The liverwort Plagiochila lamyana Gradst. & D.P.Costa sp. nov. is described from Mount Roraima National Park, Brazil. The new species is a member of P. sect. adianthoideae and differs from other species in this group by the narrowly elongate leaves with a bifid apex and subentire margins, large radiating trigones and opposite male bracteoles not overlapping. The new species is a further addition to the rich endemic flora of the Guayana Highland.