The Ulvophyceae or Ulvophytes are class of green algae, distinguished mainly on the basis of ultrastructural morphology. The sea lettuce

Sea lettuce

The sea lettuces comprise the genus Ulva, a group of edible green algae that is widely distributed along the coasts of the world's oceans. The type species within the genus Ulva is Ulva lactuca Linnaeus, "lactuca" meaning lettuce...

, Ulva, belongs here. Other well-known members include Ulothrix

Ulothrix

In taxonomy, Ulothrix is a genus of algae, specifically of the Ulotrichaceae.Ulothrix is a genus of filamentous green algae, generally found in fresh and marine water. Its cells are normally as broad as they are long, and they thrive in the low temperatures of spring and winter. They become...

and Acetabularia

Acetabularia

Acetabularia is a genus of green algae, specifically of the Polyphysaceae family, Typically found in subtropical waters, Acetabularia is a single-celled organism, but gigantic in size and complex in form, making it an excellent model organism for studying cell biology...

.
The Ulvophytes are diverse in their morphology

Morphology (biology)

In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....

 and their habitat

Habitat (ecology)

A habitat is an ecological or environmental area that is inhabited by a particular species of animal, plant or other type of organism...

. Most are seaweed

Seaweed

Seaweed is a loose, colloquial term encompassing macroscopic, multicellular, benthic marine algae. The term includes some members of the red, brown and green algae...

s such as those listed above. Others, such as Cladophora

Cladophora

Cladophora is a genus of reticulated filamentous Ulvophyceae . The genus Cladophora contains many species that are very hard to tell apart and classify, mainly because of the great variation in their appearances, which is affected by habitat, age and environmental conditions...

, Rhizoclonium

Rhizoclonium

In taxonomy, Rhizoclonium is a genus of algae, specifically of the Cladophoraceae.-Scientific databases:* * *...

and Pithophora

Pithophora

In taxonomy, Pithophora is a genus of algae, specifically of the Cladophoraceae.-Scientific databases:* * *...

live in fresh water and in some areas are considered weed

Weed

A weed in a general sense is a plant that is considered by the user of the term to be a nuisance, and normally applied to unwanted plants in human-controlled settings, especially farm fields and gardens, but also lawns, parks, woods, and other areas. More specifically, the term is often used to...

s.