed based on the wealth of data that has come to light since the subtribe was last revised by N.E. Brown (1907-1908) some 90 years ago. This process was supplemented by extensive field work, observations on pollination and reproductive biology, ecology, biogeography, conservation and ethnobotany. The majority of this thesis consists of a compilation of 17 papers, 12 of these published and most, but not all, of the remainder in preparation for press. Two of these papers form the bulk of the taxonomy. The first deals with what was the genus Asclepias in southern Africa. The genus is now believed to be confined to the Americas. The • Botswana, Lesotho, Namibia, South Africa and Swaziland. southern African species have diverse origins and are partitioned into 7 genera, one of them (Gomphocarpus R. Br.) resurrected, two of them (Aidomene Stopp and Aspidonepsis Nicholas & Goyder) expanded and four of them (Paulforstera, Sigridia, Bruynsia and Pachyacris) described as new. Gomphocarpus is divided into two subgenera and Aidomene into four subgenera. Three new species are also described. The second paper investigates the bulk of most of the remaining genera. Kanahia R. Br., Cordylogyne E. Mey. and Fanninia Harv. remain as is. Xysmalobium R. Br., previously a genus of 19 species in southern Africa, is reduced to three species in two subgenera. Trichocodon is segregated off from Pachycarpus E. Mey. as a new genus. While two species, previously placed in Xysmalobium, are added to Pachycarpus, but placed in the new subgenus Parapodiopsis. Parapodium E. Mey. is reduced from three to two species and Periglossum Decne. is reduced from five to three species, one of them newly described. Woodia Schltr. and Stenostelma Schltr. are both considerably expanded, mainly with species previously housed in Xysmalobium), and the former divided into two subgenera. The third paper briefly looks at the Schizoglossum E. Mey., Miraglossum Kupicha and Aspidoglossum E. Mey. Some changes are suggested but, as further work is needed, none are formalised. As a corollary to the taxonomy, secondary metabolite profiles of 38 species and 17 genera were done using Thin layer Chromatography. The results sometimes confirmed morphological patterns and sometimes were at odds with them. A trend from simple profiles to more complex profiles seems to echo the suspected phylogeny of the genera within this sub tribe. Some species and genera have greater chemical diversity than others and secondary metabolites are shown to vary considerably in different parts of a single plant. As a supplement to the above work or because they are cited elsewhere in the dissertation, published papers dealing with floral structure, the asclepiadaceous work of Rudolf Schlechter, as well as miscellaneous works in the tribe Stapelieae, are also given.