Exochaenium clavatum subsp. stella-palustre (Gentianaceae—Exaceae), a new subspecies from Zambia
Exochaenium clavatum subsp. stella-palustre is here described as a new subspecies from Zambia. It is characterized by its relatively small size (20 cm tall), leaves massed at the base of the stem and oriented downwards, a single, bright yellow flower, and a calyx wing broadest at the middle. Furthermore, this new taxon was collected in a dambo, in contrast to the inundated lakeshores where E. clavatum subsp. clavatum typically occurs. A key distinguishing the two subspecies is provided.
Secrets to survival – how the tiny annual Sebaea manages to persist in a changing environment
Phylogenetic relationships of the mycoheterotrophic genus Voyria and the implications for the biogeography of Gentianaceae
Back to Gondwanaland: can ancient vicariance explain (some) Indian Ocean disjunct plant distributions?
Oceans, or other wide expanses of inhospitable environment, interrupt present day distributions of many plant groups. Using molecular dating techniques, generally incorporating fossil evidence, we can estimate when such distributions originated. Numerous dating analyses have recently precipitated a paradigm shift in the general explanations for the phenomenon, away from older geological causes, such as continental drift, in favour of more recent, long-distance dispersal (LDD). For example, the ‘Gondwanan vicariance’ scenario has been dismissed in various studies of Indian Ocean disjunct distributions. We used the gentian tribe Exaceae to reassess this scenario using molecular dating with minimum (fossil), maximum (geological), secondary (from wider analyses) and hypothesis-driven age constraints. Our results indicate that ancient vicariance cannot be ruled out as an explanation for the early origins of Exaceae across Africa, Madagascar and the Indian subcontinent unless a strong assumption is made about the maximum age of Gentianales. However, both the Gondwanan scenario and the available evidence suggest that there were also several, more recent, intercontinental dispersals during the diversification of the group.
Novel microsatellite loci for Sebaea aurea (Gentianaceae) and cross-amplification in related species
• Premise of the study: Microsatellite loci were developed in Sebaea aurea (Gentianaceae) to investigate the functional role of diplostigmaty (i.e., the presence of additional stigmas along the style). • Methods and Results: One hundred seventy-four and 180 microsatellite loci were isolated through 454 shotgun sequencing of genomic and microsatellite-enriched DNA libraries, respectively. Sixteen polymorphic microsatellite loci were characterized, and 12 of them were selected to genotype individuals from two populations. Microsatellite amplifi cation was conducted in two multiplex groups, each containing six microsatellite loci. Cross-species amplifi cation was tested in seven other species of Sebaea . The 12 novel microsatellite loci amplifi ed only in the two most closely related species to S. aurea (i.e., S. ambigua and S. minutifl ora ) and were also polymorphic in these two species. • Conclusions: These results demonstrate the usefulness of this set of newly developed microsatellite loci to investigate the mating system and population genetic structure in S. aurea and related species.
Variation and evolution of herkogamy in Exochaenium (Gentianaceae): implications for the evolution of distyly
Taxonomy of Exochaenium and Lagenias: two resurrected genera of tribe Exaceae (Gentianaceae)
Diplostigmaty in plants: a novel mechanism that provide reproductive assurance
Differentiation of female sexual organs in flowering plants is rare and contrasts with the wide range of male reproductive strategies. An unusual example involves diplostigmaty, the possession of spatially and temporally distinct stigmas in Sebaea (Gentianaceae). Here, the single pistil within a flower has an apical stigma, as occurs in most flowering plants, but also a secondary stigma that occurs midway down the style, which is physically discrete and receptive several days after the apical stigma. We examined the function of diplostigmaty in Sebaea aurea, an insect-pollinated species of the Western Cape of South Africa. Floral manipulations and measurements of fertility and mating patterns provided evidence that basal stigmas function to enable autonomous delayed self-pollination, without limiting opportunities for outcrossing and thus avoiding the costs of seed discounting. We suggest that delayed selfing serves as a mechanism of reproductive assurance in populations with low plant density. The possession of dimorphic stigma function provides a novel example of a flexible mixed-mating strategy in plants that is responsive to changing demographic conditions.