A taxonomic reassessment of the subtribe Asciepiadinae (Asclepiadaceae) in Southern Africa : Vol. 2.
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Date
1999
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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.
Description
Thesis (Ph.D.)-University of Durban-Westville, 1999.
Keywords
Theses--Botany., Asclepiadaceae--Africa, Southern., Plants--Classification.