Cosmarium is a large genus of desmids (Desmidiaceae), a group of green algae closely related to the land plants (Embryophyta). [1] [2] Members of this genus are microscopic and found in freshwater habitats around the world. [3]
The name Cosmarium comes from the Greek word κοσμάριον - kosmarion, meaning a small ornament. [4]
Cosmarium, with few exceptions, consists of single cells and is thus microscopic. Cells are constricted in the middle, giving them a bilobed appearance; [5] 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. [6] Cells usually have one or two chloroplasts filling the cell; each chloroplast contains pyrenoids, typically one or two. [3]
Species identification of Cosmarium depends on the shape of the cells and their ornamentation, and can be difficult. [6] 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. [6]
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. [7]
Cosmarium and other desmid genera tend to prefer oligotrophic, somewhat acidic water habitats, [6] 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. [3]
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.
Micrasterias is a unicellular green alga of the order Desmidiales. Its species vary in size reaching up to hundreds of microns.
Carteria is a genus of green algae in the family Chlamydomonadaceae. Carteria are similar in morphology to the common genus Chlamydomonas and differ by having four, rather than two, flagella at the vegetative stage.
Lobomonas is a genus of green algae in the family Chlamydomonadaceae, found in freshwater habitats. Although it is widely distributed, it is a rare genus.
Sphaeroplea is a genus of green algae in the family Sphaeropleaceae. It was first circumscribed by the Swedish botanist Carl Adolph Agardh in 1824.
Stauridium is a genus of green algae in the family Hydrodictyaceae. It is very common in freshwater regions throughout the world.
Treubaria is a genus of microscopic green algae, the sole genus in the family Treubariaceae. Treubaria is found in freshwater habitats and has a cosmopolitan distribution.
Vitreochlamys is a genus of green algae in the family Chlamydomonadaceae. It is sometimes known by the name Sphaerellopsis, published by Aleksandr Arkadievich Korshikov. However, that name is an illegitimate later homonym, preceded by SphaerellopsisM.C.Cooke. It is commonly found in freshwater habitats.
The Desmidiaceae are one of four families of charophyte green algae in the order Desmidiales (desmids).
Closterium is a genus of desmid, a group of charophyte green algae. It is placed in the family Closteriaceae. Species of Closterium are a common component of freshwater microalgae flora worldwide.
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).
Spinoclosterium is a genus of green algae, specifically of the Closteriaceae. It is rare, but widely distributed in freshwater regions throughout the world.
Staurastrum is a large genus of desmids (Desmidiaceae), a group of green algae closely related to the land plants (Embryophyta). Members of this genus are microscopic and found in freshwater habitats around the world.
Staurodesmus is a genus of green algae, specifically of the Desmidiaceae.
Triploceras is a genus of desmid in the family Desmidiaceae.
Xanthidium is a genus of green algae, specifically of the Desmidiaceae.
Zygnematophyceae is a class of green algae in the paraphylum streptophyte algae, also referred to as Charophyta, consisting of more than 4000 described species. The Zygnematophyceae are the sister clade of the Embryophyta.
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.
