Xin Wang

The freshwater red algal order Batrachospermales has a triphasic life history, of which the morphological characteristics of “Chantransia” stages are very similar to those of the genus Audouinella . In this study, two gametophyte stage specimens (CQM21 and CQW23) and four “Chantransia” stage specimens (CQ003, CQM22, CQW24, and GD247) were collected from Chongqing Municipality and Guangdong Province in China. Based on morphological data, all four “Chantransia” isolates were similar to A. pygmaea , whereas the morphological characteristics of CQM21 and CQW23 were in good agreement with the circumscription description of Sheathia dispersa . The rbc L and COI-5P analyses suggested that all six specimens belong to the genus Sheathia and supported the proposal of a new species, S. shaoguanensis sp. nov . Nevertheless, the five specimens from Chongqing (including the two gametophyte stage and three “Chantransia” stage specimens) were all assigned to S. dispersa . This represents the first report of the genus Sheathia in the Yangtze River.

Old trees function as enduring ecological legacies that preserve historical biodiversity within intensively human-modified landscapes, yet the relative influence of environmental versus anthropogenic drivers on their diversity remains unclear. Here, we aim to disentangle the joint effects of climate, urbanization intensity and cultural preservation on old-tree density and community composition. We analyzed a province-wide census of 21,733 old-tree individuals across 115 counties in Shanxi Province, China, encompassing species origin (native vs. nonnative) and growth form (trees vs. shrubs). Old-tree density was assessed using spatial simultaneous autoregressive error models, while compositional dissimilarity was quantified using generalized dissimilarity modeling. In total, 131 species were recorded, with four dominant species comprising more than 75% of all individuals. Old-tree density increased with mean annual temperature, human population density, and cultural heritage abundance, but declined sharply with cropland coverage. Driver importance varied among groups: native species were primarily governed by climatic conditions, nonnative species by land-use intensity, and tree-form old trees were positively associated with cultural heritage abundance, an effect absent in shrub-form old trees. Compositional dissimilarity was driven mainly by climatic gradients and spatial distance, with additional contributions from human-related variables, particularly for nonnative assemblages. Our findings demonstrate that climate and spatial processes establish the regional framework of old-tree community composition, while cultural and demographic contexts promote local retention of old trees. By explicitly integrating ecological filters with socio-cultural drivers, this study advances old-tree research through a large-scale empirical framework, providing both scientific insight and socially relevant guidance for conservation under land-use intensification and climate warming.

The “Chantransia” is an asexual reproductive stage in the life history of freshwater red algal orders Batrachospermales and Thoreales. Due to the lack of diagnostic features, samples at this stage need to be combined with morphological comparison and molecular phylogenetic analysis to determine their taxonomic affinities. In this study, five bluish “Chantransia” isolates collected from Guangdong and Shanxi Provinces of China were detected as belonging to two species. Among them, isolates HT2001 and HT2103 are the “Chantransia” of Virescentia guangxiensis and have the following features: microscopic thalli, the erect system consisting of filaments with cylindrical cells, undifferentiated into proximal and distal parts, and relatively small monosporangia (< 20 µm in diameter). The three other isolates (GD231, GD233 and GD234), from Dinghu Mountain of Guangdong Province, are characterized by the following features: microscopic thalli with a well-developed prostrate system composed of creeping and loosely aggregated filaments, and the erect system consisting of filaments with cylindrical cells and small monosporangia (< 20 µm in diameter). Phylogenetic analyses based on rbcL and COI-5P supported the proposal of a new species—V. dinghuensis sp. nov. The description of this new species contributes to a more comprehensive understanding of the species diversity and biogeographical distribution of the genus Virescentia in China.