Morphological and molecular study identifies new freshwater red alga from South China

A morphological and molecular study of six freshwater red algal specimens from China identified a new species in the genus Sheathia and recorded S. dispersa at a new locality. The specimens were collected in Chongqing and Guangdong and included two gametophytes and four microscopic “Chantransia” stages analyzed with the rbcL and COI-5P markers.

Five isolates, CQ003, CQM21, CQM22, CQW23 and CQW24, were collected from the levees of the Yangtze River in Fengjie County, Chongqing. Sequence comparisons placed them with previously reported specimens of S. dispersa from China, Nepal, Japan and the United States. Their uncorrected rbcL pairwise distances ranged from 0% to 1%, corresponding to zero to 12 base-pair differences, while distances from these isolates to other Sheathia species ranged from 2% to 10%, or 25 to 115 base pairs.

The COI-5P alignment also placed the five Chongqing isolates with S. dispersa. The mean pairwise distance between samples from China and the United States was 1%. Maximum-likelihood and Bayesian analyses of both markers produced broadly similar relationships. In the rbcL tree, the isolates joined the S. dispersa clade with support of 1.00 Bayesian posterior probability and 97% maximum-likelihood bootstrap value; the corresponding COI-5P values were 1.00 and 100%.

The rbcL dataset included 63 aligned sequences and 1,207 nucleotides, of which 351 were variable and 297 were parsimony-informative. The COI-5P alignment was 567 base pairs long, with 206 variable sites, including 186 parsimony-informative sites. The two gametophyte specimens from Chongqing, CQM21 and CQW23, were also morphologically consistent with S. dispersa. CQM21 was identified as male and CQW23 as female.

Both gametophytes had spherical to barrel-shaped whorls measuring 409–709 µm in diameter. Their main axes were corticated by two or three layers of filaments composed only of cylindrical cells. The male plant had spherical, terminal spermatangia measuring 5.5–7.3 µm in diameter. The female plant had spherical, exserted carposporophytes measuring 103–353 µm in diameter, an erect three- to five-celled carpogonial branch, carpogonia 8.9–13.3 µm long and 5.6–6.7 µm in diameter, and clavate trichogynes.

The other three Chongqing isolates and the Guangdong specimen had the simpler form assigned to the “Chantransia” stage. Across these four specimens, the thalli were brownish tufts composed of branched filaments, with vegetative cells 22.1–77.8 µm long and 5.3–17.8 µm in diameter. Monosporangia were obovoidal, occurring singly or in clusters at branch tips, and measured 8.4–21.1 µm long and 6.3–13.3 µm in diameter. Their filaments were morphologically similar to Audouinella pygmaea, illustrating why molecular evidence was needed for reliable identification.

Specimen GD247, collected in November 2020 from the surface of a stone in flowing water at Guangdong Grand Canyon in Shaoguan, formed a distinct lineage in both phylogenetic analyses. It was sister to the clade containing S. yedoensis from Japan, with support values of 1.00 and 100% for the rbcL analysis and 1.00 and 99% for COI-5P. Its rbcL distance from other Sheathia species was 4.7%, compared with an intraspecific value of 0.2%. Its COI-5P distance from other Sheathia species was 9.7%, whereas reported intraspecific distances were 0–1%.

On the basis of these molecular and morphological results, the authors described GD247 as Sheathia shaoguanensis sp. nov. The species is currently known only from its “Chantransia” stage. The holotype, GKD-GD20247, was prepared from strain GD247 and deposited at the herbarium of Shanxi Vocational University of Engineering Science and Technology. Its diagnostic sequences are rbcL accession PZ319268 and COI-5P accession PZ321420. The epithet refers to Shaoguan, China.

The reported species has hemispherical thalli 3.6–9.8 mm high, lateral branches developing at angles of 25° or less, main-branch vegetative cells 22.1–33.7 µm long and 5.3–7.4 µm in diameter, and numerous ovoid monosporangia measuring 8.4–13.7 µm long and 6.3–11.6 µm in diameter. No gametophyte of S. shaoguanensis was found, so its larger-scale morphology and cortication could not be established directly. Its features overlap with those of S. yedoensis in thallus height, vegetative-cell dimensions and monosporangial size, meaning the two cannot be separated reliably by morpho-anatomical characteristics alone.

Although most specimens collected in the study were in the “Chantransia” stage, the molecular analyses distinguished the five Chongqing specimens as gametophyte and “Chantransia” stages of S. dispersa and identified GD247 as a new species. The Chongqing findings extended the recorded Chinese distribution of S. dispersa to a third location, following earlier records from Taiwan and Yunnan, and showed that the species was growing on metal stairs and a cement embankment along the Yangtze River.

Subject of Research: Taxonomic and phylogenetic study of freshwater red algae in South China

Article Title: Sheathia shaoguanensis sp. nov. ( Batrachospermales , Rhodophyta ), a new freshwater red algal species from South China

Article References: Han, J.-F., Wang, X., Yin, B., & Xie, S.-L. (2026). Sheathia shaoguanensis sp. nov. (Batrachospermales, Rhodophyta), a new freshwater red algal species from South China. PhytoKeys, 277, 25-40. https://doi.org/10.3897/phytokeys.277.198746

Image Credits: AI Generated

DOI: 10.3897/phytokeys.277.198746

Keywords: Sheathia shaoguanensis, Sheathia dispersa, freshwater red algae, Rhodophyta, Batrachospermales, molecular phylogeny, rbcL, COI-5P, South China, species delimitation, Sheathia, shaoguanensis