A morphological and molecular study of austral sargassum (fucales, phaeophyceae) supports the recognition of Phyllotricha at genus level, with further additions to the genus sargassopsis

Abstract

Sargassum subgenus Phyllotricha currently includes seven species restricted to Australian and New Zealand coasts. A recent study of Cystoseira and other Sargassaceae genera based on mitochondrial 23S DNA and chloroplast-encoded psbA sequences resulted in the most widely distributed species of subgenus Phyllotricha, Sargassum decurrens, being transferred to the reinstated monospecific Sargassopsis Trevisan. The fate of the residual six Phyllotricha species, however, was not considered. The present study examines these Phyllotricha species, alongside other Sargassum subgenera, Sargassopsis, Sirophysalis trinodis (formerly Cystoseira trinodis) and the New Zealand endemic Carpophyllum Greville, using morphological evidence and the molecular phylogenetic markers cox3, ITS-2 and the rbcL–S spacer. Our results suggest both the genus Sargassum and Sargassum subgenus Phyllotricha are polyphyletic as currently circumscribed. Four S. subgen. Phyllotricha species, i.e. S. sonderi, S. decipiens, S. varians and S. verruculosum, form a monophyletic group sister to the genus Carpophyllum, and S. peronii is genetically identical to S. decurrens with regard to all three loci. We propose the resurrection of the genus Phyllotricha Areschoug, with type species Phyllotricha sonderi, and include the new combinations Phyllotricha decipiens, Phyllotricha varians and Phyllotricha verruculosum. Sargassum peronii, S. heteromorphum and S. kendrickii are transferred to Sargassopsis and Sargassum peronii is considered a synonym of Sargassopsis decurrens.