Cosmarium is a genus of freshwater organisms belonging to the Charophyta, a division of green algae from which the land plants (Embryophyta) emerged. [1] [2]
In this large genus the cells are very variable. All are constricted in the middle leading to its bi-lobed appearance; [3] the two halves are called semicells. Cells come in a variety of different shapes. The cell wall may be smooth or ornamented with spines, granules, scrobiculations (pits), or pores. Cells are generally flattened. [4] Cells usually have one or two chloroplasts filling the cell; each chloroplast contains pyrenoids, typically one or two. [5]
Species identification of Cosmarium depends on the shape of the cells and their ornamentation, and can be difficult. [4] In addition, the genera Actinotaenium and Euastrum can be similar to various species of Cosmarium. Actinotaenium is generally circular in cross section, and Euastrum usually (but not always) has a notch at the tip of each semicell. [4]
Cosmarium is the largest genus of desmids, with over 1,000 species. It is an artificial genus: the defining characteristics of the genus are vague and arbitrary, and there are some species that are intermediate between several different genera. It is also not monophyletic, as molecular phylogenetic studies have shown that the form of Cosmarium evolved independently many times over. Despite this, the genus is still in use, because there is no known way of classifying desmids in line with their evolutionary history. [6]
Cosmarium and other desmid genera tend to prefer oligotrophic, somewhat acidic water habitats, [4] but some species exist in more eutrophic and/or basic habitats. Some species, which are small and mostly plain, form a community known as a "Cosmarietum"; these may be further associated with a community of Closterium species forming a Cosmarietum-Closterietum association. [5]
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 refers to 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 refers to 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.
Chlamydomonas is a genus of green algae consisting of about 150 species of unicellular flagellates, found in stagnant water and on damp soil, in freshwater, seawater, and even in snow as "snow algae". Chlamydomonas is used as a model organism for molecular biology, especially studies of flagellar motility and chloroplast dynamics, biogenesis, and genetics. One of the many striking features of Chlamydomonas is that it contains ion channels (channelrhodopsins) that are directly activated by light. Some regulatory systems of Chlamydomonas are more complex than their homologs in Gymnosperms, with evolutionarily related regulatory proteins being larger and containing additional domains.
Desmidiales, commonly called the desmids, are an order in the Charophyta, a division of green algae in which the land plants (Embryophyta) emerged. Desmids consist of single-celled, microscopic green algae. Because desmids are highly symmetrical, attractive, and come in a diversity of forms, they are popular subjects for microscopists, both amateur and professional.
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.
Micrasterias is a unicellular green alga of the order Desmidiales. Its species vary in size reaching up to hundreds of microns.
Chlorodendrales are an order of green, flagellated, thecate, unicellular eukaryotes, within the green algae class Chlorodendrophyceae. Prasinophyceae are defined by their cellular scales which are composed of carbohydrates, and Chlorodendrales are unique within this group due to these scales forming a fused thecal wall. Cells of Chlorodendrales are completely covered in scales, which fuse around the cell body producing the theca, but remain individually separated on the flagella, of which there are typically four per cell. Species within Chlorodendrales live in both marine and fresh water habitats, occupying both benthic and planktonic food webs. Additionally, they are photoautotrophs, meaning they produce their own food through the conversion of sunlight into chemical energy.
Lagerheimia is a genus of green algae in the family Oocystaceae. It is commonly found in freshwater habitats all over the world, although some species are rare and have only been recorded from Europe or the United States.
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.
The Desmidiaceae are one of four families of charophyte green algae in the order Desmidiales (desmids).
Desmidium is a genus of green algae, specifically of the Desmidiaceae.
Euastrum is a genus of green algae of the Desmidiaceae family. It lives in acidic waters.
Pleurotaenium is a genus of green algae, specifically of the desmids (Desmidiaceae).
Triploceras is a genus of desmid in the family Desmidiaceae.
Xanthidium is a genus of green algae, specifically of the Desmidiaceae.
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.
Mesostigma is a genus of freshwater green algae, with a single species Mesostigma viride. 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).
Zygnematophyceae is a class of green algae in the paraphylum streptophyte algae, also referred to as Charophyta, consisting of more than 4000 described species. It contains five orders: the Spirogloeales, the Serritaeniales, the Zygnematales, the Spirogyrales, and the Desmidiales. The Zygnematophyceae are the sister clade of the land plants. The body plan of Zygnematophyceae is simple, and appear to have gone through a secondary loss of morphological complexity. The most basal members are unicellular, but filamentous species have evolved at least five times. They contain genes involved in protection from desiccation that appear to have been derived by horizontal gene transfer from bacteria; the genes are found in plants, Zygnematophyceae, bacteria, but no other organisms. The genes may have helped to enable plants to make the transition to life on land.
The Mesotaeniaceae are a small family of unicellular green algae known as the "saccoderm desmids". The Mesotaeniaceae appear to be sister or ancestral to the Zygnemataceae. The desmids are a deep branching group of Zygnemataceae. Spirotaenia was found to be a basal green alga.
Cosmarium tetragonum is a species of green algae in the family Desmidiaceae. It is a freshwater species with a worldwide distribution.
Prescottiella is a genus of green algae in the family Desmidiaceae, containing the single species Prescottiella sudanensis. Originally classified as Micrasterias sudanensis in 1958, it was moved into its own genus by Carlos E. M. Bicudo in 1976, due to its asymmetric character. It is named after Gerald Webber Prescott, an American phycologist.
