Morphometric and molecular analyses confirm two distinct species of Calliarthron (Corallinales, Rhodophyta), a genus endemic to the northeast Pacific

Phylogenetic analyses of rbcL sequences demonstrate that Calliarthron as currently constituted is paraphyletic. Calliarthron yessoense and C. latissimum from the northwest Pacific belong in Alatocladia and are conspecific. After the transfer of C. yessoense and C. latissimum, Calliarthron is monophyletic, known only from the northeast Pacific and comprises two species, C. cheilosporioides and C. tuberculosum, which are distinct morphologically, biogeographically and by molecular sequence. Sequence data for the types of C. regenerans and C. setchelliae confirm that they are heterotypic synonyms of C. tuberculosum. Lectotypes are designated for C. cheilosporioides, C. regenerans and C. setchelliae. A morphometric analysis shows that three measured characters reliably distinguish C. cheilosporioides from C. tuberculosum. Alatocladia is monophyletic, known only from the northwest Pacific and comprises two species, A. modesta and A. yessoensis, which are distinct morphologically, biogeographically and by molecular sequence. rbcL sequence data of the type species of Alatocladia, Bossiella, Calliarthron and Chiharaea confidently differentiate these genera with strong bootstrap support.