Ploidy variation in Trigonobalanus verticillata (Fagaceae)

Cytological studies were carried out on two populations of Trigonobalanus verticillata in Yinggeling, Hainan Province, China (YGL), and Fraser's Hill, Malaysia (FH). In the two populations, the pattern of interphase nuclei was of the simple chromocentre type, the mitotic prophases were of the proximal interstitial type and chromosome numbers were 2n = 2x = 14 (YGL) and 2n = 6x = 42 (FH), representing diploid and hexaploid respectively. The basic chromosome number of the species was x = 7; this is a unique number in the Fagaceae and in the Fagales as well. The characteristic karyotype of the diploid population in China was 2n = 14 = 8m + 4sm + 2st. Based on the new finding of the chromosome number in this study, we clarify the previous dispute about the basic chromosome number and propose that the two Asian Trigonobalanus species have closer affinity.