A re‐assessment of the infra‐generic classification of the genus C aulerpa ( C aulerpaceae, C hlorophyta) inferred from a time‐calibrated molecular phylogeny

The siphonous green algal family C aulerpaceae includes the monotypic genus C aulerpella and the species‐rich genus C aulerpa . A molecular phylogeny was inferred from chloroplast tuf A and rbc L DNA sequences analyzed together with a five marker dataset of non‐caulerpacean siphonous green algae. Six C aulerpaceae lineages were revealed, but relationships between them remained largely unresolved. A C aulerpella clade representing multiple cryptic species was nested within the genus C aulerpa . Therefore, that genus is subsumed and C aulerpa ambigua Okamura is reinstated. C aulerpa subgenus status is proposed for the six lineages substantiated by morphological characters, viz., three monotypic subgenera C liftonii, H edleyi , and C aulerpella , subgenus A raucarioideae exhibiting stolons covered with scale‐like appendages, subgenus C haroideae characterized by a verticillate branching mode, and subgenus C aulerpa for a clade regarded as the C aulerpa core clade. The latter subgenus is subdivided in two sections, i.e., S edoideae for species with pyrenoids and a species‐rich section C aulerpa . A single section with the same name is proposed for each of the other five subgenera. In addition, species status is proposed for C aulerpa filicoides var. andamanensis (W.R. Taylor). All C aulerpa species without sequence data were examined (or data were taken from species descriptions) and classified in the new classification scheme. A temporal framework of C aulerpa diversification is provided by calibrating the phylogeny in geological time. The chronogram suggests that C aulerpa diversified into subgenera and sections after the T riassic‐ J urassic mass extinction and that infra‐section species radiation happened after the C retaceous‐ T ertiary mass extinction.