Preliminary report on the molecular phylogeny of the Laurencia complex (Rhodomelaceae)

A molecular phylogenetic analysis of three closely related red algal genera, Laurencia, Chondrophycus and Osmundea (Rhodomelaceae) that are often called the Laurencia complex or Laurencia sensu lato, mainly of the north-western Pacific species, was carried out based on rbcL gene sequences. The sequence data downloaded from GenBank were also included in our analysis. The monophyly of the clade of Osmundea species was supported by high bootstrap value. All examined species of Laurencia sensu stricto with typical features (four periaxial cells per vegetative axial segment, longitudinally oriented secondary pit-connections between contiguous superficial cortical cells, corps en cerise within superficial cortical and trichoblast cells) also constituted a monophyletic clade with high bootstrap value. On the other hand, Chondrophycus species were divided into two separated clades with relatively high bootstrap values respectively. Furthermore, L. flexilis, which has four periaxial cells per vegetative axial segment but lacks secondary pit-connections between contiguous superficial cortical cells, constituted an independent monophyletic clade with high bootstrap value. These results suggest that only two groups, Osmundea and the typical Laurencia, are monophyletic and Chondrophycus is polyphyletic within the Laurencia complex. The phylogenetic position of L. flexilis, an intermediate species between the typical Laurencia and Chondrophycus, must be clarified to determine the key features to distinguish Chondrophycus and Laurencia sensu stricto. Further investigations based on the other genes are expected