Dismantling the treasured flagship lichen Sticta fuliginosa (Peltigerales) into four species in Western Europe

In the framework of a worldwide project on the phylogeny of the lichen genus Sticta, dedicated sampling was performed in four regions of Western Europe, roughly along an East-West line between N 48°02’ E 07°01’ and N 52°01’ W 09°30’, ranging from France/Vosges to Ireland/Kerry. Five clearly distinct ITS haplotypes were detected for isidia-producing species where only two were expected. Subtle anatomical and morphological characters, together with a strongly supported 4-loci molecular phylogeny, permit to distinguish, besides the easily recognized S. canariensis and S. limbata:
• the two « well-known » S. fuliginosa and S. sylvatica whose type collections have been carefully reassessed; the former is widespread in both hemispheres, while the latter is correctly identified only from continental Europe and the Andes in Colombia; the barcode ITS of S. fuliginosa differs by a single substitution from S. limbata (with a single exception), and the 4-loci phylogenetic tree does not resolve them as distinct lineages, most probably highlighting a very recent divergence and incomplete lineage sorting;
• three species that were formely included in S. fuliginosa: the resurrected S. ciliata Taylor, belonging to a complex group yet to be disentangled and occurring in the Neotropics, Africa, Macaronesia and Western Europe, and two species described as new for science, S. fuliginoides, found in continental Europe, the Canary Islands, eastern North America and Colombia, and S. atlantica only known from Ireland and the Azores archipelago. Molecular inferences demonstrate active divergence and dispersion within S. ciliata that may require recognition of further species.
Fresh material can be identified with a morphological and anatomical preliminary key provided here. We propose that the taxonomy of all lichen species be urgently reviewed in the light of molecular data in an evolutionary context, particularly those used as bioindicators of environmental change and woodland management.