The green alga Printzina (Trentepohlia) lagenifera was found in southern Finland in the sori of the leaves of the indigenous fern Polypodium vulgare. The find is noteworthy because P. lagenifera occurred epiphyllous in a boreal, natural habitat. The subcosmopolitan P. lagenifera is a collective species; it was described from a hothouse in Germany. Two earlier finds from Finland are likewise from hothouses. The present alga is hardly conspecific with these lignicolous hothouse algae that most probably are introductions from the tropics. Another green alga, the common Desmococcus olivaceus (Chaetophorales) is reported to occur in Finland on the upper surfaces of the leaves of Polypodium vulgare.