Chlorophyta



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 the three classes Ulvophyceae, Trebouxiophyceae and Chlorophyceae in the UTC clade, 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.

Ecology
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. 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. Some groups, such as the Trentepohliales are exclusively found on land. Several species of Chlorophyta live in symbiosis with a diverse range of eukaryotes, including fungi (to form lichens), ciliates, forams, cnidarians and molluscs. Some species of Chlorophyta are heterotrophic, either free-living or parasitic. Others are mixotrophic bacterivores through phagocytosis. Two common species of the heterotrophic green alga Prototheca are pathogenic and can cause the disease protothecosis in humans and animals.

Classifications


Characteristics used for the classification of Chlorophyta are: type of zoid, mitosis (karyokinesis), cytokinesis, organization level, life cycle, type of gametes, cell wall polysaccharides and more recently genetic data.

Phylogeny
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".

A 2020 paper places the "Prasinodermophyta" (i.e. Prasinodermophyceae + Palmophyllophyceae) as the basal Viridiplantae clade.

Leliaert et al. 2012
Simplified phylogeny of the Chlorophyta, according to Leliaert et al. 2012. Note that many algae previously classified in Chlorophyta are placed here in Streptophyta.
 * Viridiplantae
 * Chlorophyta
 * core chlorophytes
 * Ulvophyceae
 * Cladophorales
 * Dasycladales
 * Bryopsidales
 * Trentepohliales
 * Ulvales-Ulotrichales
 * Oltmannsiellopsidales
 * Chlorophyceae
 * Oedogoniales
 * Chaetophorales
 * Chaetopeltidales
 * Chlamydomonadales
 * Sphaeropleales
 * Trebouxiophyceae
 * Chlorellales
 * Oocystaceae
 * Microthamniales
 * Trebouxiales
 * Prasiola clade
 * Chlorodendrophyceae
 * prasinophytes (paraphyletic)
 * Pyramimonadales
 * Mamiellophyceae
 * Pycnococcaceae
 * Nephroselmidophyceae
 * Prasinococcales
 * Palmophyllales
 * Streptophyta
 * charophytes
 * Mesostigmatophyceae
 * Chlorokybophyceae
 * Klebsormidiophyceae
 * Charophyceae
 * Zygnematophyceae
 * Coleochaetophyceae
 * Embryophyta (land plants)

Pombert et al. 2005
A possible classification when Chlorophyta refers to one of the two clades of the Viridiplantae is shown below.
 * Class Prasinophyceae T. A. Chr. ex Ø. Moestrup & J. Throndsen
 * Class Chlorophyceae Wille
 * Class Trebouxiophyceae T. Friedl
 * Class Ulvophyceae

Lewis & McCourt 2004

 * Division Chlorophyta (green algae sensu stricto)
 * Subdivision Chlorophytina
 * Class Chlorophyceae (chlorophytes)
 * Order Chlamydomonadales (+ some Chlorococcales + some Tetrasporales + some Chlorosarcinales)
 * Order Sphaeropleales (sensu Deason, plus Bracteacoccus, Schroederia, Scenedesmaceae, Selanastraceae)
 * Order Oedogoniales
 * Order Chaetopeltidales
 * Order Chaetophorales
 * Incertae Sedis (Cylindrocapsa clade, Mychonastes clade)
 * Class Ulvophyceae (ulvophytes)
 * Order Ulotrichales
 * Order Ulvales
 * Order Siphoncladales/Cladophorales
 * Order Caulerpales
 * Order Dasycladales
 * Class Trebouxiophyceae (trebouxiophytes)
 * Order Trebouxiales
 * Order Microthamniales
 * Order Prasiolales
 * Order Chlorellales
 * Class Prasinophyceae (prasinophytes)
 * Order Pyramimonadales
 * Order Mamiellales
 * Order Pseudoscourfieldiales
 * Order Chlorodendrales
 * Incertae sedis (Unnamed clade of coccoid taxa)
 * Division Charophyta (charophyte algae and embryophytes)
 * Class Mesostigmatophyceae (mesostigmatophytes)
 * Class Chlorokybophyceae (chlorokybophytes)
 * Class Klebsormidiophyceae (klebsormidiophytes)
 * Class Zygnemophyceae (conjugates)
 * Order Zygnematales (filamentous conjugates and saccoderm desmids)
 * Order Desmidiales (placoderm desmids)
 * Class Coleochaetophyceae (coleochaetophytes)
 * Order Coleochaetales
 * Subdivision Streptophytina
 * Class Charophyceae (reverts to use of GM Smith)
 * Order Charales (charophytes sensu stricto)
 * Class Embryophyceae (embryophytes)

Hoek, Mann and Jahns 1995
Classification of the Chlorophyta, treated as all green algae, according to Hoek, Mann and Jahns 1995.
 * Class Prasinophyceae (orders Mamiellales, Pseudocourfeldiales, Pyramimonadales, Chlorodendrales)
 * Class Chlorophyceae (orders Volvocales [including the Tetrasporales], Chlorococcales, Chaetophorales, Oedogoniales)
 * Class Ulvophyceae (orders Codiolales, Ulvales)
 * Class Cladophorophyceae (order Cladophorales)
 * Class Bryopsidophyceae (orders Bryopsidales, Halimedales)
 * Class Dasycladophyceae (order Dasycladales)
 * Class Trentepohliophyceae (order Trentepohliales)
 * Class Pleurastrophyceae (order Pleurastrales)
 * Incertae sedis (order Prasiolales)
 * Class Klebsormidiophyceae (orders Klebsormidiales, Coleochaetales)
 * Class Zygnematophyceae (order Zygnematales, Desmidiales)
 * Class Charophyceae (order Charales)

In a note added in proof, an alternative classification is presented for the algae of the class Chlorophyceae:
 * Class Chlamydophyceae (orders Volvocales, Chlorococcales, Chaetophorales)
 * Class Oedogoniophyceae (order Oedogoniales)
 * Class Chlorophyceae (order Chlorellales)

Bold and Wynne 1985
Classification of the Chlorophyta and Charophyta according to Bold and Wynne 1985.


