A phylum of mostly freshwater eukaryotic organisms, traditionally known as yellow-green algae, that possess carotenoid pigments (including xanthins), which are responsible for their colour, in addition to chlorophylls. Xanthophytes occur in a variety of forms—unicellular, colonial, filamentous, and siphonaceous; motile cells have two unequal-sized flagella. Storage products are oil and the polysaccharide chrysolaminarin. Xanthophytes are included in a eukaryotic assemblage known as the stramenopiles.