Relationships within and among species of the holoparasitic genus Hyobanche (Orobanchaceae) inferred from ISSR banding patterns and nucleotide sequences

The systematic relationships of four species in the South African holoparasitic genus Hyobanche were examined using inter-simple sequence repeat (ISSR) banding patterns and nucleotide sequence data from nuclear ribosomal ITS regions and the plastid gene rbcL. Ordination of ISSR data revealed discrete groups, although H. glabrata and H. rubra were indistinguishable. Phylogeny reconstructions based on ISSR and ITS data were congruent and depicted relationships where H. atropurpurea and H. sanguinea form a clade with Pi. glabrata and H. rubra as their sister group. In contrast, the rbcL tree revealed a topology where Pi. atropurpurea was sister to a clade that included the other three species. The combination of molecular, morphological, and biogeographical data suggest two alternative hypotheses: (1) that floral evolution has progressed from galeate hirsute corolla tubes to straight glabrous tubes as represented by Pi. sanguinea, H. glabrata (intermediate morphology), and Pi. rubra, respectively; or (2) the intermediate floral morphology and distribution of H. glabrata reveal a hybrid origin of this species with H. sanguinea and H. rubra as progenitors.