TAXONOMIC REVISION AND GEOGRAPHIC DISTRIBUTION OF THE SUBGENUS SARGASSUM (FUCALES, PHAEOPHYCEAE) IN THE WESTERN AND CENTRAL PACIFIC ISLANDS BASED ON MORPHOLOGICAL AND MOLECULAR ANALYSES(1).

Abstract

The species diversity of the subgenus Sargassum was reassessed for the southwestern Pacific with special focus on the Solomon Islands, Vanuatu, Fiji, and Wallis. Five taxa were recognized on the basis of morphological characters and corroborated by DNA analyses of the nuclear internal transcribed spacer 2 (ITS-2), chloroplastic partial rbcLS-operon, and mitochondrial cox3. Based on the study of diagnoses and type specimens, four taxa were identified to S. polyphyllum J. Agardh, S. polycystum C. Agardh, S. aquifolium (Turner) C. Agardh, and S. ilicifolium (Turner) C. Agardh, while one taxon remained unidentified. We present a key for identification that includes detailed descriptions of the species and illustrations of their morphological variability. In light of our findings, we propose to consider several new synonymies for S. aquifolium, S. ilicifolium, S. polycystum, and S. polyphyllum. We also include a review of Sargassum floras from Samoa, Tonga, and Nauru and discuss species distribution in the southwest and central Pacific. Finally, DNA phylogenies pointed to the polyphyly of section Acanthocarpicae and underlined the need for a new section in which to place S. polycystum, S. herporhizum Setch. et N. L. Gardner, and S. stolonifolium Phang et T. Yoshida. The new section Polycystae Mattio et Payri is described to fit species of the subgenus Sargassum with stolon-like branches.