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 characteristic of the genus. Spirogyra species, of which there are more than 400, are commonly found in freshwater habitats. Spirogyra measures approximately 10 to 100 μm in width and may grow to several centimetres in length. It is often observed as green slimy patches on the ground near ponds and other water bodies having stagnant water. General characteristics Spirogyra is very common in relatively clear eutrophic water, developing slimy filamentous green masses. In spring Spirogyra grows under water, but when there is enough sunlight and warmth they produce large amounts of oxygen, adhering as bubbles between the tangled filaments. The filamentous masses come to the surface and become visible as slimy green mats. Spirogyra has a cell wall, nucleus, pyrenoid, and spiral chloroplasts. Reproduction Spirogyra can reproduce both sexually and asexually. In vegetative reproduction, fragmentation takes place, and Spirogyra simply undergoes intercalary cell division to extend the length of the new filaments. Sexual reproduction is of two types: Scalariform conjugation requires association of two or more different filaments lined side by side, either partially or throughout their length. One cell each from opposite lined filaments emits tubular protuberances known as conjugation tubes, which elongate and fuse to make a passage called the conjugation canal. The cytoplasm of the cell acting as the male travels through this tube and fuses with the female cytoplasm, and the gametes fuse to form a zygospore. In lateral conjugation, gametes are formed in a single filament. Two adjoining cells near the common transverse wall give out protuberances known as conjugation tubes, which further form the conjugation canal upon contact. The male cytoplasm migrates through the conjugation canal, fusing with the female. The rest of the process proceeds as in scalariform conjugation. The essential difference is that scalariform conjugation occurs between two filaments and lateral conjugation occurs between two adjacent cells on the same filament. Species The following species are currently accepted: Spirogyra abbreviata Zheng Spirogyra acanthophora (Skuja) Czurda Spirogyra acumbentis Vodenicarov Spirogyra adjerensis Gauthier-Lièvre Spirogyra adnata (Vaucher) Kützing Spirogyra adornata Ling Spirogyra aequinoctialis G.S.West Spirogyra affinis (Hassall) Petit Spirogyra africana (F.E.Fritsch) Czurda Spirogyra ahmedabadensis Kamat Spirogyra alpina Kützing Spirogyra alternata Kützing Spirogyra amplectens Skuja Spirogyra ampliata L.Liu Spirogyra anchora Skuja