Fletcheria gen. nov. (Ralfsiales, Phaeophyceae): A new crustose brown algal genus clarifying evolutionary relationships of Ralfsia pacifica

The genus Ralfsia was historically broadly circumscribed but has recently undergone significant taxonomic revision. Based on molecular data, a restricted Ralfsia sensu stricto was delineated that had many species reassigned to new genera and families. The current work builds on that work by resolving the phylogenetic position, defining the morphological features, and establishing the biogeographic distribution of Ralfsia pacifica-a crustose brown alga widely distributed along the eastern Pacific coastline. We employed mitochondrial COI-5P and plastid rbcL gene markers, together with morpho-anatomical observations and comparisons with type material, to better understand this species and its distribution. Phylogenetic analyses positioned R. pacifica as a distinct lineage, sister to Neoralfsia within Neoralfsiaceae with moderate support. Significant molecular divergence from its nearest neighbor combined with a unique suite of morphological features-crustose thallus lacking clear differentiation of the cortex and medulla, frequent hair pits, and slightly elevated but largely nonadventitious plurangial sori-supported the establishment of Fletcheria gen. nov., with Fletcheria pacifica comb. nov. as the generitype, provisionally assigned to Neoralfsiaceae. The species was confirmed from British Columbia, Canada; California, United States; and central Chile, occupying intertidal habitats and reproducing year round with seasonal peaks. Based on morpho-anatomical observations, Ralfsia occidentalis is excluded from synonymy with F. pacifica. Anatomical features, although limited, place it closer to the genus Neoralfsia.