Kalmar "iri fern" tana nufin rukunin tsire-tsire masu kama da fern waɗanda suke da yawa a zamanin Paleozoic (kimanin shekaru 360-250 da suka wuce). Wadannan tsire-tsire suna da sifofi irin na iri, wanda yayi kama da na zamani gymnosperms (tsiran da ke samar da iri amma ba furanni ba). Furen iri suna da manyan kusoshi kuma ana haifuwa ta hanyar iri maimakon spores, wanda ke bambanta su da ferns na gaske. Suna da sha'awar masana burbushin halittu domin suna wakiltar muhimmiyar hanyar haɗin kai a cikin juyin halittar iri na zamani.