Experimental Hybridizations Among Chromosome Races of Carex pachystachya and the Related Species C. macloviana and C. preslii (Cyperaceae)

Abstract

Artificial hybridizations and compatibility studies were conducted on four chromo- some races of Carex pachystachya and two related species, C. macloviana and C. preslii. As measured by percent seed set, percent seed germination, and percent germination as a function of the total number of flowers, three levels of compatibility were found. The highest level was obtained through selfing, indicating the plants are self compatible and likely to be autogamous in nature. Lower compatibility was observed when plants were outcrossed. The lowest level of compatibility was obtained in interracial and interspecific crosses, although seed set and germination values as high as 79% and 100%, respectively, indicate plants are cross compatible, with crosses among species as successful as among races. No conclusive evidence of agamospermy is found. As in other Carex groups, ecogeographic factors and breeding system are primarily involved in maintaining repro- ductive isolation among the species. Considering the results in the context of agmatoploid evolution indicates that changes in chromosome number have little to no effect on compatibility among closely related species, and thus chromosome number changes at most may be only associated with genetic adaptations to new habitats.