Green algae classes

The Ulvophyceae or ulvophytes are a class of green algae, distinguished mainly on the basis of ultrastructural morphology, life cycle and molecular phylogenetic data. The sea lettuce, Ulva, belongs here. Other well-known members include Caulerpa, Codium, Acetabularia, Cladophora, Trentepohlia and Monostroma.

The Chlorophyceae, also known as chlorophycean algae, are one of the classes of green algae, within the phylum Chlorophyta. They are a large assemblage of mostly freshwater and terrestrial organisms; many members are important primary producers in the ecosystems they inhabit. Their body plans are diverse and range from single flagellated or non-flagellated cells to colonies or filaments of cells. The class Chlorophyceae has been distinguished on the basis of ultrastructural morphology; molecular traits are also being used to classify taxa within the class.

Charophyceae is a class of charophyte green algae. AlgaeBase places it in division Charophyta. Extant (living) species are placed in a single order Charales, commonly known as "stoneworts" and "brittleworts". Fossil members of the class may be placed in separate orders, e.g. Sycidiales.

Zygnematophyceae (or Conjugatophyceae) is a class of green algae in the paraphylum streptophyte algae, also referred to as Charophyta, consisting of more than 4000 described species. The Zygnematophyceae are the sister clade of the Embryophyta (land plants).

The Trebouxiophyceae, also known as trebouxiophytes, are a class of green algae, in the division Chlorophyta. Members of this class are single-celled, colonial, or multicellular and are found in freshwater, terrestrial or marine habitats worldwide. Many taxa in the Trebouxiophyceae form symbiotic relationships with other organisms; in particular, the majority of phycobionts within lichens are trebouxiophytes. A number of taxa have also lost the ability to photosynthesize, and have evolved to become parasitic; examples include Prototheca and Helicosporidium.

The Mesostigmatophyceae are a class of basal green algae found in freshwater. In a narrow circumscription, the class contains a single genus, Mesostigma. AlgaeBase then places the class within its circumscription of Charophyta. A clade containing Chlorokybus and Spirotaenia may either be added, or treated as a sister, with Chlorokybus placed in a separate class, Chlorokybophyceae. When broadly circumscribed, Mesostigmatophyceae may be placed as sister to all other green algae, or as sister to all Streptophyta.

Coleochaetophyceae is a class of charophyte algae related to land plants (only Zygnematophyceae is closer). There are about 35 known species, and are predominantly found in freshwater where they live periphytic on the surface of aquatic plants, plastic bags and pebbles in the shallow littoral zone of freshwater lakes. These are small (<200 μm) disc-shaped or filamentous species, and have true multicellular organisation with sexual and asexual reproduction. The discs never develop beyond a two-dimensional organization. Their mitogenome is the most intron rich organelle among the streptophyte al

The prasinophytes are a group of unicellular green algae. Prasinophytes mainly include marine planktonic species, as well as some freshwater representatives. The prasinophytes are morphologically diverse, including flagellates with one to eight flagella and non-motile (coccoid) unicells, as well as dormant or cyst stage phycoma. The cells of many species are covered with organic body scales; others are naked. Well studied genera include Ostreococcus, considered to be the smallest (ca. 0.95 μm) free-living eukaryote, and Micromonas, both of which are found in marine waters worldwide. Prasinophy

Pedinophyceae is a class of green algae in the division Chlorophyta.

REDIRECT Klebsormidiales

thumb|right|Bryopsis plumosa Bryopsidophyceae is an unaccepted class of chlorophyte green algae. The order Bryopsidales has been included in the class Ulvophyceae. However, several recent phylogenomic studies have recovered Bryopsidales as sister clade to the Chlorophyceae.

Pyramimonadophyceae is a class of green algae in the division Chlorophyta. In 2024, one of its former members, Pseudoscourfieldiales, was classified into the new class Pseudoscourfieldiophyceae.

The Palmophyllophyceae are a class of green algae consisting of the Palmophyllales and Prasinococcales.