Genome sequencing of Phycotheca Boreali-Americana material of Ceramothamnion codii H.Richards confirms synonymy of Stirkia Barros-Barreto & Maggs with Ceramothamnion H.Richards

The systematic status of the newly proposed genus Stirkia Barros-Barreto & Maggs and its relationship to the currently accepted name Ceramothamnion H.Richards remain uncertain because no authentic specimens of the generitype C. codii H.Richards from the type locality in Bermuda have been sequenced. To clarify the taxonomy of C. codii, we performed high-throughput sequencing on a topotype, a 1912 Phycotheca Boreali-Americana (P.B.-A.) specimen collected by F.S. Collins. The rbcL, COI-5P and LSU genetic markers from the P.B.-A. specimen were assembled and used to infer gene and multi-gene phylogenies to determine its phylogenetic history. In all analyses, the topotype of C. codii was closely allied with C. fujianum Barros-Barreto & Maggs, the generitype of Stirkia, as well as with other species of Ceramothamnion from the southwestern Atlantic and Pacific Oceans. These data support the relegation of the genus Stirkia to Ceramothamnion and indicate that the only previously published DNA sequences of C. codii, from Hawai‘i, represent a different, presumably undescribed species of Ceramothamnion. They also highlight the power of whole genome sequencing and the need to analyse type, topotype, or historically authentic herbarium specimens to ensure the accurate application of algal binomials.