A new checklist of the lichen-forming, lichenicolous and allied fungi occuring in the British Isles (including Ireland) is presented. The total number of species accepted is 1701, distributed through 294 genera. Of these species 1471 are lichen-forming, 183 lichenicolous, and 47 allied fungi. In addition to incorporating the results of investigations published since the last checklishts, the list embodies a great deal of original work by the authors and their collaborators; as a result a considerable number of changes in nomenclature are made here for the first time, including one new genus (Herteliana) and 56 new combinations. Names utilized in previous checklists are cross-referenced and relevant papers cited under generic heads.

The macrolichen flora on trees in the Algarve is described on the basis of an examination of 105 main sites in the period 1970–76. 103 lichens are reported from the 43 phorophyte species studied, and discussions of the ecology and distributional patterns provided.

Ascus structure of eight yellow, two white and two brown Rhizocarpon species has been investigated by light microscopy. Ultrastructure and function in R. atroflavescens subsp. pulverulentum and R. montagnei were studied in TEM.

The Rhizocarpon-type ascus clearly differs from all other ascus types observed in the Lecanorales. It is bitunicate, opening with a slight ‘Jack-in-the-box’-mechanism. Its structure and function are related to patellariacean ascus types, but unlike those the ascus wall cytochemistry shows a certain similarity with Lecanora- and Peltigera-type asci. Rhizocarpon-type asci are embedded in a strongly amyloid hymenial gelatine. The nonamyloid ascus wall is surrounded by the strongly amyloid outer layer. The slightly amyloid expansible inner layer (= endoascus) is apically thickened; it shows the banded and pleated ‘accordion-structure’ characteristic of bitunicate asci. Prior to dehiscence, the ascus wall and its outer layer burst. Thereafter the pleatings of the expansible inner layer are stretched, forming the rather short beak which reaches the hymenial surface. During expansion gliding occurs between the expansible inner layer and an outer part of the endoascus, here described as the ‘inner layer’. In a few sections of aldehyde- fixed material of R. atroflavescens a small laminated plug was observed in the apex of the endoascus.

Rhizocarpon-lype asci are considered to be the most archaic in the Lecanorales. This supports a hypothesis that Rhizocarpon is a phylogenetically basal group, linking the evolved Lecanorineae, and possibly also the Peltigerineae and Teloschistineae with not yet recognized bitunicate ancestral forms similar to those occurring in the Patellariaceae.

The limestone plateau of Derbyshire is intensively farmed but supports terricolous lichens associated with unimproved grazing, derelict lead mining ground and modern fluorspar working. The assemblages identified include a number of relict species now very rare in central England. Reworking mine waste for fluorspar can result in the development of communities containing particularly interesting lichens. Land-use is now the chief determinant of terricolous lichen communities in the area studied.

Zoosporogenesis was observed in the algal symbiont (Trebouxia gelatinosa) of Parmelia caperata. This is the first detailed report of this phenomenon in a Trebouxia species and, more importantly, in lichens, where zoosporogenesis in this alga is usually suppressed and the arrested zoospores form aplanospores. Observations of zoospore formation by algal cells within the natural thallus and in thallus fragments incubated on a mineral medium suggest that zoospores are released within thalli and may escape from the thallus to form free-living microcolonies. These colonies potentially could unite with hyphae derived from spores of either the same, or genetically different mycobionts (fungal symbionts) to establish new lichen associations, as has been shown in laboratory studies. Such natural resyntheses could be one cause for the observed heterogeneity characterizing fungi in many lichen populations. Other implications of free-living Trebouxia populations are discussed.

The weathering phenomena resulting from the encrustation of basalt by Pertusaria corallina have been studied by scanning electron microscopy and a variety of other techniques. The rock consists largely of plagioclase felspar (labradorite) and ferromagnesian minerals, the latter often being replaced by hydrothermally formed ferruginous clay minerals. Lichen weathering results in the extensive etching of the primary rock-forming minerals, particularly labradorite, and in the degradation of the clay minerals to yield a thin ochreous crust of poorly-ordered ferruginous (ferrihydrite) and alumino-silicate materials. These changes are brought about principally by the oxalic acid secreted by the mycobiont, a conclusion supported by observations following experimental mineral alteration.

