Most lichenized fungi produce abundant sexual structures, and in many species sexual spores seem to provide the only means of dispersal. For example, 90% of lichens found in Great Britain and Ireland produce ascomata (fruit bodies) containing sexually derived ascospores, whereas only 29% form symbiotic vegetative propagules. Sex in lichenized fungi has been assumed to equate with outcrossing3, but failure to induce sexuality in vitro has prevented experimental investigation of their breeding systems.