Cytological studies on Primulina taxa (Gesneriaceae) from limestone karsts in Guangxi province, China

Primulina, a large genus restricted mainly to limestone karst areas, was chosen as a suitable subject for the study of speciation patterns in its center of diversity and endemism at the chromosomal level. We investigated the chromosome numbers and chromosome morphology for 39 species, three varieties and 11 undescribed taxa of Primulina collected from limestone karsts in Guangxi province, China, half of which are known so far to be endemics. The chromosome numbers for the taxa examined were found to be highly constant, all being diploid with 2n = 36. The previously reported basic chromosome number x = 18 was confirmed, as were eight counts; the counts for the remaining taxa reported for the first time except for one gave different numbers from previously published counts. The chromosomes in Primulina are relatively small in size and slight variation occurs among taxa. One or two satellites were encountered in 18 taxa. The relative uniformity in chromosome numbers indicates that variation at the diploid level seems to be the principal feature of chromosomal evolution in this genus and it seems that polyploidization has played a minor role in the diversification and speciation of genus Primulina in limestone areas of SW China.