Hydrianum

Hydrianum is a genus of green algae, in the order Chlamydomonadales. It is found in freshwater habitats such as marshes and bogs, as an epiphyte on plants or other algae.^[1] It is common, but most likely overlooked due to its similarity with similar genera such as Characium.^[3]

Hydrianum
Hydrianum ovale
Scientific classification
Kingdom:	Plantae
Division:	Chlorophyta
Class:	Chlorophyceae
Order:	Chlamydomonadales
Family:	incertae sedis
Genus:	Hydrianum Rabenhorst, 1868
Type species
Hydrianum ovale Rabenhorst[1]
Species[1]
Hydrianum coronatum Fott Hydrianum crassiapex Korshikov Hydrianum diogenes (F.W.Jane) Fott Hydrianum ellipticum Korshikov Hydrianum gracile Korshikov Hydrianum lageniforme Korshikov Hydrianum ovale Rabenhorst Hydrianum pyrenoidiferum Massjuk
Synonyms
Chlororhabdion F.W.Jane[2]

Description

Hydrianum consists of solitary or clustered cells attached to a substrate, via a mucilaginous pad or a stipe. Cells are cylindrical, oval, or spindle-shaped; in some species they are distinctly curved. Cells are uninucleate (with a single nucleus), they contain a single parietal chloroplast (or multiple when older). Pyrenoids are generally absent but may be present in a few species.^[1]

Asexual reproduction occurs via the formation of zoospores; the zoospores are released through a rupture near the apex of the cell wall, while one zoospore stays behind and develops into a new vegetative cell. Zoospores have two flagella and a single chloroplast. After swimming, the zoospores settle and develop into a new cell. Sexual reproduction has not been observed in this genus.^[1]

Members of Hydrianum with a pyrenoid can be confused with Characium, but in Hydrianum the zoospores exit subapically or apically, while in Characium the zoospores exit through a lateral opening. Additionally, in Hydrianum a zoospore may remain in the sporangium and develop into a new cell. The genus is also similar to Characiopsis, which generally lacks pyrenoids, but is unrelated.^[3]