What is Corallina officinalis var. chilensis? An examination of nomenclature, biogeography, phylogeny, and morphology

Geniculate coralline algae are notoriously challenging to identify in the field due to confusing morphological variation. Consequently, former species delimitations based exclusively on morphology are often unsupported by sequence-based phylogenies. The purpose of my research was to determine whether Corallina chilensis Decaisne, basonym of C. officinalis var. chilensis, was a distinct species or should be considered a variety of C. officinalis; and consequently whether C. chilensis was distributed in two hemispheres. In order to answer these questions, I sequenced psbA, CO1, and rbcL genes from 76 voucher specimens representing Corallina collections from ~2000 to 2019. I applied names by comparing these sequences with published sequences and type specimen sequences, including an rbcL sequence from the specimen collected by Darwin (#2151 from Valparaiso, Chile), the holotype specimen for C. chilensis designated by Harvey. I used phylogeny with additional support from morphometric, Automatic Barcode Gap Discovery, and distance matrix analyses for species delimitation. DNA from the Chilean C. chilensis holotype matched an unnamed coralline species commonly found in the Northeast Pacific, and C. chilensis specimens formed a separate clade from C. officinalis specimens in my phylogenetic analyses. Corallina chilensis is a distinct species, not a variety of C. officinalis, and it is present in both hemispheres. Going forward, the name C. officinalis var. chilensis should be discontinued, and the older name C. chilensis should be used in its place.Science, Faculty ofBotany, Department ofGraduat