Taxonomic revision of Tinocladia (Ectocarpales s.l., Phaeophyceae): merger of Tinocladia with Eudesme and description of E. pseudocrassa sp. nov

ABSTRACT

A molecular phylogeny of Tinocladia and Eudesme based on specimens covering a large proportion of the known species was done using mitochondrial cox1 and cox3, chloroplast atpB, psaA, psbA and rbcL genes and 5.8S rDNA and its ITS2 region sequences. The phylogeny revealed a close phylogenetic relationship between the two genera and the occurrence of a cryptic species within the generitype T. crassa. Eudesme species (E. borealis, E. shandongensis and the generitype E. virescens) showed a sister relationship with the northern hemisphere Tinocladia (T. crassa, including a cryptic sister species T. pseudocrassa sp. nov., and T. sanrikuensis), whereas southern hemisphere Tinocladia (T. australis, T. falklandica, T. novae-zelandiae, and a cryptic species from New Zealand) nested in the Eudesme clade. Morphologically, Tinocladia species have been distinguished from Eudesme by their denser medullary filaments and more extensive subcortical layer, but our molecular phylogenetic analyses suggest that these features do not correlate with genetic differences. The cox3 sequence divergence between northern hemisphere Tinocladia and the lineage that includes Eudesme and southern hemisphere Tinocladia was comparable to or smaller than those within selected ectocarpalean genera. We therefore propose to merge Tinocladia with Eudesme and resurrect Eudesme crassa (Suringar) Okamura for T. crassa. Although the two independent lineages of T. crassa do not show marked morphological differences, they are genetically isolated even in sympatric populations. We therefore propose to treat them as independent species. In this paper we neotypify Tinocladia crassa (=Eudesme crassa), describe E. pseudocrassa sp. nov., and determine that the Californian population of E. crassa is an introduction from Northeast Asia.

HIGHLIGHTS

•A taxonomic revision of Eudesme and Tinocladia, based on genetic and morpho-anatomy, provides evidence to merge Tinocladia with Eudesme.

•The finding of cryptic species in New Zealand highlights the need for further taxonomic studies in this region.

•The genetic data have revealed the occurrence of a cryptic species within T. crassa in Japan.

Acknowledgements

We are grateful to Dr Eric C. Henry for his valuable comments on the manuscript, Drs Akira Kurihara, Hideaki Sasaki, Masahiro Suzuki and Masataka Fujiwara for collecting specimens of Japanese Tinocladia species, and Marnel Sherrenberg (Naturalis) for the investigations of Suringar collections, and Dr Yumiko Baba (Auckland Museum Herbarium) for providing the specimens of T. novae-zelandiae.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/09670262.2023.2183265

Supplementary fig. S1. Maximum likelihood tree based on chloroplast rbcL sequences (1413 bp). Numbers on branches indicate bootstrap values from ML analysis (left) and posterior probabilities from Bayesian analysis (BI, right). Only bootstrap values > 70% and posterior probability > 0.90 are shown. * and - show 100%/1.0 and < 70% / < 0.9 bootstrap and posterior probability.

Supplementary fig. S2. Holotype of Eudesme pseudocrassa. Collected at Mimaizaki, Ehime, Japan by T. Takeuchi on 26 April 2017 (SAP 115646).

Supplementary figs S3–S8. Morphology and anatomy of Tinocladia falklandica (=E. falklandica).

Supplementary fig. S3. Habit of specimen.

Supplementary fig. S4. Longitudinal section of thallus showing subcortical filaments (arrowhead) and assimilatory (arrow) filaments.

Supplementary fig. S5. Cross section of thallus showing medullar composed of densely packed medullary filaments (double arrowhead).

Supplementary fig. S6. Habit of old thalli.

Supplementary fig. S7. Cross section of thallus showing somewhat hollow medullary layer (arrow).

Supplementary fig. S8. Unilocular zoidangia. S3–S5, FLK 67, Saunders Island, collected on 21 January 2018 by J. Brodie and R. Mrowick. S6–8, FLK1239, collected on 19 February 2019 by J.B and R.M.

Supplementary table S1. Origin of samples and sequence data used for molecular analyses of chloroplast and mito-chondrial genes and nuclear rDNA region, including their database accession numbers. Newly determined sequences in the present study are indicated in bold. Sample codes in [KU-####] correspond to KU-MACC (Kobe University Macroalgal Culture Collection) strain code, and [KU-d####] corresponds to silica gel dried specimens housed at Kobe University Research Center for Inland Seas. [UC###] and [BM###] correspond to herbarium specimens housed at the University of California Herbarium (UC) and the Natural History Museum (BM), respectively.

Supplementary table S2. List of primers used for PCR and DNA sequencing of rbcL and cox3 genes.

Supplementary References for supplementary tables S1 and S2.

Additional information

Funding

This work was supported by the Darwin Plus [DPLUS68]. https://www.gov.uk/guidance/darwin-plus-applying-for-projects-in-uk-overseas-territories