EVOLUTION OF 2 SERPENTINE ENDEMIC TAXA IN MPUMALANGA

Two taxa endemic to serpentine soils in Mpumalanga, Berkheya rehmannii Thell. var. rogersiana Thell. and B. coddii Rossl. (Asteraceae) were selected to investigate the mode of evolution of serpentine endemics u sing enzyme electrophoresis, Morphological studies based on herbarium material suggested that the serpentine endemic B. rehmannii var. roger siana is probably closely related to B. rehmannii Thell. var. rehmanni i which does not grow on serpentine. The electrophoretic investigation revealed high genetic identities between all taxa studied. However, t he presence of unique alleles in var. rogersiana and large differences in allele frequencies between var. rogersiana and var, rehmannii sugg est that these taxa are genetically distinct, that there is little or no gene flow between them and that they could be a progenitor-derivati ve pair. These data and the distribution data suggested that var, roge rsiana is probably not neo-endemic nor palaeo-endemic but somewhere in between and B. coddii is probably palaeo-endemic and that they arose during independent evolutionary events. Thus, palaeo-endemism probably exists in the elements of the serpentine flora in Mpumalanga that wer e studied and both serpentine-tolerance and nickel accumulation have e volved more than once.