Since the last compilation in 1983, the number of lichenicolous fungi (and lichenicolous lichens) recorded in Great Britain and Ireland has increased from 218 to 403 species (a rise of 85%). The introduction includes accounts of: the history of investigation, circumscription, phylogenetic relationships, symbiotic interactions, dispersal and establishment, distribution, culture, host restriction, and identification. The checklist enumerates the recorded species. Information is provided on the systematic position of each genus, together with the authors and dates of publication of all accepted names; synonyms used in the literature of the two countries since 1910 are cross-indexed. References to pertinent literature with descriptions and discussions are included, together with notes on particular species. The list of references cited includes 298 publications. The following new scientific names are introduced: Diederichia gen. nov., and Dactylospora scapanaria (syn. Lecidea scapanaria), Diederichia pseudevemiae (syn. Macrophomina pseudeverniae), Muellerella ventosicola (syn. Microthelia ventosicola) and Nigromacula uniseptata (syn. Vouauxiella uniseptata) combs, nov.

Pyrenula luteopruinosa Etayo & Aptroot is described as new from lowland rainforest on the Pacific coast of Panama. The new name Pyrenula caraibica Aptroot & Etayo and the new combinations Pyrenula chilensis (Fée) Aptroot & F. Berger, Pyrenula cryptothelia (Müll. Arg.) Aptroot & Etayo and Pyrenula hibernica (Nyl.) Aptroot are proposed.

Trichothelium longisetum sp. nov. (Porinaceae) is described from a rainforest in northeastern Ecuador. It has a non-radiating photobiont, prominent, black perithecia, each with numerous, long-acute to acicular, black setae, and elongate-bacilliform, 9–15-septate ascospores. Remarkably, this lichen grows on wood rather than on the living leaves or bark of trees or shrubs. Four species of Porina are also reported for the first time from Ecuador.

Chroodiscus lomatiae Messuti, Lumbsch & Vezda is described as new to science. This southern South American species belongs to the family Thelotremataceae. It is characterized by fusiform, hyaline, small, thin-walled ascospores, exfoliating, chroodiscoid apothecia, and the presence of lecanoric acid.

Soft unprotected sea cliffs and slopes were surveyed at forty localities around the English coast and found to support a restricted lichen flora that was zoned in relation to sea-level. Bed rock composition, structural heterogeneity and high levels of instability largely control the terricolous lichen vegetation, which is predominantly composed of calcicoles typical of early successional stages. Cyanobacterial lichens are well represented. The species encountered can be arranged into three provisional assemblages characteristic of alkaline bed rock, acidic bed rock, and turf edges. Few species with maritime affinities were present but this group included rarely recorded species of Pyrenocollema and abundant Lecanora zosterae. Other rare and unusual lichens were present, often at a low density and in only a few localities. The lichen flora of soft cliffs has links with that found on urban wasteland and, remotely, with that of sand dunes.

The factors influencing the predominance of one of the two mineral forms of calcium oxalate (CO), the monohydrated whewellite (COM) and the di-hydrated weddellite (COD), forming the pruina of the upper cortex of lichens, have been investigated through a simple, sensitive histochemical assay: toluidine blue O (TBO), a metachromatic staining test. The differential reactivity of 43 thalli of 17 pruinose foliose species, supplemented by X-ray diffraction analysis and observations with polarizing and scanning electron microscopy, suggests that the histochemical reactivity of hyphal walls and cementing substances of the upper cortex are related to the density of anionic charges. These factors are probably due to the occurrence of polyuronic acid substances that strongly affects the mineralization of CO. Di-hydrated wedellite is always associated with TBO metachromatic reactivity, and COM with orthochromatic reactivity. When the material has an ambiguous ortho/metachromatic reactivity, COD and COM may occur together. This study presents the first experimental evidence that in lichens CO biomineralization is at least partially biologically controlled.