Spirogyra is free-floating green algae present in freshwater habitats such as ponds, lakes, etc. Spirogyra is commonly known as water silk or pond silk. They have a filamentous and unbranched vegetative structure. There are around 400 species of Spirogyra found.
Cells are joined end-to-end in an unbranched, largely unspecialized, stiff filament and are cylindrical with one or two spiral-wound chloroplasts, many of which are pyrenoids are borne. The cell wall consists of two layers, the cellulose outer and the pectin inner. Filaments can be in the length of several centimetres. It has a very silky feel and a bright green colour.