Life cycle and molecular phylogeny of Vaucheria piloboloides (Vaucheriales, Xanthophyceae) from Sado Island, Japan

The siphonous, yellow–green alga Vaucheria piloboloides (Vaucheriales, Xanthophyceae) is the type species of the section Piloboloideae and is widely reported worldwide. Despite its taxonomic importance and broad range distribution, its detailed life cycle and molecular phylogenetic position are unknown. In the present study, we established culture strains of V. piloboloides collected from Sado Island, Niigata Prefecture, Japan, and examined its morphology, life cycle and phylogenetic position based on rbcL sequences. The morphology of the gametangia and aplanosporangia (asexual sporangia) of our samples, along with their monoecious nature, resembled that of V. piloboloides from the Atlantic coast, including the type locality. The rbcL phylogenetic analysis demonstrated that our sample formed a clade with other Piloboloideae species, supporting the current sectional scheme of Vaucheria. Under culture conditions, our samples exhibited a monophasic life cycle. Development of gametangia was observed in any culture conditions, whereas development of aplanosporangia could be induced by low salinity (salinity = 24).