Zygnematales

The Zygnematales ( (zygós) and νῆμα (nḗma) (nom.), νήματος (nḗmatos) (gen.)), also called the Conjugatales, are an order of green algae, comprising several thousand different species in two families. The larger family Zygnemataceae, with well-known genera such as Zygnema and Spirogyra, includes members that grow as unbranched filaments, which grow longer through normal cell division. This group includes the desmids. Most members of both families live in freshwater, and form an important component of the algal scum that grows on or near plants and rocks.

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 was found to be a basal green alga.

Netrium is a genus of algae belonging to the family Mesotaeniaceae.

Mesotaenium is a genus of algae belonging to the family Mesotaeniaceae.

Ancylonema is a genus of green algae belonging to the family Mesotaeniaceae. This genus is known to include psychrophilic species found on surfaces of glaciers and ice sheets. Recently, a mesophilic species, Ancylonema palustre, has also been discovered from the temperate moorlands of western Germany. One example of the genus is the species Ancylonema nordenkioeldii, which has been known to be an important part of the algal communities on glacial ice surfaces in Greenland and Norway. Psychrophilic members of Ancylonema have been recorded to participate in algal blooms on glacial ice surfaces,