 * Chlorophyta, Chlorophyceae (16 orders)
 * Volvocales
 * Tetrasporales
 * Chlorococcales
 * Chlorosarcinales
 * Ulotrichales
 * Sphaeropleales
 * Chaetophorales
 * Trentepohliales
 * Oedogoniales
 * Ulvales
 * Cladophorales
 * Acrosiphoniales
 * Caulerpales
 * Siphonocladales
 * Dasycladales
 * Zygnematales
 * Charophyta, Charophyceae (1 order)
 * Charales

Mattox & Stewart 1984
Classification of the Chlorophyta according to Mattox & Stewart 1984:


 * Micromonadophyceae (similar to Prasinophyceae; Tetraselmidiales transferred to Pleurastrophyceae)
 * Charophyceae Rabenhorst
 * Chlorokybales
 * Klebsormidiales
 * Zygnematales
 * Coleochaetales
 * Charales
 * Ulvophyceae
 * Pleurastrophyceae
 * Tetraselmidiales
 * Pleurastrales
 * Chlorophyceae Wille in Warming
 * Chlamydomonadales
 * Volvocales
 * Chlorococcales
 * Sphaeropleales
 * Chlorosarcinales
 * Chaetophorales
 * Oedogoniales

Fott 1971
Classification of the Chlorophyta according to Fott 1971.
 * Class Chlorophyceae
 * Order Volvocales
 * Order Tetrasporales
 * Order Chlorococcales
 * Order Ulotrichales
 * Suborder Chlorosarcineae
 * Suborder Ulotrichineae
 * Suborder Oedogoniineae
 * Suborder Chaetophorineae
 * Order Siphonocladales
 * Order Bryopsidales


 * Class Conjugatophyceae
 * Class Charophyceae

Round 1971
Classification of the Chlorophyta and related algae according to Round 1971.


 * "green algae"
 * Euglenophyta
 * Prasinophyta
 * Charophyta
 * Chlorophyta
 * Zygnemaphyceae (= Conjugatophyceae; orders Mesotaeniales, Zygnematales, Gonatozygales, Desmidiales)
 * Oedogoniophyceae (order Oedogoniales)
 * Bryopsidophyceae
 * Hemisiphoniidae (orders Cladophorales, Sphaeropleales, Acrosiphoniales
 * Cystosiphoniidae (orders Dasycladales, Siphonocladales, Chlorochytriales)
 * Eusiphoniidae (orders Derbesiales, Codiales, Caulerpales, Dichotomosiphonales, Phyllosiphonales)
 * Chlorophyceae
 * orders Chlamydomonadales, Volvocales, Polyblepharidales, Tetrasporales, Chlorodendrales, Chlorosarcinales, Chlorococcales
 * orders Ulotrichales, Codiolales, Ulvales, Prasiolales, Cylindrocapsales, Microsporales
 * orders Chaetophorales, Coleochaetales, Trentepohliales, Pleurococcales, Ulvellales

Smith 1938
Classification of the Chlorophyta according to Smith 1938:


 * Class 1. Chlorophyceae
 * Order 1. Volvocales
 * Family 1. Chlamydomonadaceae
 * Family 2. Volvocaceae
 * Order 2. Tetrasporales
 * Order 3. Ulotrichales
 * Family 1. Ulotrichaceae
 * Family 2. Microsporaceae
 * Family 3. Cylindrocapsaceae
 * Family 4. Chaetophoraceae
 * Family 5. Protococcaceae
 * Family 6. Coleochaetaceae
 * Family 7. Trentepohliaceae
 * Order 4. Ulvales
 * Family 1. Ulvaceae
 * Family 2 Schizomeridaceae
 * Order 5. Schizogoniales
 * Family Schizogoniaceae
 * Order 6. Cladophorales
 * Family 1. Cladophoraceae
 * Family 2. Sphaeropleaceae
 * Order 7. Oedogoniales
 * Family Oedogoniaceae
 * Order 8. Zygnematales
 * Family 1. Zygnemataceae
 * Family 2. Mesotaeniaceae
 * Family 3. Desmidiaceae
 * Order 9. Chlorococcales
 * Family 1. Chlorococcaceae
 * Family 2. Endosphaeraceae
 * Family 3. Characiaceae
 * Family 4. Protosiphonaceae
 * Family 5. Hydrodictyaceae
 * Family 6. Oöcystaceae
 * Family 7. Scenedesmaceae
 * Order 10. Siphonales
 * Family 1. Bryopsidaceae
 * Family 2. Caulerpaceae
 * Family 3. Halicystaceae
 * Family 4. Codiaceae
 * Family 5. Derbesiaceae
 * Family 6. Vaucheriaceae
 * Family 7. Phyllosiphonaceae
 * Order 11. Siphonocladiales
 * Family 1. Valoniaceae
 * Family 2. Dasycladaceae


 * Class 2. Charophyceae
 * Order Charales
 * Family Characeae

Research and discoveries
In February 2020, the fossilized remains of green algae, named Proterocladus antiquus were discovered in the northern province of Liaoning, China. At around a billion years old, it is believed to be one of the oldest examples of a multicellular chlorophyte.