New molecular evidence of the genus Hydrurus (Chrysophyceae) and descriptions of Hydrurus foetidus (Villars) Trevisan on the basis of morphology and phylogeny

Background The genus Hydrurus contains a solitary species, Hydrurus foetidus. Its thalli exhibit a remarkable structure, consisting of a firm central axis surrounded by peripheral branches, all enveloped within a viscous, gelatinous coating. Molecular data pertaining to the genus Hydrurus are scarce, necessitating further investigation into its phylogenetic relationships. New information A new site with benthic freshwater alga Hydrurus foetidus (Villars) Trevisan has been discovered in the Fenhe River in Shanxi Province, China. The physical and chemical parameters of water were meticulously measured and documented. Detailed morphological observations were conducted on the specimen, measuring different cell categories. The SSU, LSU, ITS and rbcL DNA sequence data of H. foetidus collected from Shanxi were determined. An extensive three-gene phylogenetic tree was constructed, revealing a strong relationship between the specimen in this study and H. foetidus specimen from Norway. Time-calibrated molecular phylogenetic analysis further indicated that the genus Hydrurus diverged approximately 125 million years ago (Early Cretaceous), while the two H. foetidus strains from Shanxi, China and Norway diverged approximately 6 million years ago (Neogene). The results of this study supplement new molecular evidence for H. foetidus and contribute significantly to our understanding of the geographical distribution and evolutionary history ofthe genus Hydrurus.