Chlorophyta | |
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Chlorophytes (A–F, H–L and O) | |
Scientific classification | |
Domain: | Eukaryota |
Clade: | Diaphoretickes |
(unranked): | Archaeplastida |
(unranked): | Viridiplantae |
Division: | Chlorophyta Reichenbach, 1828, emend. Pascher, 1914, emend. Lewis & McCourt, 2004 [1] [2] [3] |
Classes [4] | |
Synonyms [5] | |
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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 the three classes Ulvophyceae, Trebouxiophyceae and Chlorophyceae in the UTC clade, 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 |
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green flagellate" |
A 2020 paper places the "Prasinodermophyta" (i.e. Prasinodermophyceae + Palmophyllophyceae) as the basal Viridiplantae clade. [26]
Viridiplantae/ |
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Green Algae/ Prasinophyta s.l. |
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]
The Chlorophyceae are one of the classes of green algae, distinguished mainly on the basis of ultrastructural morphology. They are usually green due to the dominance of pigments chlorophyll a and chlorophyll b. The chloroplast may be discoid, plate-like, reticulate, cup-shaped, spiral- or ribbon-shaped in different species. Most of the members have one or more storage bodies called pyrenoids located in the chloroplast. Pyrenoids contain protein besides starch. Some green algae may store food in the form of oil droplets. They usually have a cell wall made up of an inner layer of cellulose and outer layer of pectose.
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.
Charales is an order of freshwater green algae in the division Charophyta, class Charophyceae, commonly known as stoneworts. Depending on the treatment of the genus Nitellopsis, living (extant) species are placed into either one family (Characeae) or two. Further families are used for fossil members of the order. Linnaeus established the genus Chara in 1753.
The Embryophyta, or land plants, are the most familiar group of green plants that comprise vegetation on Earth. Embryophytes have a common ancestor with green algae, having emerged within the Phragmoplastophyta clade of green algae as sister of the Zygnematophyceae. The Embryophyta consist of the bryophytes plus the polysporangiophytes. Living embryophytes therefore include hornworts, liverworts, mosses, lycophytes, ferns, gymnosperms and flowering plants. The land plants have diplobiontic life cycles and it is accepted now that they emerged from freshwater, multi-celled algae.
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.
Sphaeropleales is an order of green algae that used to be called Chlorococcales. The order includes some of the most common freshwater planktonic algae such as Scenedesmus and Pediastrum. The Spaeropleales includes vegetatively non-motile unicellular or colonial taxa that have biflagellate zoospores with flagella that are directly opposed in direction : Sphaeroplea, Atractomorpha, Neochloris, Hydrodictyon, and Pediastrum. All of these taxa have basal body core connections.
Characeae is a family of freshwater green algae in the order Charales, commonly known as stoneworts. They are also known as brittleworts or skunkweed, from the fragility of their lime-encrusted stems, and from the foul odor these produce when stepped on.
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.
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 and Trochiliscales.
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.
Chlorococcales is a formerly recognized order of green algae in the class Chlorophyceae. As of February 2022, the type family Chlorococcaceae was placed in the order Chlamydomonadales.
Dictyochloris is a genus of green algae in the class Chlorophyceae. It is the sole genus of the family Dictyochloridaceae. It is commonly found in terrestrial and subaerial habitats.
The Pleurastrophyceae were a formerly recognized class of green algae, in the division Chlorophyta. It was created by Mattox and Stewart in 1984, containing four genera. More recent classifications tend to split the group. On the one hand, Tetraselmis seems to be a sister to the so-called UTC clade, thus making it part of the (paraphyletic) Prasinophyceae. The other three genera were Pleurastrum, Trebouxia, and Pseudotrebouxia, and most of the species which had been in those genera have been placed in the Trebouxiophyceae. However, Pleurastrum insigne, which had been specified as the type of Pleurastrophyceae, turns out to be part of the Chlorophyceae.
Mesostigma is a genus of unicellular biflagellate freshwater green algae, with a single species Mesostigma viride, covered by an outer layer of basket‐like scales instead of a cell wall. As of February 2022, AlgaeBase classified it as the only genus in the family Mesostigmataceae, the only family in the order Mesostigmatales, the only order in the class Mesostigmatophyceae. It is now considered to be one of the earliest diverging members of green plants/algae (Viridiplantae).
The following outline is provided as an overview of and topical guide to life forms:
A system of taxonomy of the cryptogams, the Smith system was published in:
The Hoek, Mann and Jahns system is a system of taxonomy of algae. It was first published in Algae: An Introduction to Phycology by Cambridge University Press in 1995.
Orciraptor is a genus of heterotrophic protists, containing the single species Orciraptor agilis. It belongs to the family Viridiraptoridae, in the phylum Cercozoa.