SYSTEMATICS AND EVOLUTION OF THE DISA-DRACONIS COMPLEX (ORCHIDACEAE)

The systematic status of Disa draconis (L.f.) Sw. is revised following extensive field studies of population variation in the Western Cape, South Africa Principal component and cluster analyses revealed clear d istinctions between populations from sandplain, semi-arid and montane environments. Diagnostic characters were found in each of the populati on clusters indicating the existence of a species complex, rather than a single taxon as in the current taxonomy. We propose, therefore, tha t the name D. draconis (L.f.) Sw. be restricted to the individuals of the sandplain populations from which the type was collected. We reinst ate an earlier name, Disa harveiana Lindl., to describe the montane po pulations which possess several autapomorphic characters. We also show that the geographical variation in spur length and flowering time wit hin this species can be partitioned into two geographically distinct s ubspecies: D. harveiana subsp. harveiana and D. harveiana subsp. longi calcarata Johnson & Linder. The populations from the semi-arid Karoo r egion were recognized as a distinct new species, Disa karooica Johnson & Linder, on the basis of their peculiar petal structure. A cladistic analysis indicated that the three species forming the D. draconis com plex form a monophyletic and relatively specialized lineage within Dis a sect. Coryphaea. The revised classification also has important conse rvation implications as D. draconis, previously considered a common sp ecies, is now restricted to a few highly threatened populations on the west coast near Cape Town. (C) 1995 The Linnean Society of London