Derbesia is a genus of green algae, specifically of the Derbesiaceae. The plant was originally known from different names applied to its larger sporophyte, Derbesia, and its less conspicuous gametophyte, Halicystis. Derbesia was successfully cultured in the laboratories of German phycologist Peter Kornmann to learn that both it and the plant Halicystis were different parts of the life cycle of the same organism.