''Tetrastrum'' 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 ...

(Chlorophyta). It is a common component of the

phytoplankton Phytoplankton () are the autotrophic (self-feeding) components of the plankton community and a key part of ocean and freshwater Aquatic ecosystem, ecosystems. The name comes from the Greek language, Greek words (), meaning 'plant', and (), mea ...

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 ...

habitats, particularly

eutrophic Eutrophication is a general term describing a process in which nutrients accumulate in a body of water, resulting in an increased growth of organisms that may deplete the oxygen in the water; ie. the process of too many plants growing on the s ...

and alkaline waters. Although traditionally classified in the family

Scenedesmaceae Scenedesmaceae is a family of green algae in the order Sphaeropleales. ''Scenedesmus'' algae are commonly found in freshwater plankton. The former family Coelastraceae is considered a synonym of Scenedesmaceae. The family has existed since at ...

in the class Chlorophyceae, it is

phylogenetically In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical data ...

more closely related to the genus ''

Oocystis ''Oocystis'' is a planktonic genus of mostly freshwater green algae of the Family (biology), family Oocystaceae. It is the type genus of its family. ''Oocystis'' is mostly found in freshwater habitats and has a cosmopolitan distribution. A few sp ...

'' of the family

Oocystaceae Oocystaceae is a family (biology), family of green algae, in the class Trebouxiophyceae. Molecular phylogenetic studies mostly (but not always) place the family in the order Chlorellales, as sister to Chlorellaceae. The Type (biology), type genus ...

(

Trebouxiophyceae The Trebouxiophyceae, also known as trebouxiophytes, are a class of green algae, in the division Chlorophyta. Members of this class are single-celled, colonial, or multicellular and are found in freshwater, terrestrial or marine habitats worldwid ...

History

The genus ''Tetrastrum'' has a tangled taxonomic history. The name was first coined in 1895 by

Robert Chodat Robert Hippolyte Chodat (4 June 1865, Moutier – 28 April 1934) was a Swiss botanist and phycologist who was a professor and director of the botanical institute at the University of Geneva. He studied medicine and botany at Geneva, where he was ...

for the species '' Tetrastrum heteracanthum'', which was previously placed in the now-obsolete genus ''Staurogenia''. Later, the genus ''Cohniella'' was created by Ludwig Julius Bruno Schröder, containing the species ''Cohniella staurogeniiforme''. Later,

Ernst Lemmermann Ernst Johann Lemmermann (27 May 1867 in Bremen – 11 May 1915 in Bremen) was a German botanist who specialized in the field of phycology. During his career he taught classes (''Seminarlehrer'') in Bremen, where he also worked as a botanical ...

merged the genus ''Cohniella'' into ''Tetrastrum''.

Description

''Tetrastrum'' consists of four-celled colonies, which are sometimes aggregated together to form compound colonies. A layer of

mucilage Mucilage is a thick gluey substance produced by nearly all plants and some microorganisms. These microorganisms include protists which use it for their locomotion, with the direction of their movement always opposite to that of the secretion of ...

surrounding the colony is sometimes present. Cells are tightly joined in a flat plane, with or without a small space in the middle. Cells are ovoid, triangular, or trapezoidal, 2–11.5 μm long. Some species may have spines on the cells; these spines are up to 46 μm and show various morphologies, such as one long spine and one short, or multiple short spines. Cells contain one

nucleus Nucleus (: nuclei) is a Latin word for the seed inside a fruit. It most often refers to: *Atomic nucleus, the very dense central region of an atom *Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA Nucleu ...

and one to four

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 ...

s, with or without

pyrenoid Pyrenoids are sub-cellular phase-separated micro-compartments found in chloroplasts of many algae,Giordano, M., Beardall, J., & Raven, J. A. (2005). CO2 concentrating mechanisms in algae: mechanisms, environmental modulation, and evolution. ''An ...

s. The cell wall appears smooth in

light microscopy Microscopy is the technical field of using microscopes to view subjects too small to be seen with the naked eye (objects that are not within the resolution range of the normal eye). There are three well-known branches of microscopy: optical, el ...

, but is covered with small granules which are visible in

scanning electron microscopy A scanning electron microscope (SEM) is a type of electron microscope that produces images of a sample by scanning the surface with a focused beam of electrons. The electrons interact with atoms in the sample, producing various signals that ...

. ''Tetrastrum'' reproduces asexually through the formation of

autospore Autospores are a type of spores that are produced by algae to enable asexual reproduction and spread. They are non-motile and non-Flagellated cell, flagellated Aplanospore, aplanospores that are generated within a parent cell and have the same sha ...

s. Four autospores are formed, organized into the shape of the colony; these are released through a tear in the mother cell wall.

Identification

''Tetrastrum'' is similar to, and has been taxonomically confused with, other genera such as '' Crucigenia''. The main morphological difference between the two is the mode of

reproduction Reproduction (or procreation or breeding) is the biological process by which new individual organisms – "offspring" – are produced from their "parent" or parents. There are two forms of reproduction: Asexual reproduction, asexual and Sexual ...

. In ''Tetrastrum'', the daughter colonies are produced with the cells in the same orientation as the mother cells. In ''Crucigenia'', the daughter colonies are produced with cells rotated 45° relative to the mother cells' orientation. Additionally, ''Tetrastrum'' may produce spines on its cells, while ''Crucigenia'' never does. Some species once classified in the genus ''Tetrastrum'' have been reclassified into the genus ''

Lemmermannia ''Lemmermannia'' Help:IPA, /ˌlɛməɹˈmæniə/ is a genus of fresh water Trebouxiophyceae, trebouxiophyceans. , the genus contains five described species. They form coenocyte, coenobia of 4 to 16 cells. Bock, C., Luo, W., Kusber, W.-H., Hegewal ...

''. ''Lemmermannia'' has square colonies that lack spines, and can sometimes form compound colonies; in contrast, ''Tetrastrum'' has colonies with spines, or in the case of the spineless '' Tetrastrum glabrum'', has oval and not square colonies). Species of ''Tetrastrum'' are identified based on the size and shape of the cells, placement and length of the spines, and presence or absence of pyrenoids. Considerable variation exists within species, blurring species boundaries.

References

* * {{Taxonbar, from=Q7706754 Sphaeropleales genera Sphaeropleales Freshwater algae