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.
Volvox is a polyphyletic genus of chlorophyte green algae in the family Volvocaceae. Volvox species form spherical colonies of up to 50,000 cells, and for this reason they are sometimes called globe algae. They live in a variety of freshwater habitats, and were first reported by Antonie van Leeuwenhoek in 1700. Volvox diverged from unicellular ancestors approximately 200 million years ago.
The Volvocaceae are a family of unicellular or colonial biflagellates, including the typical genus Volvox. The family was named by Ehrenberg in 1834, and is known in older classifications as the Volvocidae. All species are colonial and inhabit freshwater environments.
Chlamydomonadales, also known as Volvocales, are an order of flagellated or pseudociliated green algae, specifically of the Chlorophyceae. Chlamydomonadales can form planar or spherical colonies. These vary from Gonium up to Volvox. Each cell has two flagella, and is similar in appearance to Chlamydomonas, with the flagella throughout the colony moving in coordination.
The green algae are a group of chlorophyll-containing autotrophic eukaryotes consisting of the phylum Prasinodermophyta and its unnamed sister group that contains the Chlorophyta and Charophyta/Streptophyta. The land plants (Embryophytes) have emerged deep in the Charophyte alga as a 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 (spherical), and filamentous forms, and macroscopic, multicellular seaweeds. There are about 22,000 species of green algae, many of which live most of their lives as single cells, while other species form coenobia (colonies), long filaments, or highly differentiated macroscopic seaweeds.
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 Sphaeropleales includes vegetatively non-motile unicellular, colonial, or filamentous taxa. They 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. Motile cells generally lack cell walls or have only a very fine layer surrounding the cell membrane. Other common characteristics include a robust vegetative cell wall, cup-shaped chloroplasts with large pyrenoids, and relatively large nuclei.
Gonium is a genus of colonial algae, a member of the order Chlamydomonadales. Typical colonies have 4 to 16 cells, all the same size, arranged in a flat plate, with no anterior-posterior differentiation. In a colony of 16 cells, four are in the center, and the other 12 are on the four sides, three each. A description by G.M. Smith :
Gonium Mueller 1773: Colonies of 4-8-16 cells arranged in a flat quadrangular plate and embedded in a common gelatinous matrix or connected by broad gelatinous strands. Cells ovoid to pyriform, with a single cup-shaped chloroplast containing one pyrenoid. Each cell with two cilia of equal length, contractile vacuoles at the base of the cilia, and an eyespot. Four- and eight-celled colonies with the cilia on the same side ; sixteen-celled colonies with the four central cells having their cilia on the same side and the twelve marginal cells with radially arranged cilia.
Asexual reproduction by simultaneous division of all cells in the colony to form autocolonies, or by a formation of 2-4 zoospores in each cell.
Sexual reproduction isogamous, by a fusion of biciliatezoogametes.
Chlamydomonadaceae is a family of algae within the order Chlamydomonadales. Traditionally, it has been defined as containing single-celled flagellates with a cell wall.
Selenastraceae is a family of green algae in the order Sphaeropleales. Members of this family are common components of the phytoplankton in freshwater habitats worldwide. A few species have been found in brackish and marine habitats, such as in the Baltic Sea.
Udoteaceae is a family of green algae, in the order Bryopsidales.
Astrephomene is a genus of green algae in the family Goniaceae, order Chlamydomonadales. The genus was first described in 1937 by Pocock and named by Pockock in 1953. The genome of Astrephomene gubernaculifera has been sequenced.
Eudorina is a paraphyletic genus in the volvocine green algae clade. Eudorina colonies consist of 16, 32 or 64 individual cells grouped together. Each individual cell contains flagella which allow the colony to move as a whole when the individual cells beat their flagella together. Description by GM Smith :
Pleodorina is a genus of colonial green algae in the family Volvocaceae. Description by Gilbert M. Smith.
Pleodorina Shaw 1894:
Colonies always motile; spherical to sub-spherical, with 32-128 cells lying some distance from one another just within the periphery of the homogeneous, hyaline, gelatinous, colonial envelope and not connected by cytoplasmic strands. Cells differentiated into those that are purely vegetative in character and those capable of dividing to form daughter colonies. All but four cells of the colony reproductive or about half reproductive and half vegetative. Cells spherical to ovoid in shape. Vegetative cells with a cup-shaped chloroplast containing one pyrenoid; a large anterior eyespot; two cilia of equal length with two contractile vacuoles at their base. Reproductive cells at first like the vegetative cells, later with a more massive chloroplast that eventually contains several pyrenoids. The eyespot and cilia of reproductive cells disappearing when they are mature.
Ankistrodesmus is a genus of green algae in the family Selenastraceae. It is one of the most common types of phytoplankton in freshwater habitats around the world.
Chloromonas is a genus of green algae in the family Chlamydomonadaceae. It is closely related to the model green algae, Chlamydomonas, and traditionally has been distinguished mainly through the absence of a pyrenoid.
Nephroselmis is a genus of green algae. It has been placed in the family Nephroselmidaceae, although a 2009 study suggests that it should be separated into its own class, Nephroselmidophyceae. One species can be an endosymbiont of Hatena arenicola.
Raphidocelis is a genus of green algae in the family Selenastraceae. They are found in freshwater habitats.
Selenastrum is a genus of green algae in the family Selenastraceae. It is common in freshwater habitats around the world. Most species prefer temperate or warm-temperate waters.
Trebouxia is a unicellular green alga. It is a photosynthetic organism that can exist in almost all habitats found in polar, tropical, and temperate regions. It can either exist in a symbiotic relationship with fungi in the form of lichen or it can survive independently as a free-living organism alone or in colonies. Trebouxia is the most common photobiont in extant lichens. It is a primary producer of marine, freshwater and terrestrial ecosystems. It uses carotenoids and chlorophyll a and b to harvest energy from the sun and provide nutrients to various animals and insects.
Asterochloris is a genus of green algae in the family Trebouxiophyceae. It is a common photobiont in lichen, occurring in the thalli of more than 20 lichen genera worldwide. Asterochloris is distinguishable from the morphologically similar genus Trebouxia, primarily due to its deeply lobed chloroplast, the placement of the chloroplast along the cell's periphery before the initiation of zoospore or aplanospore formation, and its tendency to primarily reproduce asexually through the production of aplanospores.
