The reinstatement of Plocamium robertiae (Rhodophyta, Plocamiales) and an updated species inventory of the genus in South Africa

The morphologically diverse and widespread red algal genus Plocamium has recently emerged as a source of bioactive compounds with potential application in the pharmaceutical industry. However, species identification and the taxonomy of the group remains problematic. An initial contribution to the taxonomy of Plocamium in South Africa was therefore carried out using combined morphological and molecular approaches and existing literature. Plocamium robertiae is reinstated as a distinct species based on molecular and morphological evidence, while Plocamium raphelisianum, a species from Spain, is placed in synonymy with P. suhrii. Along the South African coast, individuals of P. suhrii were genetically divergent in different bioregions and will require further investigation. Contrary to previous reports, we confirm the absence in South Africa of two Australasian species, P. microcladioides and P. mertensii, which were previosuly misidentified. The latter species likely represents a new, undescribed species in South Africa. Two additional species were also identified based on DNA but require further morphological assessment. We now recognize P. robertiae, along with eight other named species, plus five additional taxa, with varying levels of taxonomic confidence, and exclude P. microcladioides and P. mertensii from the South African flora. This study doubles the number of species recognized since the last biodiversity assessment of Plocamium and expands the distributional range of P. suhrii. Although our findings contribute an initial assessment assisted by DNA data, a full understanding of the taxonomy of Plocamium in South Africa is far from complete.

Automated summary

The taxonomy of the red algal genus Plocamium remains problematic, and a study on this genus in South Africa has identified several species using morphological and molecular approaches. Plocamium robertiae is reinstated as a distinct species, while Plocamium raphelisianum is placed in synonymy with P. suhrii. Additional species were also identified, but further morphological assessment is needed.