Phycology

This study analyzes the diversity of thin filamentous cyanobacteria from the volcanic Lake Terkhiin-Tsagaan, Mongolia. We isolated and characterized two strains from benthic samples collected from the lake. Using light microscopy, phylogenetic analysis of 16S rRNA gene sequences, and examination of the secondary structures of the 16S–23S ITS helices, we describe a new genus, Dgebuadzia, and a new species, Dgebuadzia mongoliensis. The 16S rRNA gene similarity to Phormidesmis was below the genus-level threshold (89.5% to P. mollis NIES-2126; minimum 94.19% to non-mollis Phormidesmis species), and the strains formed a well-supported monophyletic clade (BI/ML = 1/100) that is distinct from all other Leptolyngbyaceae included in the analysis. The strains also differed from Phormidesmis in the secondary structure of the Box-B and V3 helix. The new genus is closely related to P. arctica, a taxon whose original description is nomenclaturally invalid and which therefore cannot be formally transferred, although its phylogenetic position places it within the Dgebuadzia lineage. The data presented here contribute to our understanding of the diversity of thin filamentous cyanobacteria and expand current knowledge of the algal flora of Mongolian volcanic lakes.

We examined 13 strains of marine monoraphid diatoms belonging to the genera Schizostauron, Astartiella, and Achnanthes, isolated from the South China Sea near Viet Nam, with the use of light, fluorescent and electron microscopy, and molecular methods. Based on our investigation, two new species of Astartiella are described: Astartiella triundulata and Astartiella zinaidae. A morphological comparison with close species is provided, and the results of molecular analysis are discussed. Schizostauron strains were identified as S. trachyderma: the cryptic diversity and genetic variability within this genus are examined. Data on geographical distribution of these taxa are presented. A total fatty acid profile was obtained for both Schizostauron and Astartiella strains, and the results are discussed as well.

Marine green tides are ecological phenomena caused by the massive proliferation of green macroalgae, particularly species of the genus Ulva, whose frequency and geographic extent have increased worldwide. These events are commonly associated with interacting anthropogenic and environmental drivers, including nutrient enrichment, coastal modification, climatic variability, and hydrodynamic retention. In Chile, green tides have been reported in several coastal bays, including Coliumo Bay; however, systematic studies on their species composition have been largely restricted to Algarrobo Bay, another coastal upwelling-influenced embayment located in central Chile. In this study, we investigated the laminar Ulva species associated with recurrent summer green tides at Dichato Beach, located in Coliumo Bay, Biobío Region, Chile. Twenty specimens were collected during the 2025 green tide and analyzed using an integrative approach that combined detailed morphological characterization with molecular analyses based on the tufA and ITS1 markers. Our results revealed the presence of three laminar, foliose, and distromatic taxa: Ulva australis, Ulva stenophylloides, and an unresolved lineage designated as Ulva sp. (D4). These taxa showed consistent morphological differentiation in traits such as thallus color, frond margin morphology, and perforation patterns. Phylogenetic analyses further indicated that Ulva sp. (D4) did not cluster with any described species included in the analyses, supporting its recognition as a distinct lineage that may represent an undescribed taxon. This study expands the known distribution of U. australis and U. stenophylloides in the southeastern Pacific and highlights the relevance of integrative taxonomy for resolving green tide diversity and supporting future ecological monitoring and management strategies in Chilean coastal systems.