| Summary: | Cryptic species diversity and the misapplication of names have restricted an understanding of species boundaries in the tribe Corallineae of the calcified red algal order Corallinales. Recent DNA sequencing of type material provided a framework facilitating further examination of genera within the tribe. A phylogenetic study of the genera Corallina and Ellisolandia, based on cytochrome c oxidase subunit 1 and ribulose-bisphosphate carboxylase gene sequences, was undertaken using Natural History Museum herbarium collections and contemporary samples to explore species diversity, geographic distributions and the extent to which names have been misapplied. Twenty Corallina clades likely corresponding to species were resolved, of which C. officinalis and C. caespitosa were confirmed, four were clades newly identified during the present study and 14 had been reported by other workers in previous studies. These data indicated considerable genetic diversity within the genus that was not readily apparent on the basis of morphology. The generitype C. officinalis was shown to have a predominantly North Atlantic Ocean, cool-temperate distribution, whereas the global distribution of C. caespitosa is confirmed for the first time, with samples from Asia, Australasia, Europe, Africa and America. Widespread misidentification of Corallina species was documented, as was the need for sequencing of type specimens to correctly apply names and for comparison with historical collections. The phylogeny reported here serves both as a baseline for future phylogenetic positioning of Corallina species and highlights the degree to which species concepts within this genus remain unresolved.
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