Phylogeny of the genera Karroochloa, Merxmuellera and Schismus (Poaceae)

English: In southern Africa, the Poaceae include 194 genera and 967 species and intraspecific taxa, of which 329 are endemic, 847 indigenous and 115 naturalised (Gibbs RusseIl 1985). The classification, at present, is based on non-Kranz leaf anatomy and morphology of the spikelet (Clayton & Renvoize 1986). The Arundinoideae are difficult to characterize because they are heterogeneous with numerous isolated or weakly linked genera, whose relationships are highly conjectural. Most of the species of Merxmuellera and Karroochloa were previously part of the genus Danthonia (Nees & Essenbeck 1841, Steudel 1855, Durand & Schinz 1895). A number of species of Danthonia were recently allocated to the new genera Karroochloa and Merxmuellera (Conert & Turpe 1969, Conert 1971). For a long time, the genus Schismus was regarded as very closely related to Danthonia and more recently to the genus Karroochloa. One Schsimus species was originally assigned to Danthonia (Conert & Turpe 1974). The genus Karroochloa consists of four species, two perennials and two annuals. At present, 20 species are recognised in Merxmuellera, 18 are from southern Africa and two species are from the mountains of Madagascar (Barker 1994). The type species of Schismus, namely S. barbatus grows in southern Africa as well as in northern Africa and Europe. The closely related species, S. arabicus also occurs in the Northern Hemisphere and the other three species in this genus are all endemic to South Africa. The high level of genetic variability allows the grasses to take advantage of new habitats (Ehrendorf 1980). In this investigation, the species M. stricta and M. disticha revealed wide distribution patterns which overlap and may indicate that these two species are of hybrid origin and, therefore, well adapted to a wide range of climatic conditions, soil types, rainfall and altitude. In the genus Merxmuellera, morphologically distinct groups of species can be identified. The genera Karroochloa and Schismus form monophyletic groupings and the distance data indicates that morphologically, Schismus lies between Merxmuellera and Karroochloa. Previous cytogenetic studies have indicated that the genus Merxmuellera has basic chromosome numbers of six and seven (Spies et al. 1990). In this investigation no indications of a basic chromosome number of seven was found and Merxmuellera is thus considered to have a basic chromosome number of six. This genus reveals high ploidy levels that indicate an old polyploid complex was dealt with. In the case of the other two genera Karroochloa and Schismus young polyploid complexes were dealt with. Only diploids were studied although there are reports on polyploids (Spies & Du Plessis 1986b, 1988). The chromosome behaviour indicates that M. stricta and M. disticha could be of hybrid origin. Embryo sac studies of nine species indicate that all these species are of the Polygonum-type and that Merxmuellera indicates a variety of embryo sac formations. Karroochloa, Merxmuellera and Schism us can be distinguished clearly on embryo sac structure. The peR based RAPD procedure was applied to resolve and investigate the three genera and their species. A strong relationship between the Merxmuellera species, M. ruie, M. decora and M. lupulina was clearly illustrated by the RAPD data. The ITS analysis indicated conflicting clustering of some species as well as expected clustering of other species. Ultimately the following argument is applicable: gene trees may not necessarily represent species trees (Doyle 1992). In this study the percentage lacking data in the combined analysis was too large to be used in the combined analysis. Therefore all the data sets were analysed separately and then compared to each other to make the final conclusions in this thesis. The close relationships between M. ruie, M. decora and M. lupulina are evident. Therefore, it is suggested that the three species should be combined into one species and be regarded as a polyploid complex, rather than three separate species. It is clear that all the summer rainfall Merxmuellera species are related and the most practical systematic treatment appears to be upholding only two species namely M. stricta and M. disticha. The validity of the species S. pleuropogon must be investigated because only one specimen, the type specimen, was collected and described by Stapf (1916) and no further specimens were found. Therefore, S. pleuropogon may have become extinct or it may have been a once-off hybrid. Although the genus Karroochloa consists of four species, the final analysis indicates that these species are very closely related and that the annual status of K. schismoides should be carefully investigated. Such an investigation will indicate whether Karroochloa includes four of three species.