Bryona tortuosa is reported as new to northern Europe. Notes on its morphology, chemistry, ecology and distribution are given and the distinction from its closest ally, B. fremontii, is discussed.

A new species of Collema is described which, like C. callibotrys, has numerous minute globose apothecia in clusters but, unlike that species, has unornamented spores. It is recorded from Tanzania and Uganda.

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.

Mature as well as juvenile stages of thalli and apothecia occurring on numerous meteorite fragments found on Ella Island can be referred to 10 genera of lichens: Acarospora, Candelariella, Gyalidea, Lecanora, Lecidea, Physcia, Pseudephebe, Polysporina, Rinodina and Xanlhoria. In their colonization phase these lichens are influenced by the mineralogy and chemistry of the meteorite fragments. Thus Xanlhoria shows a distinct preference for the meteorite minerals rich in iron, whereas Candelariella appears to avoid these minerals.

The lichen floras occurring on high-level quartzite, Moine granulite, syenite and calcareous schist in the northern Highlands of Scotland are compared. Rock mineralogy is of overriding importance in determining the assemblages present, though this factor can be modified by extraneous nutrients. Local climatic conditions favour a cloud zone community dominated by ‘alectorioid’ species, produce stony ablation surfaces at a low level and allow maritime species to grow far inland. Ben Hope, with 34 ‘ rare ’ species recorded, is confirmed as a major site for alpine calcicolous lichens. Lecanora chlorophaeodes Nyl., a species new to Britain, is reported from the summit of Ben Loyal. In contrast, the extremely hard, acid, nutrient-deficient quartzite of Foinaven displayed a flora characterized by a very low species diversity.

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.