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

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. The H. foetidus thalli exhibited a unique structure, consisting of a firm central axis surrounded by peripheral branches, all encapsulated by a viscous gelatinous coating. Detailed morphological observations were conducted on the specimen, measuring of different cell categories. The SSU, LSU, ITS, and rbc L 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 of the genus Hydrurus .