A new species, Lecania belgica, is described and illustrated. It is a saxicolous lichen known only from the type locality in Belgium. It is characterized by apothecia with pruinose, irregularly undulating discs, relatively short ascospores, and by having 12–16 spores in the asci. It was found on mortar together with Diplotomma alboatrum.

Two new Pertusaria species with brown ascospores are described from southern California and Baja California, Mexico. Pertusaria islandica sp. nov. is characterized by pertusariate to pseudolecanorate ascomata, ellipsoid ascospores, 8-spored asci, a strongly K+ violet reacting epithecium, and the presence of the 2′-O-methylperlatolic acid chemosyndrome, while P. occidentalis sp. nov. has pertusariate ascomata, globose to subglobose ascospores, 8-spored asci, and contains the arthothelin chemosyndrome. Pertusaria ochracea Kremp. is reduced to synonymy with P. melanospora Nyl.

Buellia nordinii, a new muscicolous or lignicolous species characterized by a blastidiate thallus containing atranorin, apothecia with a fine granular surface, markedly enlarged paraphyses tips and large triseptate ascospores is described from Venezuela. The species grows in very humid situations near the ground in open paramo vegetation at high elevations. It is compared with other known asexually reproducing and triseptate Buellia taxa.

The morphological features and chemical compounds found in the first European collection of Calicium victorianum are compared with type material from Australia of C. piperatum F. Wilson. The phylogenetic relationships of the species are discussed by comparing its nuclear rDNA ITS1-5.8S-ITS2 with that of other species of Calicium.

Two new species of Psoroma with unusual cephalodia are described: P. echinaceum with isidiate cephalodia, from southern South America and P. geminatum with fragile phyllidiate cephalodia, from New Zealand and Australia. These are additional to two previously described species producing dispersal units on their cephalodia, P. durietzii P.James & Henssen (with soredia) and P. aphthosum, Vain. (syn. nov. P. dimorphum Malme) (with isidia). This is a strategy development that ensures successful establishment of new thalli.

A key is provided to the 81 saxicolous species and infraspecific taxa of Porina Ach. (Trichotheliaceae). It includes diagnostic characters, broad distributional and some habitat information, as well as references to more complete descriptions.

The sensitivity of lichen species to air pollution was assessed by examining aspects of their rate of disappearance over a 5 year period in an area with rising SO2 concentration. These rates of disappearance were compared with the ecological index of species proposed by LeBlanc & DeSloover in 1970, i.e. the index of average number of neighbours for a given species. Linear correlation showed that this ecological index is a reasonably accurate indicator of species sensitivity. When the selection of species was performed according to criteria other than SO2 sensitivity, viz. according to the predilection of lichens for eutrophicated bark, the ecological index proved reliable only when trees whose conditions were non-optimal for this group were excluded. When applied to the group of species that avoids eutrophicated bark the ecological index proved most reliable, although the group of ‘ nitrophilous ’ species may also be used in air pollution indicator studies.