Karyomorphology of three Halophila species (Hydrocharitaceae, Alismatales) from Haad Chao Mai National Park, Trang Province, Thailand

Abstract

The taxonomic identification of some species of Halophila, a marine angiosperm genus in the Hydrocharitaceae family, remains complicated by morphological plasticity. Therefore, the karyotypes were determined for three Halophila species from Haad Chao Mai National Park, Thailand: H. beccarii, H. major and H. ovalis. The results showed that the chromosome numbers of all the studied Halophila were 2n = 18. However, there were inter-specific differences in the karyotype formulae. The karyotype formulae of H. beccarii, H. major and H. ovalis (2n = 6m + 4sm + 8st, 2n = 8m + 6sm + 4st, and 2n = 8m + 4sm + 6st, respectively) were distinctly different from those found in previous studies of specimens from Hong Kong, China and India. This indicates biogeographically karyotypic variation among populations. This is the first report of karyotypes of three Halophila species from Thailand. Several karyotype asymmetry indices were also examined. According to karyotype asymmetry index (A), Halophila beccari had the most asymmetrical karyotype (A = 0.33) that agreed with the highest subtelocentric chromosomes. These karyotype features can be applied to further studies, for example, taxonomy, physiology and chromosome evolution.