Abstract
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.
Highlights
Few cytological studies have focused on the tropical plant family Costaceae Nakai
One of the new counts is for an undescribed species of Paracostus
The chromosome counts revealed two somatic numbers among the samples, namely 2n = 18 and 2n = 36; the former is a new number in the genus Paracostus, the only other count available so far being 2n = 36 in P. englerianus (Mahanty, 1970)
Summary
Few cytological studies have focused on the tropical plant family Costaceae Nakai. The majority of chromosome numbers obtained are of Neotropical members of the family, which show a predominant somatic number of 2n = 18 (Mahanty, 1970; Maas, 1972), and only four Asian species of the family have been counted (Table 1).
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