The inhibitory action of aqueous extracts from detached podetia of heathland Cladonia spp. and leachates from transplanted Cladonia turfs was tested using seeds of Avena fatua, Calluna vulgaris and Deschampsia flexuosa. Significant inhibitory effects were found for each species. Further evidence from a field experiment suggests that patches containing a mixture of Cladonia spp. can inhibit germination or establishment of vascular species, probably through both chemical and physical processes, and thus maintain intact lichen patches in otherwise closed heathland stands.