Psorophorus and Xanthopsoroma, two new genera for yellow-green, corticolous and squamulose lichen species, previously in Psoroma

Abstract

Psoroma microlepideum is reduced to a synonym of P. fuegiense. The species differs in several characters from P. pholidotum, and it overlaps geographically with the latter, which is neotypified here. These two species are now placed in the new southern South American genus Psorophorus, differing from Psoroma s. str. in being corticolous, having adpressed squamules on a distinct, dark prothallus, lacking melanins, having a thin cortical layer and a simpler IKI+ apical ascus structure. Two other widespread, panaustral species are the only ones in Pannariacae containing usnic acid. The primarily fertile species has been known as Psoroma pholidotoides, but the type contains pannarin rather than usnic acid, and the correct name for the primarily fertile taxon with usnic acid is Psoroma contextum Stirt. This is together with P. soccatum R. Br. ex Crombie is now placed in the new genus Xanthopsoroma. In addition to usnic acid, both species have a series of distinct terpenoids, some in major quantities. Like Psorophorus, they are corticolous, but have long, more or less nodulose, apical perispore extensions, and an IKI+ apical ascus tube structure which is longer and thinner, including a diffuse tholus reaction, and often an external apical sheet. Phylogenetically, these two genera are shown to be monophyletic and different from Psoroma s. str. based on an analysis of ITS and nrLSU rDNA. This analysis also shows that among the ten species focused on in this study, nine species (two in Xanthopsoroma, two in Psorophorus and five in Psoroma s. str.) are monophyletic, based on two to six sequences of each species. Psoroma hypnorum remains polyphyletic. All names now belonging in Psorophorus and Xanthopsoroma are typified.