Codium, Stackhouse, 1797

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 : 96-97

CODIUM GENETIC ANALYSIS

It was surprising to find Codium fragile (Suringar) Hariot chloroplast DNA sequences amongst the Codium decorticatum genome reads from the two host plants on NHM sheet no. 1899. We are uncertain which thalli represent which species because the two fragments were combined into a single tube for the DNA extraction to maximize the number of Ceramothamnion codii sequences obtained from the WGS. What is further perplexing is that no sequences of Codium fragile from Bermuda are publicly available in GenBank, nor has the name been reported from Bermuda ( Schneider 2003; Guiry & Guiry 2024). It is possible that the Codium fragile from the topotype sheet of Ceramothamnion codii represents the invasive strain of the species, Codium fragile subsp. tomentosoides (van Goor) P.C.Silva , because the partial rpl16-rps3 sequence we obtained excludes atlanticum subsp. (Cotton) P.C.Silva and the following haplotypes: Northeast Pacific, South Africa, New Zealand, Tasmania and Mexico as defined by Provan et al. (2008). The two haplotypes/subspecies that cannot be excluded based on the mutations recovered from the genomic data are subsp. tomentosoides and the China haplotype.

In summary, HTS of archival 1912 topotype material of C. codii generated an adequate number of endogenous reads to assemble standard genetic markers and thereby corroborate the taxonomic placement of C. codii in the genus Stirkia . The data was also able to confirm two host plant species, Codium fragile and Codium decorticatum .