Phylogeny of Betaphycus (Gigartinales,Rhodophyta) as inferred from COI sequences and morphological observations on B. philippinensis

The phylogeny of the three species that comprise the genus Betaphycus Doty in Silva, Basson and Moe and their phylogenetic relationships with other eucheumatoids are still unresolved. In this study, the utility of the mitochondrial cytochrome oxidase I (COI) marker in resolving their relationships was evaluated. Analyses of the COI sequences from Betaphycus philippinensis Doty and Betaphycus speciosus (Sonder) Doty ex Silva specimens collected from their type localities (Sorsogon, Philippines and Western Australia, respectively) revealed that the two species formed a well-supported clade distinct from Eucheuma J. Agardh and Kappaphycus Doty ex Silva. The genotyped specimens of B. philippinensis were observed to exhibit dorsal protuberances, a characteristic which has been regarded as a key diagnostic feature of Betaphycus gelatinus (Esper) Doty ex Silva. This observation raised the possibility that these two taxa are conspecific. In addition, B. philippinensis specimens were also observed to exhibit morphological features that could be used to distinguish the species from other eucheumatoids, such as the location tetrasporangial nemathecium in the thallus and the presence of apical or lateral pit connections in the tetraspores. The species referred to in the literature as “B. gelatinus” (as Eucheuma gelatinae) collected from northwestern Philippines was identified as a species of Eucheuma based on molecular and morphological evidence. The phylogenetic relationships of this species with other related eucheumatoid taxa were also determined.