A molecular phylogenetic evaluation of theRamalina siliquosacomplex, with notes on species circumscription and relationships withinRamalina

摘要

Lichens of theRamalina siliquosacomplex dominate seashore cliffs in Europe and South-East 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,RPB1andRPB2) were obtained for 59 samples from Denmark, France, Iceland, Norway, UK, Japan and Korea, including all major chemotypes. Maximum likelihood analysis of these sequences, together with sequences from 36 otherRamalinaspecies, reveals that the complex comprises two distinct phylogenetic lineages, each including multiple chemotypes. These two putative species-level lineages correspond to the currently accepted taxaR. cuspidataandR. siliquosa. There is no evidence that these two taxa are phylogenetic sister species. Consequently, the explanation of this chemotype complex as an example of 'sibling speciation' is rejected. Specimens traditionally called 'R.siliquosa' from South-East Asia form a third clade, identified here asR.semicuspidata, with an additional, divaricatic acid chemotype. Other results include a robustly supported clade ofRamalinaspecies that produce medullary depsides and depsidones; this clade includes another well-supported clade of south-eastern United States coastal plain and tropicalRamalinaspecies. By contrast, large, strap-shapedRamalinaspecies that lack medullary depsides and depsidones occur in separate lineages. In addition, close relationships between the following groups of species are indicated:R. farinaceawithR. subfarinacea;R.fraxineawithR. leptocarpha,R. menziesiiandR. subleptocarpha;R. sinensiswithR. unifolia. Furthermore, a new, variolaric acid-only chemotype is reported forR.farinacea, and a new, acid-deficient chemotype is reported for a more broadly circumscribedR. culbersoniorum.