Rampant non­monophyly of species in Kniphofia Moench (Asphodelaceae) suggests a recent Afromontane radiation

Abstract

The genus Kniphofia, comprising 71 species, has an African­Malagasy distribution, with one species from Yemen. The genus is found predominantly in moist temperate montane grassland and has its centre of diversity in the Drakensberg region of southern Africa. The genus has a complex alpha taxonomy and species relationships are poorly understood. Using a multiple exemplar approach, DNA sequence data from the chloroplast trnT­L spacer and the nuclear internal transcribed spacer region were used in an attempt to resolve phylogenetic relationships. Five cpDNA lineages were recovered, the geographic distributions of which correspond well with previously identified Afromontane centres of diversity and endemism. The data revealed that several morphospecies were non­monophyletic, and this, together with short branch lengths and many identical sequences within each of the five lineages, suggests a recent radiation. We additionally propose that hybridisation and/ or incomplete lineage sorting may also account for this result. The nrITS region was largely uninformative as many taxa and samples had identical sequences. We hypothesise that Kniphofia experienced periods of range expansion, secondary contact and hybridisation during Pleistocene glacial periods, followed by contraction, fragmentation and isolation in montane refugia during the warmer interglacial periods.

Evolution of Asparagus L. (Asparagaceae): Out-of-South-Africa and multiple origins of sexual dimorphism

“…In some cases, such as the genus Kniphofia, all tested species have been shown to be paraphyletic (Ramdhani et al, 2009). The potential explanations for the occurrence of paraphyletic species have attracted much attention (Meimberg et al, 2010;Ramdhani et al, 2009;Rieseberg and Brouillet, 1994). A simple approach is to argue that only monophyletic species should be recognized (Baum and Donoghue, 1995;Mishler and Theriot, 2000), or that the concepts of mono-or paraphyly do not apply to species (Davis and Nixon, 1992).…”

“…These results may be expected, as reviews by Crisp and Chandler (1996) and Funk and Omland (2003) suggest that paraphyletic species may be quite common and indeed their surveys produced rather similar percentages of paraphyletic species (23% of all tested species being paraphyletic). In some cases, such as the genus Kniphofia, all tested species have been shown to be paraphyletic (Ramdhani et al, 2009). The potential explanations for the occurrence of paraphyletic species have attracted much attention (Meimberg et al, 2010;Ramdhani et al, 2009;Rieseberg and Brouillet, 1994).…”

“…Consequently, we currently have no convincing indications of the presence of natural gene flow between closely related species. Lineage sorting is most commonly observed in recently diverged clades, and is often interpreted as a signal for recent radiation (Ramdhani et al, 2009). This might apply in some clades in Asparagus, where the resolution within the species complexes (e.g.…”

“…Two mechanisms are commonly proposed: post-speciation gene flow (e.g., hybridization) and/or lineage sorting (Meimberg et al, 2010;Ramdhani et al, 2009). There is evidence of polyploidy in Asparagus (Jessop, 1966), and although hybrids can be made between some closely related species in the genus, there appear to be sterility barriers among many species (Falavigna et al, 2008;Ito et al, 2008).…”

Phylogeographical Pattern in the Southern African Grass <I>Tenaxia disticha</I> (Poaceae)

“…This seems unlikely, but could be readily tested by common-garden experiments. Secondly, the lack of sequence divergence could be an expression of lineage sorting, as has been postulated in several other southern African taxa (Pleines et al 2009;Ramdhani et al 2009;Ramdhani et al 2010), where the morpho-anatomical divergence may be from a genetically diverse ancestor. However, the lack of phylogenetic structure is not due to conflicting patterns (as would be indicative if the ancestral lineages had different copies of the loci) but lack of sequence divergence.…”