Zygnemataceae

The Zygnemataceae are a family of filamentous or unicellular, uniseriate (unbranched) green algae. The filaments are septated and reproduction is by conjugation; Spirogyra is commonly used in schools to demonstrate this kind of reproduction. The family is notable for its diversely shaped chloroplasts, such as stellate in Zygnema, helical in Spirogyra, and flat in Mougeotia. The Zygnemataceae are cosmopolitan, but though all generally occur in the same types of habitats, Mougeotia, Spirogyra, and Zygnema are by far the most common; in one study across North America,[2] 95% of the Zygnemataceae collected were in these three genera. Classification and identification is primarily by the morphology of the conjugation, which is somewhat rare to find in natural populations of permanent water bodies; when in the vegetative state, the rarer genera resemble the three most common, and are often mistaken for them and catalogued as such. Conjugation can be induced in low-nitrogen culture.[3] While they occupy many habitats, in North America all are found solely in freshwater or subaerial habitats. Species typically exist as floating mats in stagnant water in ditches and ponds, but some also grow in moving water, attaching themselves to a substrate by rhizoid-like projections of the basal cells of the filament. The mat species rise to the surface in early spring, grow rapidly through the summer, disappearing by late summer. Members of the Zygnemataceae, such as Spirogyra, fall prey to parasites, especially chytrids.[3] Most genera (all except Mesotanium and Spirotaenia) previously assigned to Mesotaeniaceae as well as the Desmidiales actually emerged in the Zygnematacae.[4]

Zygnemataceae
Spirogyra sp.
Scientific classification
(unranked):	Viridiplantae
Class:	Zygnematophyceae
Order:	Zygnematales
Family:	Zygnemataceae Kützing, 1843
Subgroups
Desmidiales †Cycloovoidites Krutzsch & Pacltová, 1990 Ghosella Randhawa, 1934 Lloydina A.Ahmad & M.Goldstein, 1972 Mougeotia C.Agardh, 1824 Mougeotiella Yamagishi, 1963 Mougeotiopsis Palla, 1894 Neozygnema Yamagishi, 1963 †Ovoidites Potonié, 1966 Sangirellum A.K.Mahato & P.Mahato, 1994 Sirocladium Randhawa, 1941 Sirogonium Kützing, 1843 Spirogyra Link, 1820 †Stigmozygodites Krutzsch & Pacltová, 1990 Temnogametum West & G.S.West, 1897 Temnogyra I.F.Lewis, 1925 Transeauina Guiry, 2013 Trigonum A.K.Mahato & P.Mahato, 1994 Zygnema C.Agardh, 1817 Zygnemopsis (Skuja) Transeau, 1934 Zygogonium Kützing, 1843 Ancylonema Berggren, 1872 Cylindrocystis Meneghini ex De Bary, 1858 Geniculus Prescott, 1967 Netrium (Nägeli) Itzigsohn & Rothe, 1856 Nucleotaenium Gontcharov & Melkonian, 2010 Planotaenium (Ohtani) Petlovany & Palamar-Mordvintseva, 2009 Roya West & G.S.West, 1896 Tortitaenia A.J.Brook, 1998
Synonyms[1]
Zygnemeae Kützing, 1843

References

Spirogyra mats in a still pond.

1. Guiry, M.D. (2013). Taxonomy and nomenclature of the Conjugatophyceae (=Zygnematophyceae). Algae. An International Journal of Algal Research 28: 1-29.
2. McCourt et al., 1986, as reported in Wehr, 2003, pg. 363
3. Wehr, John D. and Sheath, Robert G. Freshwater Algae of North America, pg. 363.
4. Gitzendanner, Matthew A.; Soltis, Pamela S.; Wong, Gane K.-S.; Ruhfel, Brad R.; Soltis, Douglas E. (2018). "Plastid phylogenomic analysis of green plants: A billion years of evolutionary history". American Journal of Botany. 105 (3): 291–301. doi:10.1002/ajb2.1048. ISSN 0002-9122. PMID 29603143.