Nikulin V.Yu., Sushchenko R.Z., Nikulin A.Yu., Bagmet V.B., Abdullin Sh.R., Gontcharov A.A.
Phycologia 2026: 1-14
Four strains of the coccoid green algal genus Coelastrella (Scenedesmaceae, Sphaeropleales) were isolated from moss-covered rocks and soils in the southern Russian Far East (Primorsky Territory and Iturup Island). An integrative taxonomic approach combining light and scanning electron microscopy, confocal laser microscopy, multi-locus phylogeny (nuclear SSU+ITS rDNA region and chloroplast tufA), ITS2 secondary-structure analysis, and three molecular species-delimitation methods (PTP, ASAP, GMYC) were applied. Two strains (VCA-307 and VCA-308) formed a robust lineage within the ‘core Coelastrella’ clade, being sister to C. striolata, C. multistriata, and C. corcontica. Sequence divergences (4.06–13.13% in the ITS rDNA region) and a unique compensatory base change in the conserved barcode region of ITS2 helix III (A–U pair) clearly separated them from all described congeners. All delimitation algorithms recognized these strains as a distinct species-level cluster. Based on morphology (16–24 meridional rows of rounded warts, small lemon-shaped to ellipsoid cells 4.9–12.6 × 3.7–10.7 μm, lobed chloroplast in mature cells) and molecular data, the strains are described here as Coelastrella iturupiensis sp. nov. The remaining two strains represent the first records of the Arctic species C. polaris (VCA-309) and C. affinis (VCA-310) outside Yakutia and the Moscow Region, respectively. These findings substantially expand the known diversity and distribution of Coelastrella in Northeast Asia.
