(yellow-green algae) A division consisting mainly of freshwater and terrestrial *algae
, including unicellular, colonial (palmelloid), filamentous, and siphonaceous forms. They are characterized by having disclike yellow-green plastids (due to the large amounts of carotenoids present) and by accumulating oil and leucosin rather than starch. The motile stages have two unequal flagella (one flimmer and one smooth flagellum) hence the older name Heterokontae. The cell wall is divided into two halves but this character is not obvious except in the filamentous forms, where disruption results in a number of Η-shaped fragments.