A molecular phylogenetic evaluation of the Ramalina siliquosa complex, with notes on species circumscription and relationships within Ramalina

Lichens of the Ramalina siliquosa complex dominate seashore cliffs in Europe and Southeast Asia, but their taxonomy has been vigorously debated for over a century. On many cliffs, they exhibit a bewildering zonation of chemotypes that resembles the classic zonation of organisms that occupy the littoral zone below. Do the chemotypes represent separate species, or infraspecific variation? To better understand the systematics of this group, sequences from four genetic loci (ITS, IGS RPB1 and RPB2) were obtained for 59 samples from Denmark, France, Iceland, Norway, the UK, Japan and Korea, including all major chemotypes. Maximum likelihood analysis of these sequences, together with sequences from 36 other Ramalina species, reveals that the complex comprises two distinct phylogenetic lineages, each including multiple chemotypes. These two putative species-level lineages correspond to the currently accepted taxa R. cuspidata and R. siliquosa. There is no evidence that these two species are ph...