Ceramothamnion codii, GENETIC

Maggs, Maria Beatriz Barros-Barreto Jeffery R. Hughey Christine A., 2025, Genome sequencing of Phycotheca Boreali-Americana material of Ceramothamnion codii H. Richards confirms synonymy of Stirkia Barros-Barreto & Maggs with Ceramothamnion H. Richards, Cryptogamie, Algologie 20 (7), pp. 89-113 : 94-96

CERAMOTHAMNION CODII GENETIC ANALYSIS

The rbc L gene is the most commonly used marker within the Ceramiales ( Cassano et al. 2019; Díaz-Tapia & Verbruggen 2024), therefore obtaining an rbc L sequence from authentic material of Ceramothamnion codii made it possible to phylogenetically confirm the circumscription of Ceramothamnion . High-throughput sequencing of red algal type and other historically valuable herbarium specimens has been shown to be useful for resolving many systematic questions in the red algae ( Hughey et al. 2014, Boo et al. 2016, Gabrielson et al. 2018, Hughey & Miller 2021, Hughey et al. 2022). Although whole genome sequencing here was unable to decipher the complete organellar genomes as reported by the studies above, this analysis successfully generated a sufficient number of reads to assemble the standard phylogenetic genetic markers required to conclusively characterize the generic affinity of the 112 year-old topotype C. codii specimen from Bermuda. Although low standard bootstrap supports were observed for the rbc L , LSU and combined datasets, all three analyses positioned Ceramothamnion species together in a single clade. In addition, these analyses show that C. codii is placed in the same clade as the generitype of Stirkia , S. fujiiana , and therefore support the transfer of all Stirkia spp. to Ceramothamnion as proposed by Wynne & Schneider (2023). Seo et al. (2023) resolved a fully supported Ceramothamnion clade in their maximum likelihood phylogeny of the Ceramiales based on nucleotide sequences of 23 protein-coding genes. In addition, our results indicate that the two publicly available sequences in GenBank from Hawai‘i deposited under the name Ceramium codii (collection number ARS03339, LSU and 23S plastid gene sequences) do not represent the same species as the type material from Bermuda. The genetic distances exhibited between the Hawai‘i and Bermuda specimens are higher than

FIG. 6. — Reconstructed phylogeny of the red algal tribe Ceramieae C.Agardh ex Greville based on concatenated rbc L , LSU and COI-5P gene sequences. Majority rule consensus tree resulting from Bayesian analysis. Values at the nodes represent posterior probability and bootstrap values for ML, support lower than 0.90 (PP), 80 (Ultrafast Bootstrap) and 50 (BP) are not shown. *, full support. Sequences generated in this study are in bold and the topotype sequence is underlined. Abbreviation: UKOTs, United Kingdom Overseas Territories, United States.

typically observed in intraspecific pairwise comparisons. The Hawai‘ian specimen thus appears to represent an undescribed species of Ceramothamnion .

Three isotype specimens of Ceramothamnion codii P.B.-A. no. 845 are housed in the New York Botanical Garden Herbarium under numbers NY2348656, NY02116304, and NY02116306. Specimen NY2348656 contains a slide with filaments on it and an approximately 2.0 cm excised fragment of Codium with a scant amount of visible dark red Ceramothamnion filaments. This small Codium fragment is mounted on its own paper and has been removed with a razor blade and placed in an envelope on the herbarium sheet. The second specimen, NY02116304, also contains a slide with tufts on it (labeled 845a) and three small 0.5-1.0 cm sized Codium fragments with some visible Ceramothamnion filaments. This specimen too has been removed with a razor blade and placed in an envelope. The third specimen NY02116306, was selected as the lectotype of Ceramothamnion codii because it includes nine full-sized Codium thalli, all with numerous and conspicuous pinkish red C. codii filaments covering the fronds. In addition, the original drawings from the Algae of Bermuda ( Collins & Hervey 1917) are mounted adjacent to the envelope containing the nine specimens. Ceramothamnion codii no. 1899 is topotype material distributed in the P.B.-A., molecularly characterized here in this paper.