Sporochnus keyari sp. nov. (Sporochnales, Phaeophyceae) from Japan

ABSTRACT

In the genus Sporochnus (Sporochnales, Phaeophyceae), Okamura reported S. radiciformis and S. scoparius in Japan in 1922; however, S. scoparius was later synonymized with S. radiciformis, as Okamura’s S. radiciformis was considered to be a young stage of S. scoparius. Therefore, only one species, S. radiciformis, has been recognized in Japan, until the reported occurrence of a second species, S. dotyi, and suggestion that the species identified as S. radiciformis in Japan was genetically distinct from true S. radiciformis described from Australia. We now report findings that based on molecular phylogeny (atpB, rbcL, atp6, cox3) and morpho-anatomical analyses confirming that the common Japanese Sporochnus species is distinct from true S. radiciformis, and we therefore describe a new species, S. keyari sp. nov. This new species differs from S. radiciformis in having less-branched erect thalli, longer terminal assimilatory filaments (trichothallic hairs), and larger unilocular zooidangia, and from S. bolleanus in having more robust thallus axes. In gross morphology, S. keyari is distinguished from S. dotyi, which is also distributed in Japan, in having more slender thalli and lacking greenish structural colour of the assimilatory filaments. In culture, unizoids (zoospores) released from unilocular zooidangia developed into monoicous gametophytes forming antheridia and oogonia at the distal ends of the filaments. Actual sexual fusion was not observed, but presumably fertilization occurred within oogonia and new sporophytes developed in situ within oogonia. Sporophytes were at first uniseriate, but later formed terete thalli by trichothallic growth, with terminal assimilatory filaments.

KEYWORDS:

• Life history
• molecular phylogeny
• morphology
• new species
• taxonomy

ACKNOWLEDGEMENTS

We are grateful to Akihiro Nagata, Hironori Shimabukuro, Hiroki Tomioka, and Yuki Miyachi-Tomioka for collections of Sporochnus keyari. We are also grateful to Eric C. Henry for valuable comments on the manuscript, Yola Metti for her assistance in examining Sporochnus specimens housed in the Botanic Gardens of Sydney, and Kazuhiro Kogame and Takeshi Abe for examination of Sporochnus specimens housed in SAP.

DISCLOSURE STATEMENT

No potential conflict of interest was reported by the authors.

SUPPLEMENTARY MATERIAL

Supplemental data for this article can be accessed online at https://doi.org/10.1080/00318884.2024.2355599