Chlorophyta is a taxon of green algae informally called chlorophytes.[6] 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[7][8] 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 (land plants) emerged.[9][10] In this latter sense the Chlorophyta includes only about 4,300 species.[4] About 90% of all known species live in freshwater.[11] Like the land plants (embryophytes: bryophytes and tracheophytes), green algae (chlorophytes and charophytes besides embryophytes) contain chlorophyll a and chlorophyll b and store food as starch[7] in their plastids.
With the exception of Palmophyllophyceae, Trebouxiophyceae, Ulvophyceae and Chlorophyceae, which show various degrees of multicellularity, all the Chlorophyta lineages are unicellular.[12] Some members of the group form symbiotic relationships with protozoa, sponges, and cnidarians. Others form symbiotic relationships with fungi to form lichens, but the majority of species are free-living. Some conduct sexual reproduction, which is oogamous or isogamous. All members of the clade have motile flagellated swimming cells.[13] While most species live in freshwater habitats and a large number in marine habitats, other species are adapted to a wide range of land environments. For example, Chlamydomonas nivalis, which causes Watermelon snow, lives on summer alpine snowfields. Others, such as Trentepohlia species, live attached to rocks or woody parts of trees. Monostroma kuroshiense, an edible green alga cultivated worldwide and most expensive among green algae, belongs to this group.
Species of Chlorophyta (treated as what is now considered one of the two main clades of Viridiplantae) are common inhabitants of marine, freshwater and terrestrial environments.[14][15] Several species have adapted to specialised and extreme environments, such as deserts, arctic environments, hypersaline habitats, marine deep waters, deep-sea hydrothermal vents and habitats that experiences extreme changes in temperature, light and salinity.[16][17][18][19] Some groups, such as the Trentepohliales are exclusively found on land.[20] Several species of Chlorophyta live in symbiosis with a diverse range of eukaryotes, including fungi (to form lichens), ciliates, forams, cnidarians and molluscs. [15] Some species of Chlorophyta are heterotrophic, either free-living or parasitic.[21][22] Others are mixotrophic bacterivores through phagocytosis.[23] Two common species of the heterotrophic green alga Prototheca are pathogenic and can cause the disease protothecosis in humans and animals.[24]
Characteristics used for the classification of Chlorophyta are: type of zoid, mitosis (karyokinesis), cytokinesis, organization level, life cycle, type of gametes, cell wall polysaccharides[25] and more recently genetic data.
Leliaert et al. 2012 proposed the following phylogeny. He marked the "prasinophytes" as paraphyletic, with the remaining Chlorophyta groups as "core chlorophytes". He described all Streptophyta except the land plants as paraphyletic "charophytes".[15]
"Hypothetical ancestral Chlorophyta StreptophytaCharophyceae (stoneworts)
Embryophyte (Land plants)
green flagellate"A 2020 paper places the "Prasinodermophyta" (i.e. Prasinodermophyceae + Palmophyllophyceae) as the basal Viridiplantae clade.[26]
Viridiplantae/ Prasinodermophyta PalmophyllophyceaePrasinococcales ("prasinophyte clade VI")
ChlorophytaPyramimonadophyceae ("prasinophyte clade I")
Mamiellophyceae ("prasinophyte clade II")
Nephroselmidophyceae ("prasinophyte clade III")
Pycnococcaceae ("prasinophyte clade V")
Chloropicophyceae ("prasinophyte clade VII A/B/C")
TetraphytinaChlorodendrophyceae ("prasinophyte clade IV")
Streptophyta/ Mesostigmatophyceae PhragmoplastophytaCharophyceae (stoneworts)
Coleochaetophyceae ZygnematophyceaeEmbryophyte (Land plants)
Charophyta Green Algae/Simplified phylogeny of the Chlorophyta, according to Leliaert et al. 2012.[15] Note that many algae previously classified in Chlorophyta are placed here in Streptophyta.
A possible classification when Chlorophyta refers to one of the two clades of the Viridiplantae is shown below.[27]
Classification of the Chlorophyta, treated as all green algae, according to Hoek, Mann and Jahns 1995.[7]
In a note added in proof, an alternative classification is presented for the algae of the class Chlorophyceae:
Classification of the Chlorophyta and Charophyta according to Bold and Wynne 1985.[29]
Classification of the Chlorophyta according to Mattox & Stewart 1984:[28]
Classification of the Chlorophyta according to Fott 1971.[7]: 483
Classification of the Chlorophyta and related algae according to Round 1971.[30]
Classification of the Chlorophyta according to Smith 1938:
In February 2020, the fossilized remains of green algae, named Proterocladus antiquus were discovered in the northern province of Liaoning, China.[31] At around a billion years old, it is believed to be one of the oldest examples of a multicellular chlorophyte.[32]
Green algae on coastal rocks at Shihtiping in Taiwan 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 (land plants) 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 (embryophytes: bryophytes and tracheophytes), green algae (chlorophytes and charophytes besides embryophytes) contain chlorophyll a and chlorophyll b and store food as starch in their plastids.
With the exception of Palmophyllophyceae, Trebouxiophyceae, Ulvophyceae and Chlorophyceae, which show various degrees of multicellularity, all the Chlorophyta lineages are unicellular. Some members of the group form symbiotic relationships with protozoa, sponges, and cnidarians. Others form symbiotic relationships with fungi to form lichens, but the majority of species are free-living. Some conduct sexual reproduction, which is oogamous or isogamous. All members of the clade have motile flagellated swimming cells. While most species live in freshwater habitats and a large number in marine habitats, other species are adapted to a wide range of land environments. For example, Chlamydomonas nivalis, which causes Watermelon snow, lives on summer alpine snowfields. Others, such as Trentepohlia species, live attached to rocks or woody parts of trees. Monostroma kuroshiense, an edible green alga cultivated worldwide and most expensive among green algae, belongs to this group.
