Reassessment of the diversity of the brown algal genus Colpomenia (Endlicher) Derbès & Solier (Scytosiphonaceae, Ectocarpales) in Argentina based on mitochondrial cox3 gene, including the description of Colpomenia patagonica sp. nov.

Recent molecular phylogenetic studies of members of the brown algal family Scytosiphonaceae Ardissone & Strafforello collected on the coast of Argentina revealed taxonomic misidentifications and hidden biodiversity, resulting in new additions to the seaweed flora of the southwestern Atlantic Ocean. In this work, we reassessed the taxonomy of the scytosiphonacean genus Colpomenia (Endlicher) Derbès & Solier from Patagonian Argentina by integrating mitochondrial cox3 gene information with morpho-anatomical observations. We show here that specimens from Argentina were recovered in two major clades assigned to Colpomenia peregrina Sauvageau and Colpomenia claytoniae S.M.Boo et al., constituting the first report of these species in the southwestern Atlantic Ocean. Within the large C. claytoniae clade, specimens were recovered in two distinct lineages with sequence divergences of 2.72-4.09%, suggesting the occurrence of cryptic diversity. One of these lineages (Lineage 1) has Indo-Pacific Ocean distribution and includes the type specimen of C. claytoniae from South Korea, while the other lineage (Lineage 2) has Atlantic-Pacific Ocean distribution. The Argentinian representatives of Lineage 2 had a saccate and convoluted thallus up to 6.5 cm, four layers of medullary cells, extensive and confluent plurangial sori formed by plurangia and uni or bicellular paraphyses. Considering these, we here describe the new species Colpomenia patagonica M.E. Croce & Santiañez, sp. nov. Our work added three Colpomenia species to the known marine benthic flora of Argentina, increased the number of seaweeds reported in Patagonia, and contributed new knowledge on the diversity and distribution of species in the Scytosiphonaceae.