Chlorophyta is a taxon of green algae informally called chlorophytes. The name is used in two very different senses, so care is needed to determine the use by a particular author. In older classification systems, it is a highly paraphyletic group of all the green algae within the green plants (Viridiplantae) and thus includes about 7,000 species of mostly aquatic photosynthetic eukaryotic organisms. In newer classifications, it is the sister clade of the streptophytes/charophytes. The clade Streptophyta consists of the Charophyta in which the Embryophyta emerged. In this latter sense the Chlorophyta includes only about 4,300 species. About 90% of all known species live in freshwater. Like the land plants, green algae contain chlorophyll a and chlorophyll b and store food as starch in their plastids.
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 green algae are a group consisting of the Prasinodermophyta and its unnamed sister which contains the Chlorophyta and Charophyta/Streptophyta. The land plants (Embryophytes) have emerged deep in the Charophyte alga as sister of the Zygnematophyceae. Since the realization that the Embryophytes emerged within the green algae, some authors are starting to include them. The completed clade that includes both green algae and embryophytes is monophyletic and is referred to as the clade Viridiplantae and as the kingdom Plantae. The green algae include unicellular and colonial flagellates, most with two flagella per cell, as well as various colonial, coccoid and filamentous forms, and macroscopic, multicellular seaweeds. There are about 22,000 species of green algae. Many species live most of their lives as single cells, while other species form coenobia (colonies), long filaments, or highly differentiated macroscopic seaweeds.
Streptophyta, informally the streptophytes, is a clade of plants. The composition of the clade varies considerably between authors, but the definition employed here includes land plants and all green algae except the Chlorophyta and the more basal Prasinodermophyta.
Charophyta is a group of freshwater green algae, called charophytes, sometimes treated as a division, yet also as a superdivision or an unranked clade. The terrestrial plants, the Embryophyta emerged deep within Charophyta, possibly from terrestrial unicellular charophytes, with the class Zygnematophyceae as a sister group.
Viridiplantae constitute a clade of eukaryotic organisms that comprises approximately 450,000–500,000 species that play important roles in both terrestrial and aquatic ecosystems. They include the green algae, which are primarily aquatic, and the land plants (embryophytes), which emerged from within them. Green algae traditionally excludes the land plants, rendering them a paraphyletic group. However it is accurate to think of land plants as a kind of alga. Since the realization that the embryophytes emerged from within the green algae, some authors are starting to include them. They have cells with cellulose in their cell walls, and primary chloroplasts derived from endosymbiosis with cyanobacteria that contain chlorophylls a and b and lack phycobilins. Corroborating this, a basal phagotroph archaeplastida group has been found in the Rhodelphydia.
The Archaeplastida are a major group of eukaryotes, comprising the photoautotrophic red algae (Rhodophyta), green algae, land plants, and the minor group glaucophytes. It also includes the non-photosynthetic lineage Rhodelphidia, a predatorial (eukaryotrophic) flagellate that is sister to the Rhodophyta, and probably the microscopic picozoans. The Archaeplastida have chloroplasts that are surrounded by two membranes, suggesting that they were acquired directly through a single endosymbiosis event by phagocytosis of a cyanobacterium. All other groups which have chloroplasts, besides the amoeboid genus Paulinella, have chloroplasts surrounded by three or four membranes, suggesting they were acquired secondarily from red or green algae. Unlike red and green algae, glaucophytes have never been involved in secondary endosymbiosis events.
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. The cells of many species are covered with organic body scales; others are naked. Well studied genera include Ostreococcus, considered to be the smallest free-living eukaryote, and Micromonas, both of which are found in marine waters worldwide. Prasinophytes have simple cellular structures, containing a single chloroplast and a single mitochondrion. The genomes are relatively small compared to other eukaryotes . At least one species, the Antarctic form Pyramimonas gelidicola, is capable of phagocytosis and is therefore a mixotrophic algae.
Oltmannsiellopsidales is an order of green algae in the class Ulvophyceae.
Bryopsis is a genus of marine green algae in the family Bryopsidaceae. It is frequently a pest in aquariums, where it is commonly referred to as hair algae.
Dangemannia is a genus of green algae in the family Oltmannsiellopsidaceae.
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 order 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.
eEF-1 are two eukaryotic elongation factors. It forms two complexes, the EF-Tu homolog EF-1A and the EF-Ts homolog EF-1B, the former's guanide exchange factor. Both are also found in archaea.
Chlorokybus is a multicellular (sarcinoid) genus of basal green algae or charophyte. It has been classified as the sole member of the family Chlorokybaceae, which is the sole member of the order Chlorokybales, in turn the sole member of the class Chlorokybophyceae. It grows on soil and rock surfaces, and is rare.
Coleochaetaceae is a family of algae. It is the only family in the Coleochaetales, an order of parenchymous charophyte algae, that includes some of the closest multicellular relatives of land plants. They questionably include the fossil genus Parka.
Chaetosphaeridiales is an order of green algae.
Palmophyllum is a genus of alga. This genus is known to grow in low light conditions and at depth. The known distribution of this genus is being extended as deeper waters are explored.
The Palmophyllophyceae are a proposed basal Chlorophyte clade consisting of the Palmophyllales and Prasinococcales.
The Phragmoplastophyta are a proposed sister clade of the Klebsormidiaceae in the Streptophyte/Charophyte clade. The Phragmoplastophyta consist of the Charophycaea and another unnamed clade which contains the Coleochaetophyceae, Zygnematophyceae, Mesotaeniaceae, and Embryophytes. It is an important step in the emergence of land plants within the green algae. It is equivalent to the ZCC clade/grade, cladistically granting the Embryophyta.
The Chlorophytina are a proposed basal Tetraphytina clade. It is currently seen as sister of the Pedinomonadaceae. It contains the more well-known green alga and is characterized by the presence of phycoplasts.
