Abstract
Culture strains of unicellular Ochromonas smithii and O. itoi isolated from yellow snow, which appeared near the beech forests of Mt. Gassan (Yamagata Pref., Japan), were provided for examining their morphological and physiologial properties as well as the systematic position inferred from the 18SrDNA gene sequences. They showed the unique cell shapes with one to four spines on the cell surface and the peaks at 5 or 10 C on their temperature-photosynthesis curves. From the phylogenetic tree, we could recognize that they made a clade with an Anterctic Ochromonas and multicellular Hydrurus foetidus and Chrysonebula holmesii, which released zoospores with the closely similar cell shapes and grew well in the cold water rivers at winter season. It is possible to be present a phylogenetic lineage composed of the cold adaptative chrysophyceans.
