More than 400 species of Spirogyra have currently been catalogued, all of which can be differentiated by the spores they produce during sexual reproduction. Spirogyra usually reproduce via vegetative means, individual filaments fragmenting to form new algal strands. However, during periods of poor environmental conditions, Spirogyra may switch to a sexual means of proliferation. Adjacent filaments are capable of extending conjugation tubes toward each other in order to exchange genetic material and produce a zygospore, which is protected by a thick cellular wall that enables it to survive in sediment until more favorable conditions emerge.