Corallina(Corallinales, Rhodophyta) from Tristan da Cunha and the Falkland Islands: implications for South Atlantic biogeography

A molecular and morphological taxonomic study ofCorallina(Corallinales, Rhodophyta) from Tristan da Cunha and the Falkland Islands revealedCorallina chamberlainiaeJ.Brodie & R.Mrowicki sp. nov. from both South Atlantic archipelagos, andCorallinacf.caespitosaonly in the Falkland Islands. Analysis of mitochondrial COI-5P and plastidpsbA resolvedC. chamberlainiaeas a distinct clade composed of specimens from Tristan and the Falkland Islands (COI-5P), in addition to two matching New Zealand samples (psbA). InpsbA analyses,C. cf.caespitosawas close to two species from Japan (asC. piluliferaandC. melobesioides) but was separate fromC. caespitosasensu stricto from Britain andC. ferreyrae(isotype) from Peru. In COI-5P analyses,C. cf.caespitosawas in a clade withC. caespitosa(holotype) and close to, but distinct from,C. ferreyraeand an unidentified South AfricanCorallinaspecies. Application of the Automatic Barcode Gap Discovery (ABGD) and Poisson tree processes (bPTP) for COI-5P lumpedC. chamberlainiaeinto one clade, whereas the Generalized Mixed Yule Coalescent (GMYC) model split it into two well-supported groups, one of which only contained Falkland Island specimens. All three models lumpedC. cf.caespitosawithC. caespitosa. C. chamberlainiaeclosely resemblesC. officinalis, the generitype, but is distinguished by smaller size and a more compressed thallus towards the apex.Corallinacf.caespitosaresemblesC. caespitosabut is smaller and has fused, palm-like upper fronds. Neither of these taxa is conspecific withC. ferreyraealthoughC. caespitosawas recently synonymized withC. ferreyrae. C. chamberlainiaeandC. cf.caespitosaoccupy similar intertidal habitats to their respective, closely related counterpartsC. officinalisandC. caespitosa. The results indicate cryptic diversity and suggest that there are many misidentifiedCorallinaspecies. The paucity of South Atlantic studies of the Corallinales points to the need for a much greater taxonomic effort in this biogeographic region.