EVOLUTIONARY TRENDS IN THE SEAGRASS GENUS HALOPHILA (THOUARS): INSIGHTS FROM MOLECULAR PHYLOGENY

摘要

Relationships among members of the seagrass genus Halophila (Hydrocharitaceae) were investigated using phylogenetic analysis of the internal transcribed spacer (ITS) region of the nuclear ribosomal DNA. The final aligned ITS sequence data set of 705 base pairs from 36 samples in 11 currently recognised species included 18.7% parsimony informative characters. Phylogenetic analysis yielded two most parsimonious trees with strong support for six groups within the genus. Evolutionary trends in Halophila appear to be toward a more reduced simple phyllotaxy. In addition, this study indicates that long distance 'jump' dispersal between major ocean systems may have occurred at least in the globally distributed H. decipiens. Results of ITS analyses also indicate that the widespread pacific species H. ovalis is paraphyletic and may contain cryptic species. Likewise, the geographically restricted species H. hawaiiana and H. johnsonii could not be distinguished from H. ovalis with these data and warrant further investigation.