Usnea is a cosmopolitan genus of lichen-forming Ascomycota (Parmeliaceae, Lecanorales). This hyperdiverse genus remains poorly known, especially in tropical regions, and recent efforts have been made to clarify the species concepts and describe the diversity of species. We describe five new species from tropical South America based on morphological and chemical features supported by molecular data from the ITS rDNA, nuLSU, RPB1 and Mcm7 markers. Usnea clerciana is a Galapagos endemic characterized by inflated branches holding elongated tubercles, excavate soralia and/or apothecia. Usnea aranea and U. subaranea share inflated branches with numerous papillae and a loose arachnoid medulla, but differ in the minute and irregular soralia in U. aranea, that are circular and excavate in U. subaranea. Usnea rubriglabrata and U. subglabrata are characterized by inflated branches with excavate soralia, with a reddish cortex pigmentation in U. rubriglabrata that is lacking in U. subglabrata. Usnea aranea, U. rubriglabrata, U. subaranea and U. subglabrata are so far endemic to continental South America; the three former species are closely related and cluster in a highly supported clade, characterized by species distributed in the tropical Andes. New records for the region are provided and U. moreliana is resurrected, corresponding to the valid name for U. rubricornuta.

The diversity of pendulous Usnea species in tropical South America (Bolivia, Brazil, Colombia, Ecuador, Paraguay, Peru and Venezuela) and the Galapagos Islands is discussed with reference to 23 species. Usnea crenulata Truong & Clerc is newly described. Usnea articulata, U. deformis, U. dimorpha, U. geissleriana, U. merrillii, U. perhispidella, U. sanctaeritae, U. subflammea and U. transitoria are newly reported for South America. Modern descriptions are provided for Usnea amabilis, U. arthroclada, U. dodgei, U. humboldtii and U. regia. We propose to reject the synonymy of U. hesperina with U. schadenbergiana, and the valid name for U. hesperina is therefore U. subgracilis. Distinct patterns of unidentified triterpenoids have been detected by thin-layer chromatography and are used to characterize several species within this group. The morphology, branch anatomy, chemistry, ecology and distribution of each species are given, together with an identification key.

In North America the names Punctelia subrudecta and P. perreticulata have variously been applied to corticolous sorediate Punctelia specimens with lecanoric acid and a pale lower surface. ITS1, 5.8S, and ITS2 sequence data were generated from a geographically and morphologically broad sampling from within these specimens, and a molecular phylogeny was inferred. A combined approach using morphology, geography, and phylogeny was used to circumscribe three distinct species in North America, one of which is described as new to science (P. caseana), one of which is finally confirmed for the continent (P. jeckeri), and one whose original circumscription is validated (P. perreticulata). The phylogeny inferred from ITS sequence data supports the taxonomic value of the following morphological characters for distinguishing species in this group: presence/absence of pruina; conidium type and length (although see discussion of P. jeckeri), and presence/absence of scrobiculae on the upper surface. A key to the North American species of Punctelia is provided.

135 infrageneric taxa of epiphytic lichen were found in 20 stands of tree-line forests of the Central-Eastern Italian Alps. Three forest types were considered: (1) late successional stands with several large trees, (2) pioneer stands on abandoned pastures without large trees, and (3) open and grazed stands. They were compared on the basis of four main criteria: (1) species richness, (2) number of rare species, (3) number of species that are exclusive to the subalpine belt in Italy, and (4) number of species that are exclusive to the Alps in Italy. Species richness is higher in the late successional stands, which also host a higher share of rare and exclusive species. The total number of rare species per site is correlated with the total number of species, as well as with the number of common species, and with the total number of macrolichens. Rare macrolichens are correlated with common macrolichens. Two main groups of target species with decreasing conservation priority are identified. Letharia vulpina is suggested as signal species for sites worthy of conservation. The guild of macrolichens may be used as an indicator of both species richness and of the occurrence of rare species.

Concentrations of mercury were measured in soil and two species of epilithic macrolichens (Umbilicaria decussata and Usnea antarctica) collected along of the coast of northern Victoria Land coast. Most of the soil samples had a very low mercury content, whereas lichens had levels higher than in other remote areas. Although a possible contamination of samples cannot be completely excluded, the relevance to bioaccumulation of the very slow growth rate of lichens and of volcanic activity are discussed.