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

[摘要] English: In southern Africa, the Poaceae include 194 genera and 967 species andintraspecific taxa, of which 329 are endemic, 847 indigenous and 115naturalised (Gibbs RusseIl 1985).The classification, at present, is based on non-Kranz leaf anatomy andmorphology of the spikelet (Clayton & Renvoize 1986). The Arundinoideae aredifficult to characterize because they are heterogeneous with numerous isolatedor weakly linked genera, whose relationships are highly conjectural.Most of the species of Merxmuellera and Karroochloa were previouslypart of the genus Danthonia (Nees & Essenbeck 1841, Steudel 1855, Durand &Schinz 1895). A number of species of Danthonia were recently allocated to thenew genera Karroochloa and Merxmuellera (Conert & Turpe 1969, Conert1971). For a long time, the genus Schismus was regarded as very closelyrelated to Danthonia and more recently to the genus Karroochloa. OneSchsimus species was originally assigned to Danthonia (Conert & Turpe 1974).The genus Karroochloa consists of four species, two perennials and twoannuals. At present, 20 species are recognised in Merxmuellera, 18 are fromsouthern Africa and two species are from the mountains of Madagascar (Barker1994). The type species of Schismus, namely S. barbatus grows in southernAfrica 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 inthis genus are all endemic to South Africa.The high level of genetic variability allows the grasses to take advantageof new habitats (Ehrendorf 1980). In this investigation, the species M. strictaand M. disticha revealed wide distribution patterns which overlap and mayindicate that these two species are of hybrid origin and, therefore, well adaptedto a wide range of climatic conditions, soil types, rainfall and altitude.In the genus Merxmuellera, morphologically distinct groups of species can beidentified. The genera Karroochloa and Schismus form monophyletic groupingsand the distance data indicates that morphologically, Schismus lies betweenMerxmuellera and Karroochloa.Previous cytogenetic studies have indicated that the genus Merxmuellerahas basic chromosome numbers of six and seven (Spies et al. 1990). In thisinvestigation no indications of a basic chromosome number of seven was foundand Merxmuellera is thus considered to have a basic chromosome number ofsix. This genus reveals high ploidy levels that indicate an old polyploid complexwas dealt with. In the case of the other two genera Karroochloa and Schismusyoung polyploid complexes were dealt with. Only diploids were studiedalthough there are reports on polyploids (Spies & Du Plessis 1986b, 1988).The chromosome behaviour indicates that M. stricta and M. distichacould be of hybrid origin.Embryo sac studies of nine species indicate that all these species are ofthe Polygonum-type and that Merxmuellera indicates a variety of embryo sacformations. Karroochloa, Merxmuellera and Schism us can be distinguishedclearly on embryo sac structure.The peR based RAPD procedure was applied to resolve and investigatethe three genera and their species. A strong relationship between theMerxmuellera species, M. ruie, M. decora and M. lupulina was clearly illustratedby the RAPD data.The ITS analysis indicated conflicting clustering of some species as wellas expected clustering of other species. Ultimately the following argument isapplicable: gene trees may not necessarily represent species trees (Doyle1992).In this study the percentage lacking data in the combined analysis wastoo large to be used in the combined analysis. Therefore all the data sets wereanalysed separately and then compared to each other to make the finalconclusions in this thesis.The close relationships between M. ruie, M. decora and M. lupulina areevident. Therefore, it is suggested that the three species should be combinedinto one species and be regarded as a polyploid complex, rather than threeseparate species.It is clear that all the summer rainfall Merxmuellera species are relatedand the most practical systematic treatment appears to be upholding only twospecies namely M. stricta and M. disticha.The validity of the species S. pleuropogon must be investigated becauseonly one specimen, the type specimen, was collected and described by Stapf(1916) and no further specimens were found. Therefore, S. pleuropogon mayhave become extinct or it may have been a once-off hybrid.Although the genus Karroochloa consists of four species, the finalanalysis indicates that these species are very closely related and that theannual status of K. schismoides should be carefully investigated. Such aninvestigation will indicate whether Karroochloa includes four of three species.

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