The nomenclature and in part also the taxonomy of the following European lichens is discussed: Cladonia cervicornis (Ach.) Flotow subsp. cervicornis and subsp. verticillata (Hoffm.) Ahti comb. nov., C. bacilliformis (Nyl.) Glück, C. portentosa (Dufour) Coem., C. anomaea (Ach.) Ahti & P. James comb. nov. (syn. C. pityrea (Flörke) Fr.), C. conista Robbins ex Allen, C. conoidea Ahti sp. nov. (syn. C. conistea sensu Asah.: contains atranorin and fumarprotocetraric acid, type from England), C. bacillaris Nyl., C. coniocraea auct., and C. ochrochlora Flörke.

The African lichen ‘Cladonia gorgonina (Bory) Eschw.’ is typified and its nomenclatural status reconsidered. Under the valid name Cladonia gorgonea Eschw. it is reduced to the synonymy of Cladia aggregata (Swartz) Nyl. The correct name for Cladonia gorgonina auct. is C. glaucopallida Vainio. A list of the new lichen taxa proposed by J. B. Bory, which were invalidly published by Flörke in 1809, is also presented.

Sociological tables are given for five communities found on Alnus incana in Troms, North Norway: Arthopyrenietum punctiformis P. James et al., Lecanoretum chloropoliae ass. nov., Lecanoretum subfuscae Hil., Lobarion pulmonariae Ochsn. and Parmelietum olivaceae Barkm. Snow cover and shading from large ferns are important factors governing the distribution of the communities on the tree trunks.

At present 40 species of Pseudocyphellaria are recognised in the New Zealand flora, ten of which appear to be new and will be described elsewhere. In the present account, the 30 published taxa are listed alphabetically and, where applicable, the synonymy of confused species is discussed. The following 13 new combinations are made: P. coerulescens (Mont.), P. condensata (Zahlbr.), P. coriacea (Hook.f. & Taylor), P. delisea (Fee), P. dissimilis (Nyl.), P. hookeri (Church.Bab.), P. lividofusca (Krempelh.), P. moruagnei (Church. Bab.), P. multifida (Laurer), P. poculifera (Miill.Arg.), P. psilophylla (Miill.Arg.), P. pubescent (Miill.Arg.), and P. rubella (Hook.f. & Taylor). 85 taxa are reduced to synonymy with known species.

A simple scale using tropical lichen species has been used by secondary school students to assess air pollution zones in Hong Kong. The distribution of lichens was found to be related to the sites of power stations, a desalting plant, and heavily industrialised areas. As in temperate climates, both complexity of growth form and numbers of species increase with distance from the sources of air pollution.

Lobes of Xanthoria elegans are shown to be engulfed by more rapidly growing neighbouring lobes, thereafter ceasing to grow, and the rate of lobe engulfment increases with thallus age. Similarly, growth can cease when lobes of adjacent thalli meet. Mature central areas of eroded thalli may regenerate lobes and resume growth. In Buellia coniops, B. russa and Caloplaca cirrochrooides, peripheral concentric zonation does not always correspond to a single year's growth, and one zonation effect is correlated with an unusually severe winter.

Fifteen specimens of four Acarospora species of subgenus Xanthothallia were analysed. All species contained (+)-rhizocarpic acid. A. gobiensis and A. schleicheri had only this compound and A. oxytona this and (+)-lichesterinic acid. A. chlorophana seems to exist in two chemical races, one with a mixture of (-)-acaranoic and (-)-acarenoic acids and the other with (+)-roccellic acid. The stereochemistry and biogenesis of these compounds is briefly discussed.

Bryoria chalybeiformis, as commonly interpreted, is an almost exclusively saxicolous or terricolous species with a largely arctic-alpine distribution; it produces small amounts of fumarprotocetraric acid in the soralia. The terricolous form of B. fuscescens var. positiva, distributed from sea level to the high mountains, is distinguished by the production of abundant fumarprotocetraric acid accompanied by protocetraric acid. B. intricans appears to be closely related to B. chalybeiformis and may possibly represent an environmentally induced morphotype of it. Attention is drawn to nomenclatural problems connected with B. chalybeiformis.

A lichen flora of Northumberland is presented; it accepts 589 species. During the preparation of this work 7 lichens new to Britain and 271 new to the county were discovered. Complementing the species inventory is an analysis of factors affecting lichen distribution, a description of the major lichen habitats and a section on the history of lichen recording. Extensive tracts of semi-natural vegetation, steep climatic gradients and some of the least polluted air in England provide conditions suitable for a rich lichen flora; 40% of the British species have been recorded. Particularly notable habitats are sandstone crags in the uplands, Whin Sill (basalt) outcrops and sites contaminated with heavy metals. The County contains a major parkland, and several sites with a lichen flora characteristic of ancient woodland. A short list of lichenicolous fungi is included.