Type‐assisted taxonomy and biogeography of Corallina (Corallinales, Rhodophyta) in the eastern Pacific: Corallina americana sp. nov., C. bathybentha, C. hommersandiorum sp. nov., and C. saundersii sp. nov

The articulated coralline genus Corallina is common in temperate rocky ecosystems and provides settlement substrate and refugia for other organisms. However, our ability to understand species-specific traits and interactions has been confounded by overlapping morphological characteristics among species. DNA sequences from type specimens and recently collected specimens have begun to address these issues by clarifying phylogenetic species boundaries and geographic distributions. We sequenced an rbcL gene barcode from a paratype specimen of Corallina bathybentha (type locality: 0.5 miles south of the west end of Anacapa Is., California, United States) and have provided an updated description. Three cryptic species have been described: C. hommersandiorum and C. saundersii are endemic to the northeastern Pacific, whereas C. americana is anti-tropical in the eastern Pacific. Haplotype network analyses using the COI locus suggested that C. americana naturally dispersed from North to South America; it was not likely a recent or human-mediated introduction. To explore species boundaries, stepwise discriminant models were used to analyze morphological and ecological traits and were visualized in canonical multidimensional plots. Every species overlapped in canonical space with at least one other species, further illustrating that morphological identifications of Corallina species are challenging and unreliable. This work completes the taxonomic study of the currently known diversity of Corallina in the northeast Pacific for which we have access to type specimens. Given that this region is likely the center of origin and home to three-quarters of the known Corallina species, these taxonomic studies, including this one, make a significant contribution to our understanding of coralline diversity.