Oceanic islands are important sources of biodiversity. Island radiations have largely contributed to the diversity of many groups of extant organisms such as the Anolis lizards of the Caribbean and the silversword alliance in Hawaii. However, rapid speciation in island radiations can lead to vague species boundaries, due to morphological stasis coupled with allopatric speciation or because morphological diversification has not had time to happen. Scarce examples of island radiations are known for lichen-forming fungi. Ramalina is a genus of lichen-forming fungi with c. 200 species known worldwide. In Macaronesia it shows high diversity (c. 40 species), coupled with high levels of endemicity (c. 50%). These figures are remarkable considering most lichen-forming fungi show very wide distribution ranges. According to recent results, most of the endemic diversity is the result of a single Macaronesian radiation, which might have an adaptive basis. In this study, we focus on the Ramalina decipiens group, which shows its highest diversity in the Canarian archipelago and has several single-island endemisms. The R. decipiens group is defined by its saxicolous habit, fruticose thalli and the presence of chondroid strands adjoining the cortex. The last taxonomic review of the group dates back from 1980 and included four species. Subsequent studies on the Madeira archipelago found two species endemic from Porto Santo. Based on a broad sampling in the Canary Islands, Madeira and Cape Verde (>300 individuals), we revisited the group’s taxonomy following an integrative approach. We studied species boundaries using morphological, chemical and molecular (6 markers) datasets. Our results highlight that the diversity of the group has been clearly underestimated in previous works, and that the assumed morphological and chemical plasticity of some species actually corresponds to independent and well-delimited lineages. This work was supported by the grant CGL2016-81136-P from the Spanish Ministry of Science and Innovation.
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