A TAXONOMIC REVISION OF THE CHINESE AUDOUINELLA DAVIESII (DILLWYN) WOELKERLING (ACROCHAETIALES, RHODOPHYTA)

The marine taxa of the genus Audouinella comprise a group of filamentous red algae typically epiphytic on macroalgae. Characterized by their simple morphology and high diversity of morphospecies, they represent one of the most problematic groups in red algal taxonomy. In this study, Audouinella specimens collected from the Yellow Sea and Bohai Sea were successfully isolated, purified, and cultured, and detailed taxonomic studies were conducted. The results showed the following: (1) Morphologically, the specimens from these waters are consistent with the previously reported Audouinella daviesii (Dillwyn) Woelkerling in China. The thalli are red and tufted, 1-4 mm in height, and attach to the host by a basal disc composed of creeping filaments. Erect filaments are irregularly branched with thicker main axes. The cells are cylindrical, 15-30 μm long and 7-15 μm wide, with ribbon-like parietal plastids. Monosporangia are ovoid, mostly clustered in corymbs at the axils of branchlets, occasionally on the lateral sides of branches, or rarely solitary and lateral. (2) Molecular phylogenetic analyses based on rbcL and COI-5P genes revealed that this alga clustered into a single clade with Colaconema daviesii (Dillwyn) Stegenga from Canada and Chile with no sequence divergence, supporting the taxonomic revision of the Chinese Audouinella daviesii to Colaconema daviesii. This study reports the first molecular data for a species of the order Acrochaetiales in China and corroborates the international taxonomic revision of transferring this species to the genus Colaconema. The results also reveal that extensive taxonomic issues remain within the marine Audouinella, and the taxonomic status of many morphospecies requires further investigation incorporating molecular data. The isolation and purification method for parasitic filamentous algae provides a new approach for future studies on similar epiphytic and parasitic algae, offering cultivation techniques and a taxonomic theoretical basis for further research on algae of the order Acrochaetiales.