Phylogenetic and population genetic studies in the genus Streptocarpus Lindl. (Gesneriaceae DC.)
Date
2008-12
Authors
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Journal ISSN
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Publisher
Stellenbosch : Stellenbosch University
Abstract
Streptocarpus Lindl. (Gesneriaceae DC.) is a genus of herbaceous plants containing
approximately 160 species, of which the majority occur in Africa and Madagascar. They are
largely restricted to shaded and moist habitats such as primary forest and rock outcrops. The
genus contains considerable morphological variation, with subgenus Streptocarpella containing
caulescent species and subgenus Streptocarpus mostly consisting of acaulescent growth forms,
mainly the unifoliates, plurifoliates and rosulates. Preliminary molecular analyses conducted
using nuclear ITS sequence data suggested that subgenus Streptocarpus evolved in tropical
central Africa, before radiating in several independent waves into southern Africa.
Streptocarpus has therefore only recently spread into South Africa. Amongst the South African
species, 11 morphologically similar species were identified as being closely related, together
forming 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 provide
enough resolution of relationships within this clade.
In this study nuclear and chloroplast sequence data as well as nuclear microsatellite data were
therefore employed to unravel the complex relationships amongst the South African
Streptocarpus 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. kunhardtii
and S. roseo-albus], S. floribundus, S. aylae and S. kentaniensis), the core Cape primrose
species, are closely related, while five unifoliate/plurifoliate, palynologically more variable
species (S. denticulatus, S. dunnii, S. pusillus, S. rimicola and S. bolusii) consistently emerged
as more distantly related to the core Cape primrose species. However, the positions of a further
ten 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 the
analyses, 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 to
the core Cape primrose species, while the other five (S. polyanthus, S. saundersii,
S. porphyrostachys, S. grandis and S. vandeleurii) are unifoliates/plurifoliates that are
palynologically more heterogenous, and are probably more distantly related to the core Cape
primrose species.
Amongst the core Cape primrose species, S. primulifolius emerged as being ancestral or having
hybridized with many of the other species, while the S. cyaneus complex forms a
geographically and genetically more isolated group. However, evolutionary relationships
amongst these species were to a certain extent obscured by incomplete lineage sorting caused
by limited interpopulation gene flow, frequent hybridization and rapid speciation. The analyses
confirmed that the Pondoland Centre forests constitute important Pleistocene refugia, and
revealed some of the historical migration routes along which the species had radiated.
Description
Thesis (PhD (Botany and Zoology))—-Stellenbosch University, 2008.
Keywords
Streptocarpus, Phylogenetics, Population genetics, Gesneriaceae, Theses -- Botany, Dissertations -- Botany