The Ulvophyceae or ulvophytes are a class of green algae,[3] distinguished mainly on the basis of ultrastructural morphology, life cycle and molecular phylogenetic data.

Other well-known members include Caulerpa, Codium, Acetabularia, Cladophora, Trentepohlia and Monostroma.

Others, such as Rhizoclonium, Pithophora and some species of Cladophora live in fresh water[5] and in some areas are considered weeds.

Molecular phylogenetic evidence suggests that macroscopic growth was achieved independently in the various major lineages of Ulvophyceae (Ulvales-Ulotrichales, Trentepohliales, Cladophorales, Bryopsidales and Dasycladales).

Cladophorales Blastophysa Dasycladales Bryopsidales Trentepohliales Ignatius clade Ulvales Phaeophila, Bolbocoleon Ulotrichales Desmochloris, Halochlorococcum Scotinosphaerales Oltmannsiellopsidales