Phylogenetic and population genetic studies in the genus Streptocarpus Lindl. (Gesneriaceae DC.)

[摘要] Streptocarpus Lindl. (Gesneriaceae DC.) is a genus of herbaceous plants containingapproximately 160 species, of which the majority occur in Africa and Madagascar. They arelargely restricted to shaded and moist habitats such as primary forest and rock outcrops. Thegenus contains considerable morphological variation, with subgenus Streptocarpella containingcaulescent species and subgenus Streptocarpus mostly consisting of acaulescent growth forms,mainly the unifoliates, plurifoliates and rosulates. Preliminary molecular analyses conductedusing nuclear ITS sequence data suggested that subgenus Streptocarpus evolved in tropicalcentral Africa, before radiating in several independent waves into southern Africa.Streptocarpus has therefore only recently spread into South Africa. Amongst the South Africanspecies, 11 morphologically similar species were identified as being closely related, togetherforming the Cape primrose clade, based on the analysis of nuclear ITS sequence data. However,these analyses only contained a few South African species, and the ITS data did not provideenough resolution of relationships within this clade.In this study nuclear and chloroplast sequence data as well as nuclear microsatellite data weretherefore employed to unravel the complex relationships amongst the South AfricanStreptocarpus species. The analyses indicate that 16 rosulate, palynologically similar species(S. primulifolius, S. rexii, S. johannis, S. baudertii, S. modestus, S. formosus, S. gardenii,S. lilliputana, the S. cyaneus complex [S. cyaneus, S. parviflorus, S. fenestra-dei, S. kunhardtiiand S. roseo-albus], S. floribundus, S. aylae and S. kentaniensis), the core Cape primrosespecies, are closely related, while five unifoliate/plurifoliate, palynologically more variablespecies (S. denticulatus, S. dunnii, S. pusillus, S. rimicola and S. bolusii) consistently emergedas more distantly related to the core Cape primrose species. However, the positions of a furtherten species (S. meyeri, S. montigena, S. fanniniae, S. caeruleus, S. longiflorus, S. polyanthus,S. saundersii, S. porphyrostachys, S. grandis and S. vandeleurii) were more complex in theanalyses, indicating that hybridization has played a role in their evolution. Five of these species(S. meyeri, S. montigena, S. fanniniae, S. caeruleus and S. longiflorus) are, however,palynologically homogenous and rosulates, and therefore are probably more closely related tothe core Cape primrose species, while the other five (S. polyanthus, S. saundersii,S. porphyrostachys, S. grandis and S. vandeleurii) are unifoliates/plurifoliates that arepalynologically more heterogenous, and are probably more distantly related to the core Capeprimrose species.Amongst the core Cape primrose species, S. primulifolius emerged as being ancestral or havinghybridized with many of the other species, while the S. cyaneus complex forms ageographically and genetically more isolated group. However, evolutionary relationshipsamongst these species were to a certain extent obscured by incomplete lineage sorting causedby limited interpopulation gene flow, frequent hybridization and rapid speciation. The analysesconfirmed that the Pondoland Centre forests constitute important Pleistocene refugia, andrevealed some of the historical migration routes along which the species had radiated.

[发布机构] Stellenbosch University