An artificial key for the identification of 218 lichen-forming, parasitic, parasymbiotic and saprophytic fungi reported as occurring on lichens in the British Isles is provided. Agyrium flavescens Rehm, Cyphelium marcianum B. de Lesd., Scutula krempelhuberi Körber and Stigmidium solorinaria (Vainio) comb. nov. are reported from the British Isles for the first time, and three further new combinations are made: Bacidia killiasii (Hepp) comb, nov., Pleospilis ascaridiella (Nyl.) comb. nov. and Polycoccum gelidaria (Mudd) comb. nov. References to publications in which further information on the species can be found are included. Illustrations of the spores of 141 species and an index to the names of fungi and hosts are also presented.

Microglaena nidarosiensis Kindt has been rediscovered after 100 years on the west-coast of Norway. It is shown to be identical with Clathroporina calcarea W. Watson, and to belong in the genus Belonia which is placed in the Gyalectales as B. nidarosiensis (Kindt) comb. nov.

The genus Clathroporina is typified on C. olivacea Müll. Arg., and is shown not to be present in Europe. C. caudata Vězda & Vivant is transferred to Belonia as B. caudata (Vězda & Vivant) comb. nov.

This comparative investigation on ascus fine structure and function substantiates the findings of Chadefaud (1960) and his coworkers indicating a close taxonomic relationship between the Baeomycetaceae and Leotia, a non-lichenized member of the Helotiales, rather than between the Baeomycetaceae and the Cladoniaceae and other members of the Lecanorales. Besides the distinct differences in ascus structure and function, cytological divergences were noted between the Baeomycetaceae and Leotia on one hand, and Cladoniaceae on the other. The occurrence of glycogen in the Baeomycetaceae and Leotia, but not in the Cladoniaceae and other members of the Lecanorineae, and the differences in phycobiont preference and thus in the mycobiont–phycobiont contact in the Baeomycetaceae and Cladoniaceae were discussed.

The cortical structure of Usnea subfloridana and algal cell division within the thallus, is illustrated and described.

By using a dissection technique it was demonstrated that binding of Ni2+ ions occurred to both the algal zone and fungal medulla in various species of the lichen genus Umbilicaria. The algal zone, fungal medulla and lower surface plates in Umbilicaria muhlenbergii accumulated 21, 52 and 27% respectively of the total Ni2+ ions taken up. The amount of Ni taken up varied in different species of the same genus but in general the uptake by Peltigera (over 70 μmol g−1 dry weight) was some three times that by Umbilicaria under the same conditions.

The vanadium content of the lichen Hypogymnia physodes was determined in the vicinity of a power plant using heavy oil as fuel. For the chemical analysis a DC plasma emission spectrometer was used. Air dried samplesof the lichen contained between 1–4 and 57 parts per million (ppm) of vanadium. The highest concentrations were found in specimens collected less than 1 km from the power plant. Lichens collected 50 km from the plant contained less than 2 ppm of vanadium.