Mougeotia
Scientific classification
Clade:	Viridiplantae
(unranked):	Charophyta
Class:	Zygnematophyceae
Order:	Zygnematales
Family:	Zygnemataceae
Genus:	Mougeotia C.Agardh, 1824
Type species
Mougeotia genuflexa (Roth) C.Agardh, 1824[1]
Species
See text.

Mougeotia is a genus of filamentous charophyte green algae of the order Zygnematales. It is a common component of freshwater aquatic habitats around the world.^[2] Described in 1824 by Carl Adolph Agardh,^[1] its name honors the French botanist Jean-Baptiste Mougeot.^[3]

Mougeotia forms uniserial (one cell thick) chains of cells, called filaments, that are usually unbranched; in certain conditions, it forms branched filaments. Cells are cylindrical, many times longer than wide. Each cell has one or two flat, rectangular and ribbon-shaped chloroplasts that fill the cell. Chloroplasts are able to twist in response to light conditions.^[2] The nucleus is located at the center of the cell.^[3]

Mougeotia is able to reproduce sexually, through a process known as conjugation. It is isogamous, with two different but identically appearing gamete types.^[4]

In scalariform conjugation, cells of two separate filaments line up parallel to one other. Cells of one filament connect to those of the other via a tube.^[5]

In its vegetative state, Mougeotia appears essentially identical to two other genera, Transeauina and Temnogametum. Transeauina (formerly known as Debarya) is distinguished from Mougeotia in having gametangia filled with layers of pectin giving it a stratified appearance. Temnogametum is a rare genus that is probably restricted to the tropics; it differs from Mougeotia in having spores filled with oil droplets. Mougeotia is also similar to the genus Mougeotiopsis, but the latter genus has chloroplasts that lack pyrenoids.^[2]

Species identification depends on observing the morphology of reproductive structures, called zygospores; this is difficult because they are rarely present.^[6]

Mougeotia and the related genus Mesotaenium display chloroplast movement in response to light. When exposed to red light or low levels of white light, the chloroplast twists along its long axis until it is perpendicular to the direction of the light, thus achieving maximum irradiation. When exposed to blue and white light at the same time (such as in high levels of white light), the chloroplast rotates to minimize irradiation.^[7]

Chloroplast rotation is mediated by phytochrome molecules located at the plasma membrane, as well as an additional pigment that absorbs blue light. When absorbing light, the pigment forms a gradient along the plasma membrane, which is then transduced into a movement response. Although the exact mechanism behind the gradient is unknown, it is known that the chloroplast is moved by F-actin threads attached to the membrane.^[7]

Mougeotia prefers meso-oligotrophic, especially acidic freshwater habitats^[3] and can form algal blooms. Its growth is not optimal under acidic conditions, but Mougeotia can tolerate the heavy metals such as aluminum and zinc that are more biologically available, and is efficient at gathering dissolved inorganic carbon.^[3]

Several characteristics of Mougeotia appear to contribute to ability to form blooms. In conditions of where phosphorus is the limiting nutrient, Mougeotia is able to compete well, and its chloroplast can rotate allowing it to persist in lower-light conditions. Its filamentous morphology allows Mougeotia to slow down the rate of sinking. Although Mougeotia is not known to be toxic, it is mostly inedible for zooplankton.^[6] In Israel, it has become an invasive species.^[8]

As of May 2023^[update], AlgaeBase accepted the following species:^[1]

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