Multi-gene phylogeny reveals a new genus and species of Hapalidiales (Rhodophyta) from Antarctica: Thalassolithon adeliense  gen. et sp. nov.
Over the last decade, the genetic diversity of coralline red algae has been gradually unraveled using DNA sequence data. This resulted in the discovery of many novel lineages and taxonomic reassessments at genus and species level. Despite this, our knowledge of the diversity of these organisms in some inaccessible regions of the planet, such as Antarctica, remains incomplete. In this study we re-examined collections of a crustose coralline of uncertain taxonomic identity made in 2013, during the XXVIII Italian Expedition in Antarctica (from Adélie Cove, Terra Nova Bay). This alga was characterized through a polyphasic approach combining DNA sequence data obtained for four genes (psbA, rbcL, 18S rRNA and cox1) with morpho-anatomical analyses and analyses of elemental composition of different parts of the thallus. Molecular phylogenetic reconstructions unambiguously recovered this alga as a member of the order Hapalidiales, but without any close relationship with any well-established genus of this order. Instead, it formed a well-supported lineage with specimens named Hapalidiales sp. ZH-Twist-2019, collected in New Zealand, for which no formal assignment at genus level has been proposed yet. Species delimitation methods (ABGD, PTP, GMYC) applied to the psbA dataset indicate that our Adélie Cove coralline is a distinct species from all other known hapalidialean species. Based on our results, here we describe this lineage as the new genus Thalassolithon Trentin, Moschin & Moro, and our alga as Thalassolithon adeliense Trentin, Moschin & Moro.