Abstract
Chromosome numbers for 13 species, including 12 new counts, were reported for Carex distributed in the Ryukyu Islands. Intraspecific aneuploidy (sensu lato) was found in four species and the different types of chromosome number variation pattern within and among populations were recognized in this study. In three species, C. fulvo-rubescens, C. nemostachys and C. sakonis, several intraspecific aneuploid cytotypes were found in the same population. Additionally, notable disturbances of chromosome associations at meiosis were often observed, especially in C. sakonis, and therefore the compatibility among aneuploid cytotypes of these species was readily predictable. In C. sociata, on the other hand, no chromosome number variations within populations and stable chromosome associations at meiosis were found in all investigated populations, and suggesting that these aneuploid cytotypes have differentiated at least to the population level. These two types of variation pattern may indicate that the different aneuploidy mechanisms have operated in Carex population differentiation.
