The class Ulvophyceae (named after the type genus Ulva) is a diverse group of green algae found worldwide, primarily on marine coasts attached to substrates. However, many species inhabit freshwater, brackish environments, or even terrestrial settings, where they can withstand desiccation.

Typically simple organisms, Ulvophyceae species vary widely: some are immobile unicellular, others are filamentous, colonial, laminar, or even form complex structures. Certain lineages exhibit giant cell formation, and some unicellular species grow to several centimeters. The group is defined by cellular characteristics, especially chloroplasts, flagellar insertion, and cell division. Their life cycles often include two or more generations, typically featuring a mobile, flagellated unicellular phase.