The Zygnemataceae are a family of filamentous or

unicellular A unicellular organism, also known as a single-celled organism, is an organism that consists of a single cell, unlike a multicellular organism that consists of multiple cells. Organisms fall into two general categories: prokaryotic organisms and ...

, uniseriate (unbranched)

green alga The green algae (singular: green alga) are a group consisting of the Prasinodermophyta and its unnamed sister which contains the Chlorophyta and Charophyta/Streptophyta. The land plants (Embryophytes) have emerged deep in the Charophyte alga as ...

e. The filaments are septated and reproduction is by

conjugation Conjugation or conjugate may refer to: Linguistics * Grammatical conjugation, the modification of a verb from its basic form * Emotive conjugation or Russell's conjugation, the use of loaded language Mathematics * Complex conjugation, the chang ...

; ''

Spirogyra ''Spirogyra'' (common names include water silk, mermaid's tresses, and blanket weed) is a genus of filamentous charophyte green algae of the order Zygnematales, named for the helical or spiral arrangement of the chloroplasts that is characteris ...

'' is commonly used in schools to demonstrate this kind of reproduction. The family is notable for its diversely shaped

chloroplast A chloroplast () is a type of membrane-bound organelle known as a plastid that conducts photosynthesis mostly in plant and algal cells. The photosynthetic pigment chlorophyll captures the energy from sunlight, converts it, and stores it in ...

s, such as stellate in ''

Zygnema ''Zygnema'' is a genus of freshwater filamentous thalloid alga Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multi ...

'',

helical Helical may refer to: * Helix, the mathematical concept for the shape * Helical engine, a proposed spacecraft propulsion drive * Helical spring, a coilspring * Helical plc, a British property company, once a maker of steel bar stock * Helicoil A t ...

in ''

'', 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, 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.Wehr, John D. and Sheath, Robert G. ''Freshwater Algae of North America'', pg. 363. While they occupy many habitats, in North America all are found solely in freshwater or

subaerial In natural science, subaerial (literally "under the air"), has been used since 1833,Subaerial
in the Merriam ...

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

chytrid Chytridiomycota are a division of zoosporic organisms in the kingdom Fungi, informally known as chytrids. The name is derived from the Ancient Greek ('), meaning "little pot", describing the structure containing unreleased zoöspores. Chytrid ...

s. Most genera (all except ''Mesotanium'' and ''Spirotaenia'') previously assigned to

Mesotaeniaceae The Mesotaeniaceae are a small family of unicellular green algae known as the "saccoderm desmids". The Mesotaeniaceae appear to be sister or ancestral to the Zygnemataceae. The desmids are a deep branching group of Zygnemataceae. ''Spirotaenia' ...

as well as the

Desmidiales Desmidiales, commonly called desmids (''Gr.'' ''desmos'', bond or chain), are an order in the Charophyta, a division of green algae in which the land plants (Embryophyta) emerged. Or in other words, Desmid, (order Desmidiales), order of single ...

actually emerged in the Zygnematacae.

References

Zygnematophyceae families {{green algae-stub