Background: Order Chaetophorales currently includes six families, namely Schizomeridaceae, Aphanochaetaceae, Barrancaceae, Uronemataceae, Fritschiellaceae, and Chaetophoraceae. The phylogenetic relationships of Chaetophorales have been inferred primarily based on short and less informative rDNA sequences. This study aimed to phylogenetically reconstruct order Chaetophorales and determine the taxonomic scheme and to further the current understanding of the evolution of order Chaetophorales.Results: In the present study, seven complete and five fragmentary chloroplast genomes were harvested. Phylogenomic and comparative genomic analysis were performed to determine the taxonomic scheme within Chaetophorales. Consequently, Oedogoniales was found to be a sister to a clade linking Chaetophorales and Chaetopeltidales. Schizomeriaceae, and Aphanochaetaceae clustered into a well-resolved basal clade in Chaetophorales, inconsistent with the results of phylogenetic analysis based on rDNA sequences. Comparative genomic analyses revealed that the chloroplast genomes of Schizomeriaceae and Aphanochaetaceae were highly conserved and homologous, highlighting the closest relationship in this order. Germination types of zoospores precisely correlated with the phylogenetic relationships.Conclusions: chloroplast genome structure analyses, synteny analyses, and zoospore germination analyses were concurrent with phylogenetic analyses based on the chloroplast genome, and all of them robustly determined the unique taxonomic scheme of Chaetophorales and the relationships of Oedogoniales, Chaetophorales, and Chaetopeltidales.

Tibet is a very important biodiversity hot spot in China and the diatom flora of this region has drawn a lot of attention. Diatom samples were collected from several places across Tibet. During research on the biodiversity of diatoms from Tibet, one Achnanthidium species showed unique features compared with other known taxa. It has linear-lanceolate valves with rounded apices, tear-drop shaped proximal raphe ends and ?-shaped distal raphe ends. The most distinctive character of this species, however, is the shape of areolae; since this species has nearly round external areolar openings on the valve face but more typical slit-like areolae present on the mantle. Here we describe it as new to science as Achnanthidium tibeticum Y. Liu & Kociolek. We compare this new species with other, similar taxa within the genus.

Phytoplankton are the main primary producers in aquatic ecosystems and play an important role in food web and geochemical cycles. Its diversity, community structure, and assembly process are influenced by several factors. Among these factors, climate change and human synergistic changes in water physicochemical factors and nutrient levels are the main causes. Alpine lake ecosystems are relatively weak and extremely sensitive to global climate change. However, the impact of climate change on phytoplankton in Qinghai-Tibet Plateau (QTP) lakes and their responses are still unclear. In this study, we systematically analyzed the diversity, environmental drivers, and assembly process of phytoplankton community in the central QTP lakes. The phytoplankton of these lakes can be primarily distinguished into freshwater and brackish types, with significant differences in species diversity and community dissimilarity. Both types shared nearly same key environmental factors that significantly affecting phytoplankton such as EC, and brackish lakes were also positively correlative with TN, Ca and Si. Stochastic process was predominant in phytoplankton assembly because of the harsh environmental condition. Additionally, freshwater and brackish lakes were dominated by dispersal limitation and heterogeneous selection respectively. Alpine lakes had significant EC thresholds, and their diversity and assembly processes changed significantly around the thresholds. Owing to warming and moistening of QTP during the past decades, some significant changes have occurred, such as gradual decrease in lake EC. The present findings have important implications for understanding and predicting the response of lake phytoplankton communities to climate change and for making decisions to protect the ecological resources of alpine lakes.