A new lichen genus, Rolfidium, in the family Bacidiaceae is described, with R. peltatum as type species. It is known only from one locality in Sri Lanka.

Pannaria is shown to include species whose thallus ranges from the almost homoiomerous to the fully differentiated heteromerous state. A new species of Pannaria is described, P. santessonii, with a thallus closely resembling that characteristic of the Collemataceae. Lepidocollema carassense Vainio and Lepidoleptogium montaguei A. L. Sm., the type species of these respective genera, have beenfound to have a similar type of thallus. Further study of the relationship between thesegenera is needed.

Rhizocarpon (subgenus Phaeothallus) santessonii sp. nov. is described from Norway. The species grows immersed in the areolae of Tremolecia atrata when young and later develops autonomous areolae. The species is further characterized by a yellowish grey thallus containing an unidentified pigment, a non-amyloidmedulla, and 1-septate spores which are persistently colourless or become unevenly brownwith age.

Nectriella santessonii sp. nov. (Hypocreales) on Anaptychia runcinata (With.) Laundon, is introduced for a species that previously has been confused with N. tincta (Fuckel) R. Sant. The two species are distinguished by several fundamental characters. The growth of single ascospores in pure culture has proved the connection between the new species and an Acremonium anamorph.

Histochemical aspects of the amorphous layers in two species of Parmelia apseudocyphellate and a pored epicorticate, were compared. In P. saxatilis this layer, called the ‘ syncortex ’ (a new term), is composed of strongly acidic (sulphated) polysaccharides containing hyaluronic acid. It is easily distinguishable histochemically from the cortical interhyphal matrix. In P. caperata the mild acidic polysaccharidic composition of the epicortex and the interhyphal matrix is shown. The function of these amorphous layers is discussed on the basis of these results.

The spatial distribution of corticolous lichens was studied along Big Seven Mile Creek (Cabell County, West Virginia, U.S.A.), a small stream that was periodically inundated by floodwaters carrying heavy loads of sediment. Lichen communities located at 0, 1.0 and 1.5 km from the confluence with the Ohio River were compared using step-wise discriminant analysis, a multivariate technique. Of the physical factors tested, the results indicated that the sediment on the tree boles was the most important factor separating the three stations and bole heights. Species richness was established to be an important mensurational variable separating stations, bole heights, and parallel and perpendicular transects. Changes observed in lichen community structure are assumed to have resulted from microclimatic variation brought about primarily by sedimentation associated with flooding. Failure of the physical factors and biotic variables to separate tree bole aspects (faces of boles in respect to the stream) indicate that abrasion and current-induced exfoliation are not important factors affecting lichen communities in the study area. Corticolous lichens occurring along streams subject to periodic inundation may represent a useful indicator in studies of flooding, water quality, and/or sedimentation in watersheds.

The effects of several elements of floristic structure and bioindication study design on the predictive power of the Index of Atmospheric Purity (IAP) proposed by LeBlanc & De Sloover were studied using Monte Carlo simulation. The predictive power was assessed by the correlation coefficient of the IAP value, computed under specified assumptions, and the stand position along a simulated pollution gradient. The effects of seven parameters were studied: proportion of sensitive and poleophilous species, species frequency distribution, size of total species pool, number of stands, distribution of stands along the air pollution gradient and index choice. The simulations showed that the median predictive power of such studies is affected mainly by the proportion of sensitive and poleophilous species, the number of species, and distribution of trees along the pollution gradient. The variance of the predictive power is influenced mainly by the proportion of sensitive species, frequency distribution, number of stands and distribution of stands along the pollution gradient. Recommendations for further bioindication studiesare given.