''Actinotaenium'' is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

green algae The green algae (: green alga) 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 ...

, specifically of the

Desmidiaceae The Desmidiaceae are one of four family (biology), families of Charophyta, charophyte green algae in the order (biology), order Desmidiales (desmids).See the National Center for Biotechnology Information, NCBI]webpage on Desmidiaceae Data extrac ...

. It is a

freshwater Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. The term excludes seawater and brackish water, but it does include non-salty mi ...

genus, typically found in the

benthos Benthos (), also known as benthon, is the community of organisms that live on, in, or near the bottom of a sea, river, lake, or stream, also known as the benthic zone.oligotrophic An oligotroph is an organism that can live in an environment that offers very low levels of nutrients. They may be contrasted with copiotrophs, which prefer nutritionally rich environments. Oligotrophs are characterized by slow growth, low rates o ...

lakes or ''

Sphagnum ''Sphagnum'' is a genus of approximately 380 accepted species of mosses, commonly known as sphagnum moss, also bog moss and quacker moss (although that term is also sometimes used for peat). Accumulations of ''Sphagnum'' can store water, since ...

'' bogs. It has a

cosmopolitan distribution In biogeography, a cosmopolitan distribution is the range of a taxon that extends across most or all of the surface of the Earth, in appropriate habitats; most cosmopolitan species are known to be highly adaptable to a range of climatic and en ...

. ''Actinotaenium'' consists of solitary cells with two halves, called semicells; cells have a central constriction called an isthmus where the two semicells are joined. Cells are globose, ovoid, cylindrical or pyramidal when viewed from the side, but circular when viewed from the poles. The

cell wall A cell wall is a structural layer that surrounds some Cell type, cell types, found immediately outside the cell membrane. It can be tough, flexible, and sometimes rigid. Primarily, it provides the cell with structural support, shape, protection, ...

s are covered in ornamentation such as fine pores, punctae or scrobiculae (pits); the distribution of ornamentation varies by species. Each semicell has a single

chloroplast A chloroplast () is a type of membrane-bound organelle, organelle known as a plastid that conducts photosynthesis mostly in plant cell, plant and algae, algal cells. Chloroplasts have a high concentration of chlorophyll pigments which captur ...

, which is stellate in cross-section and often with complex lobes.

Asexual reproduction Asexual reproduction is a type of reproduction that does not involve the fusion of gametes or change in the number of chromosomes. The offspring that arise by asexual reproduction from either unicellular or multicellular organisms inherit the f ...

occurs by vegetative cell division, similar to that of ''

Cosmarium ''Cosmarium'' 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. The name ''Cosmarium'' co ...

''. Sexual reproduction is by conjugation, with zygotes forming between cells. Mature zygospores are quadrate, or globose with smooth walls, protuberances or spines.

Taxonomic history

In 1849,

Carl Nägeli Carl Wilhelm von Nägeli (26 or 27 March 1817 – 10 May 1891) was a Swiss botanist. He studied cell division and pollination but became known as the man who discouraged Gregor Mendel from further work on genetics. He rejected natural selecti ...

proposed the genus '' Dysphinctium'' for elongate desmids with circular or oval vertical view. Within ''Dysphinctium'' he named three

subgenera In biology, a subgenus ( subgenera) is a taxonomic rank directly below genus. In the International Code of Zoological Nomenclature, a subgeneric name can be used independently or included in a species name, in parentheses, placed between the ge ...

: ''Actinotaenium'', ''Calocylindrus'' and ''Dysphinctium''. These subgenera were largely not used by later taxonomists, and were instead placed in various genera including ''

Cylindrocystis ''Cylindrocystis'' is a genus of algae belonging to the family Mesotaeniaceae. The species of this genus are found in Europe and America. Species: *''Cylindrocystis angulatum'' *''Cylindrocystis cylindrospora'' *''Cylindrocystis diplospora'' ...

'', ''

'', and '' Penium''. By the twentieth century, the genus ''Cosmarium'' was recognized as an unwieldly, heterogeneous assemblage of species; it was a

wastebasket taxon Wastebasket taxon (also called a wastebin taxon, dustbin taxon or catch-all taxon) is a term used by some taxonomists to refer to a taxon that has the purpose of classifying organisms that do not fit anywhere else. They are typically defined by e ...

, defined mostly by a lack of features in other genera. To partially remedy this, in 1954 the desmid taxonomist Einar Teiling split off species that are elongate, circular in apical view, and with a minimal constriction at the middle. In contrast, ''Cosmarium'' has since been defined to include species that are compressed in vertical view. Although widely, Teiling's contributions did not strictly adhere to the

International Code of Botanical Nomenclature The ''International Code of Nomenclature for algae, fungi, and plants'' (ICN or ICNafp) is the set of rules and recommendations dealing with the formal botanical names that are given to plants, fungi and a few other groups of organisms, all tho ...

and this was fixed by J. Růžička & Z. Pouzar in 1978. Although Teiling considered ''Actinotaenium'' to be a natural and "primitive" genus, the genus is known to be

polyphyletic A polyphyletic group is an assemblage that includes organisms with mixed evolutionary origin but does not include their most recent common ancestor. The term is often applied to groups that share similar features known as Homoplasy, homoplasies ...

according to molecular phylogenetic studies.

References

External links

AlgaTerra database

Index Nominum Genericorum
{{Taxonbar, from=Q343467 Desmidiaceae Charophyta genera