Molecular analyses of turf algae reveal a new species and an undetected introduction in the Pterosiphonieae (Rhodomelaceae, Rhodophyta).

Introduced seaweeds and undescribed species often remain undetected because marine regional floras are as yet poorly understood. DNA sequencing facilitates their detection, but databases are incomplete, so their improvement will continue to lead the discovery of these species. Here we aim to clarify the taxonomy of two turf-forming red algal Australian species that morphologically resemble the European Aphanocladia stichidiosa. We also aim to elucidate whether either of these species could have been introduced in Europe or Australia. We studied their morphology, analysed 17 rbcL sequences of European and Australian specimens, examined their generic assignment using a phylogeny based on 24 plastid genomes, and investigated their biogeography using a taxon-rich phylogeny including 52 rbcL sequences of species in the Pterosiphonieae. The rbcL sequences of one of the Australian species were identical to A. stichidiosa from Europe, considerably expanding its known distribution. Unexpectedly, our phylogenetic analyses resolved this species in the Lophurella clade rather than in Aphanocladia and the new combination L. stichidiosa is proposed. The other Australian species is described as L. pseudocorticata sp. nov. Although L. stichidiosa was originally described in the Mediterranean ca.70 years ago, our phylogenetic analyses placed it in a lineage restricted to the southern hemisphere, showing that it is native to Australia and introduced to Europe. This study confirms that further work using molecular tools is needed to characterize seaweed diversity, especially among the poorly explored algal turfs, and showcases the usefulness of phylogenetic approaches to uncover introduced species and to determine their native ranges.