Genetic variation among and within Lithops species in Namibia

The dwarf succulent genus Lithops is endemic to Southern Africa and of considerable conservation concern. Species delimitation is often problematic and based mainly on leaf morphology, which is strongly associated with habitat. Relationships between taxa and populations in Namibia were studied with amplified fragment length polymorphisms using 44 wild Lithops populations representing 15 species and 23 taxa. Four primer pairs produced 92 polymorphic bands in the 223 samples. Expected heterozygosity (H) within taxa ranged from 0.086 to 0.450. Genetic and geographic distances were correlated according to a Mantel test. Analysis of molecular variance showed only 23% variation among the 15 investigated species. Genetic differentiation and structuring were investigated with a principal coordinate analysis, a neighbour-joining and a Bayesian phylogeny, a Bayesian clustering analysis and a discriminant analysis of principal components. In all five analyses, L. optica and L. herrei, which differ only in flower colour, clustered closely together and are here combined under L. optica. The morphologically similar species L. amicorum and L. karasmontana clustered together. Lithops amicorum is therefore reduced to subspecific level: L. karasmontana subsp. amicorum, comb. nov. Subspecific taxa overlapped to a large extent except in L. karasmontana where 13% of the variability resided among subspecies, whereas the nominal subspecies differed from subsp. bella and subsp. eberlanzii; the latter two could not be separated and are here combined under L. karasmontana subsp. bella.