Transfer of Pilinia from Ectocarpales to Ishigeales (Phaeophyceae) with proposal of Piliniaceae fam. nov., and taxonomy of Porterinema in Ectocarpales

ABSTRACT

Molecular phylogeny based on concatenated sequences of chloroplast atpB, psaA, psbA, psbC and rbcL genes indicates that the filamentous brown alga Pilinia rimosa is phylogenetically distant from the Ectocarpales, in which it has been classified (as Waerniella lucifuga). In the tree, Pilinia was sister to the clade comprised of Ishige and Petroderma (Ishigeales) supported by high statistical values. Observations of unialgal P. rimosa cultures originating from Helgoland (Germany), England (UK), Woods Hole (USA) and Newfoundland (Canada) showed a direct type of life history with reproduction by characteristic unilocular zoidangia typically forming only four zoids. Despite the description of plurilocular zoidangia in Kuckuck’s account as well as in later publications, we conclude that those observations were based on misinterpretation of the very small unilocular zoidangia formed in series, often with longitudinal walls between zoidangia. Pilinia rimosa grows in caves or crevices in rocks, and on walls or wood pilings in deep shade in the upper intertidal and spray zone, and is therefore regarded as a marine species, but it could also survive and mature in freshwater medium. We propose the establishment of a new family Piliniaceae for Pilinia and place it in Ishigeales. Molecular and morphological analysis of the culture strains, SAG 124.79 and SAG 2381, identified as the euryhaline alga Porterinema fluviatile, indicated that SAG 124.79 is in fact P. rimosa. However, SAG 2381 is true P. fluviatile, also displaying the characteristic plurilocular zoidangia. Porterinema was shown to be a member of the Chordariaceae, Ectocarpales sensu lato.

KEYWORDS:

• Ectocarpales
• Ishigeales
• molecular phylogeny
• Pilinia
• Piliniaceae
• Porterinema
• taxonomy

Acknowledgements

We are grateful to Maike Lorenz for providing SAG Porterinema cultures.

Disclosure statement

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

Supplementary information

The following supplementary material is accessible via the Supplementary Content tab on the article’s online page at https://doi.org/10.1080/09670262.2021.1970235

Supplementary fig. S1. Maximum likelihood tree based on DNA sequences of chloroplast rbcL gene (1414 bp). Numbers on branches indicate bootstrap values (%) from ML analysis (left) and posterior probabilities from Bayesian analysis (right). Asterisk (*) indicates 100% bootstrap (ML) and 1.00 posterior probability (Bayesian) values. Only bootstrap values ≥ 70% and posterior probabilities ≥ 0.90 are shown.

Supplementary table S1. Origin of specimens and sequence data used for molecular analyses of chloroplast and mitochondrial genes, including their database accession numbers. Sample codes [KU-####] correspond to KU-MACC (Kobe University Macroalgal Culture Collection) strain codes, and [KU-d####] corresponds to silica-gel dried specimens housed at Kobe University Research Center for Inland Seas. Accession codes of sequences newly determined in the present study are indicated in bold.

Author contributions

Hiroshi Kawai: Morphological studies, culture experiments, drafting and editing manuscript; Takeaki Hanyuda: genetic analyses; Eric C. Henry: collection of Pilinia specimens, establishment of culture strains, morphological observations by light microscopy and TEM, and manuscript editing.