Phylogenetic Relationships of Sargassum subgenus Bactrophycus (Sargassaceae, Phaeophyceae) inferred from rDNA ITS Sequences

doi:2002.17.4.235

Algae > Volume 17(4); 2002 > Article

Algae 2002;17(4): 235-247. doi: https://doi.org/10.4490/ALGAE.2002.17.4.235

Jung hyun Oak, Youngbae Suh, In Kyu Lee

School of Biological Sciences, Seoul National University, Natural Products Research Institute, Seoul National University

ABSTRACT

Phylogenetic relationships of Sargassum with the emphasis on subgenus Bactrophycus were examined on the basis of internal transcribed spacer (ITS) and 5.8S sequences of nuclear ribosomal DNA (rDNA) for 23 accessions of Sargassum representing 18 species, and two outgroups, Hizikia fusiformis (harvey) Okamura and Myagropsis myagroides (Mertens ex Turner) Fensholt. Fifteen species were included in the molecular analysis to represent all sections of the subgenus Bactrophycus recognized to dat (Spongocarpus, Teretia, Halochloa, and Repentia), and additional three species were analyzed to represent three other subgenera of Sargassum (Sargassum, Schizophycus, and Phyllotrichia) found in Korea. In the resulting phylogenetic trees, H. fusiformis was nested in the clade of subgenus Bactrophycus as sister group of section Teretia with high confidence even though it was designated as one of outgroups in the phylogenetic analysis. Species of section Teretia formed a very robust clade. Section Spongocarpus was branched off as a sister group of the Hizikia-Teretia clade. Members of section Halochloa showed very little differences in ITS sequences and formed a very tight clade with S. yezoense, which is a member of section Repentia (99% in bootstrap analysis). Sequences of ITS of S. yezoense was identical with ones of S. siliquastrum, although they belong to different sections, Repentia and Halochloa, respectively. In the phylogenetic analyses of ITS sequences, members of subgenus Bactrophycus including the monotypic genus Hizikia were clearly separated from other subgenera of Sargassum as forming a highly supported monoophyletic group. The molecular data strongly claim that Hizikia should be treated as a member of the genus Sargassum. The molecular study also suggests that sections Repentia and Halochloa are closely allied, but further analyses with more extensive sampling should be needed to look into taxonomic circum criptions for sections Halochloa and Repentia, of which taxonomic limitations were not clearly defined in this study.

Key words: Hizikia, ITS, phylogeny, rDNA, Sargassum subgenus Bactrophycus, sequences