Genetic variability and biogeography of the widespread red alga Hypnea flexicaulis (Gigartinales, Rhodophyta) based on rbcL and cox1 sequences

Hypnea flexicaulis is a carrageenophyte red alga that commonly occurs on various substrata in the lower intertidal of the Indo-Pacific Ocean. To examine the genetic variability within the species and the relationships of genetic lineages to contemporary distribution, we analyzed plastid rbcL and mitochondrial cox1 genes from specimens collected in eight countries. Phylogenetic trees of rbcL revealed a monophyly of H. flexicaulis. In the cox1 tree, H. flexicaulis comprised four genetic groups: one group was dispersed throughout the Indo-Pacific region, and the remaining three lineages were geographically localized to Australia, India, and the Philippines. Thus, the contemporary distribution of H. flexicaulis may result from a mixture of modern current flows, anthropogenic agents, and historical dispersal events.