NEW CHROMOSOME COUNTS OF ASIAN COSTACEAE AND INITIAL INSIGHTS INTO THE GENOME EVOLUTION OF THE FAMILY

Chromosome counts were obtained from six species of Costaceae from Asia. Our count of 2n = 18 for Cheilocostus speciosus confirms previous counts, and the other five counts have been made for the first time (Cheilocostus borneensis, Cheilocostus globosus, Cheilocostus sopuensis, Costus muluensis and Paracostus sp.). These chromosome counts reveal two somatic numbers, 2n = 18 and 2n = 36, of which the former is a new diploid number for the genus Paracostus. A comprehensive review of existing counts was conducted through literature and database searches. Mapping of these on a published comprehensive phylogenetic tree suggests that the diploid count of 2n = 18 is probably ancestral in the Costaceae, with repeated parallel evolution of tetraploidy and one case of octoploidy. The existence of triploid counts in several lineages harbouring polyploids suggests that diploids and tetraploids may exist in close proximity, and that crosses or meioticirregularities may lead to triploid genotypes occurring frequently.