Phylogeny and Conservation of African Violets (Saintpaulia: Gesneriaceae): New Findings Based on Nuclear Ribosomal 5S Non-Transcribed Spacer Sequences

The phylogeny, biogeography, and conservation prioritization of African violet taxa (Saintpaulia: Gesneriaceae) in East Africa was investigated using parsimony analysis of nucleotide sequences from the 5S nuclear ribosomal DNA (nrDNA) non-transcribed spacer (5S-NTS). Although in substantial agreement with a previous phylogenetic analysis of nrDNA internal transcribed spacer (ITS) sequences, the present study of the faster evolving 5S-NTS locus identified two new, major lineages, the Nguru Mountains and Usambara Mountains/lowland clades. The genetic diversity within the basal-most Saintpaulia clade, present in the Nguru, Uluguru, and Ukaguru Mountains, was underscored by addition of an Uluguru Mountains collection of Saintpaulia pusilla. Previous studies based on ITS included only a single individual of Saintpaulia goetzeana, here represented by two disjunct populations. These accessions were genetically divergent and separated from Saintpaulia pusilla by long branches. However, no support could be found for an earlier suggestion that the Uluguru Mountains represent the ancestral area for the genus. Indeed, the Nguru Mountains hold two to three of the four major Saintpaulia clades identified, and our conclusion is that this region should be given the highest priority for conservation of African violet genetic and morphological diversity. An additional prioritization suggestion derives from the finding that Saintpaulia taxa from Kenyan lowlands form a discrete subclade within the poorly-resolved Usambaras/lowland clade, providing at least one clearly recognizable, geographically distinct, and reproductively isolated lineage of what may have recently constituted only metapopulational variation.