Spirogyraceae

Spirogyra (common names include water silk, '''mermaid's tresses, and blanket weed') is a genus of filamentous charophyte green algae of the family Spirogyraceae, named for the helical or spiral arrangement of the chloroplasts that is characteristic of the genus. Spirogyra species, of which there are more than 500, are commonly found in freshwater habitats. Spirogyra'' measures approximately 10 to 150 micrometres in width (though not usually more than 60) and may grow to several centimetres in length.

Sirogonium is a genus of filamentous charophyte green algae of the order Spirogyrales. It is found in freshwater areas on all continents but Antarctica. Spirogyra measures approximately 32–115 μm in width. Each cell contains 2–10 chloroplasts in a ribbon, in contrast to the closely related genus Spirogyra, which has chloroplasts in a coil. Molecular phylogenetic studies have placed Sirogonium inside a clade consisting of Spirogyra species; in other words, Spirogyra is paraphyletic with respect to Sirogonium.