An order of the *Chlorophyceae
containing pseudoparenchymatous thalloid algae (e.g. Ulva), characteristically found in marine and brackish waters. The sheetlike thallus is formed by division in two planes of a filament that initially resembles those of the *Ulotrichales
. The Ulvales are consequently often placed in this order. There is an isomorphic alternation of generations in some species.