Systematic studies on the subtribe Disinae (Orchidaceae)
Doctoral Thesis
1982
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University of Cape Town
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Abstract
The subtribe Disinae (Orchidaceae) has been revised over its whole distribution range (Sub-Saharan Africa and including the Yemen, Madagascar and Reunion). One hundred and sixty-five species arranged in 5 genera are recognized. Three new subspecies, 12 new species, 18 new series, 8 new sections and 7 new subgenera are described. Where deemed necessary, the species are grouped into subgenera, sections and series to indicate their interrelationships. Distribution maps were prepared for all the species, and the ecology and nomenclature of every species is discussed, while many are illustrated. The revision is based primarily on morphological data. In complex situations the variation is displayed by scatter diagrams. Both artificial and natural keys are reduced for the large genus Disa. The grouping of the sections and genera is analysed both by computer-based phenetic analyses, using the BOLAID program, and by Hennigian phylogenetic studies. The eventual classification is based on the phylogenetic scheme. The groupings produced by the two methods are compared and discussed and the theoretical bases of classifications are briefly discussed. The phytogeography of the subtribe is analysed in some detail. Centres of endemism are delimited, and their interrelationships are analysed, together with the patterns of species and above-species richness. The history of the subtribe is analysed using the taxonomic rank of the disjunctions between the centres as an indication of the age of the disjunctions. The postulated history is then compared to modern ideas on the recent African palaeoenvironments. On this evidence it is suggested that the Disinae migrated northwards from an early diversification in southern Africa, and that the present patterns have been much influenced by climatic changes in the last 50 000 years.
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Bibliography: pages 126-138.
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Linder, H. 1982. Systematic studies on the subtribe Disinae (Orchidaceae). University of Cape Town.