Molecular analyses resolve the phylogenetic position of Polysiphonia adamsiae (Rhodomelaceae, Rhodophyta) and reveal a strong phylogeographic structure in Australia

Polysiphonia adamsiae was originally described from Tasmania and simultaneously reported in New Zealand. It has an unusual combination of morphological characters: 10-12 pericentral cells and rhizoids in open connection with the pericentral cells. Rhizoid anatomy is similar to that of the tribe Polysiphonieae. However, P. adamsiae differs from most members of the Polysiphonieae in having more than four pericentral cells, a character more common in the tribe Streblocladieae, which is characterised by having rhizoids cut off from pericentral cells. Because this species has not been investigated using molecular methods, it has not been clear to which tribe it belongs. We analysed phylogenetic relationships of P. adamsiae using rbcL sequences from plants collected in Tasmania and Croajingolong National Park (eastern Victoria). The phylogenetic analysis placed P. adamsiae in the Polysiphonieae. Our study further confirmed rhizoidal anatomy as a diagnostic character distinguishing the Streblocladieae from the Polysiphonieae and demonstrated that pericentral cell number varied in these tribes. While most species in the Polysiphonieae have four pericentral cells, at least six species have evolved morphologies with a higher number. Polysiphonia adamsiae is hereby recorded for the first time in mainland Australia based on molecular and morphological evidence. The five haplotypes observed in our 16 rbcL sequences show that the species has strong phylogeographic structure. The Victorian haplotype is distinctive from those in Tasmania, making it is especially valuable in the conservation of this Australasian endemic species.