Expanding Fluvioralfsiaceae diversity: Deniella gen. nov., with two new marine crustose brown algae (Ralfsiales, Phaeophyceae) from the Eastern Pacific

The order Ralfsiales primarily comprises crustose brown algae distributed globally in temperate and tropical seas. Although ecologically significant, their taxonomic identification is often complicated by morphological similarity among genera and species. In this study, we describe a new genus, Deniella gen. nov. within the family Fluvioralfsiaceae, based on combined morphological and molecular evidence. Phylogenetic analyses using rbcL and COI-5P sequences support the monophyly of Deniella and its placement as a distinct lineage within Fluvioralfsiaceae, clearly separated from the freshwater genus Fluvioralfsia and other undescribed taxa within the family. Deniella is characterized by thick, coriaceous, nonoverlapping thalli, with predominantly unilateral symmetry, a well-developed and clearly differentiated medulla and cortex, a single chloroplast per cell and intercalary unangia developed from the basal cells of paraphyses. The two new species, D. nahuae sp. nov. and D. aymarae sp. nov. from the tropical Pacific coast of Mexico and the temperate northern coast of Chile, respectively, differ in thallus thickness, cell dimensions of the medulla and cortex, whether reproductive sori are visible in surface view and the developmental pattern of plurangial sori. The occurrence of intercalary unangia in Deniella, together with similar observations in other ralfsialean taxa, supports the emendation of the diagnostic circumscription of the order to encompass both terminal and intercalary unangial development.