Genetic variation, clonal diversity and breeding system in sedges (Carex)

Abstract: In this thesis I investigate genetic variation in clonal plants within the wind-pollinated plant family Cyperaceae and, in particular, in species of Carex. Clonal diversity and the spatial distribution of clones (genets) within populations was investigated in Carex bigelowii (in Iceland and Scandinavia) and C. arenaria (within the species' entire distributional range in W Europe). Both species reproduce mainly by vegetative growth, via rhizomes with long internodes between shoots, and seedling recruitment in established populations is extremely rare or absent. The C. bigelowii populations show high levels of clonal diversity but Ð contrary to predictions based on the extensive clone structure Ð little interdigitation of genets within local patches. Carex arenaria populations are generally multiclonal, but there appear to be some monoclonal populations in SW Europe. A literature survey of of allozyme data in species of Cyperaceae revealed a strong correlation between clonal growth form and plant breeding system. While caespitose species are generally inbreeding and show little within-population variation, rhizomatous species are outcrossing and have high levels of within population variation. Allozyme investigations of the rhizomatous sedges Carex arenaria, C. bigelowii, C. caryophyllea and C. ericetorum, suggest that these four species are all outbreeders. Carex arenaria, has, however, unusually low overall levels of genetic variation for a rhizomatous sedge. This lack of variation was interpreted in terms of the species' history of glacial survival and postglacial spread. The species-pair C. caryophyllea and C. ericetorum was investigated for ecological amplitude and niche separation in mixed populations in Alvar grassland communities. The two species showed an almost complete overlap in habitat niche, but had partially separate flowering periods. There was a phenological window for pollen transfer from C. caryophyllea to C. ericetorum and allozyme data suggest that there may be gene flow from C. caryophyllea to C. ericetorum.