We used δ13C values to identify lichen metabolism in the globally distributed Early Devonian (409 386 Ma) macrofossil Spongiophyton minutissimum</em>, which had been alternatively interpreted as a green plant of bryophyte grade or as a lichen, based on its morphology. Extant mosses and hornworts exhibited a range of δ13Ctissue values that was discrete from that of extant lichens. The δ13Ctissue values of 96 S. minutissimum</em> specimens coincided with δ13Ctissue values of extant lichens. In contrast, S. minutissimum</em> δ13Ctissue values showed no similarity to bryophyte carbon isotope values. The identification of large global populations of lichens during the Early Devonian may indicate that lichen-accelerated soil formation fostered the development of Paleozoic terrestrial ecosystems.