laiken wani hadadden kwayoyin halitta ne wanda ke tasowa daga algae ko cyanobacteria wanda ke zaune a tsakanin filaments na fungi nau'in Laikens sune muhimman ƴan wasan motsa jiki a hawan keke na gina jiki kuma suna aiki a matsayin masu samarwa waɗanda yawancin masu ciyar da abinci na trophic suna ciyarwa, irin su reindeer, gastropods, nematodes, mites, da springtails. Laikens suna da kadarori daban-daban da na kwayoyin halittarsu. Suna zuwa cikin launuka da yawa, girma da siffofi kuma wasu lokuta suna kama da tsire-tsire, amma ba shuka ba ne. Suna iya samun ƙananan rassan rassa marasa ganye ([frutikos]); Tsarin lebur-kamar ganye (folios); suna girma kamar ɓawon burodi, suna manne da ƙasa (substrate) kamar kauri mai kauri ([crustose]]).

Laiken-su suna fitowa daga tsayin teku zuwa tsayin [[[yanayin tudu | tsayi], a yawancin yanayin muhalli, kuma suna iya girma a kusan kowane saman. Suna da girma akan haushi, ganye, ganyaye, ko wasu laikens da kuma rataye daga rassan "rayyukan iska" ([epiphyte]] s) a cikin dajin mai zafin jiki. Suna girma a kan dutse, bango, kabari, [rufin]] s, saman ƙasa da ba a iya gani ba, roba, ƙasusuwa, da cikin ƙasa a matsayin wani ɓangare na kwayoyin ƙasa na halitta. Laikens iri-iri sun dace da rayuwa a wasu wurare masu tsananin muni a Duniya: Arktik tundra, bushe bushe desert s, rocky Coast s, da tsibi mai guba slag. Suna iya zama har ma a cikin dutse mai ƙarfi, suna girma tsakanin hatsi ([Endolitik laiken | endolitik]]).