Phylogenetic analysis of invasive genus Lophocladia (Rhodomelaceae, Rhodophyta) reveals synonymy of L. lallemandii with L. trichoclados and first record of L. kuetzingii in the NE Atlantic

Species identification in red algae poses significant challenges when relying solely on morphological characteristics. Consequently, the absence of molecular information often conceals misidentifications, cryptic diversity and introduced cryptic species. Within the genus Lophocladia, species have traditionally been delineated based on subtle morphological traits. Lophocladia trichoclados and Lophocladia lallemandii have been extensively documented in warm and temperate coastal regions, with the latter recognized as an invasive species in the Mediterranean. However, the molecular relationship between these species remains unexplored. To address this gap, a comprehensive taxonomic reevaluation of Lophocladia was conducted in the NE Atlantic, Mediterranean Sea and Red Sea. Through combined molecular and morphological analyses of 75 specimens, two distinct taxa of Lophocladia were identified within the study area. Sequences of the rbcL plastid gene unequivocally demonstrated that L. lallemandii and L. trichoclados are conspecific. Consequently, we propose the synonymization of L. lallemandii with L. trichoclados, which has nomenclatural priority. We report L. kuetzingii, a potentially introduced species from Australia, for the first time in the Macaronesian region of the North Atlantic. This finding underscores the importance of expanding red algal DNA datasets, as such efforts significantly enhance our ability to detect and discern introduced species. Additionally, this research highlights the existence of taxonomic uncertainties surrounding introduced species, even among those already classified as invasive.