The term ‘cladoniiform lichens’ is applied to a group of lichen-forming discomycetes which either produce a ‘dimorphous’ thallus (differentiated into vertical and horizontal structures) or which resemble such lichens in having somewhat similar fruticose thalli and related phenolic chemistry. Seventeen genera comprising the families Cladoniaceae, Heterodeaceae, Cladiaceae, Baeomycetaceae and Siphulaceae are included in the group. A podetium is defined as a lichenized, stem-like portion (stipe) bearing the hymenial discs, and sometimes conidiomata, in a fruticose, simple or compound apothecium. The terminal structures commonly called apothecia on podetia or other ascomatal stipes in lichens are not whole apothecia but separate hymenial discs of a polydiscoid ascoma. In spite of superficial similarity in gross morphology and phenolic composition, the cladoniiform lichens are a life-form group rather than a taxonomic entity.

On the basis of light microscopic (LM), scanning electron microscopic (SEM) and transmission electron microscopic (TEM) investigations the Pertusaria-type of ascus is described as a particular functional type. The functionally unitunicate Pertusaria-type is characterized by its structure, staining properties, and by its particular mode of dehiscence. Tripartite ascus walls were observed in LM and TEM. The non-amyloid ascus wall is surrounded by a thin, amyloid outer layer. Both become amorphous at maturity and partly disintegrate. An apically thickened, amyloid inner layer reaches the base of the ascus. In its fine structure this amyloid inner layer resembles the material of the amyloid dome of Lecanora-type asci. It plays an important role during dehiscence and spore discharge. An elongation process was observed prior to dehiscence, at the end of which the ascus tip is situated above the hymenial surface. Dehiscence occurs by bursting or splitting of the whole ascus tip. The Pertusaria-type might represent a side-branch of evolution from bitunicate to unitunicate forms within the Lecanorales.

Pertusaria-type asci are restricted to a small number of genera within the Pertusariaceae. A considerable heterogeneity in ascus structure and staining properties was observed within the Pertusariineae sensu Henssen & Jahns (1973) and Henssen (1976).

A synopsis of 26 species belonging to 10 genera of Caliciales (s.lat.) occurring in Costa Rica is given. Short comments on the ecology and distribution of the species, indications of occurrence of secondary substances, and observations on the ultrastructure of the spores in some species are included. The mainly tropical genera Pyrgidium, Schistophoron and Tylophoron are given particular attention. Seventeen species are new to Central America and the following five new to science: Caliciurn constrictum sp. nov., Chaenothecopsis rubina sp. nov., Coniocybe sanguinea sp. nov., Schistophoron variabile sp. nov., and Tylophoron crassiusculum sp. nov. Two new combinations, Mycocalicium albonigrum (Nyl.) comb. nov. and Pyrgidium montellicum (Beltr.) comb, nov., are made. Lectotypes have been designated for Tylophoron annulatum Krempelh., T. cupulare Vainio, T. moderatum var. consociata Vainio and T. rufocapillatum Nádv. Names of several taxa in Pyrgidium and Tylophoron have been put into synonomy. Arthothelin, thuringione and thiophanic acid (in Calicium hyperelloides Nyl.) and lecanoric acid, 2'-O-methylperlatoic acid and lichexanthone (in Tylophoron) are reported for the first time in the Caliciales.

Eight corticolous species of Haematomma are recognized in Australia, including four new species (H. eremaeum, H. pruinosum, H. sorediatum and H. stevensiae spp. nov.) and one new combination (H. infuscum). The characters found useful in differentiation of the species included apothecium form, apothecial pigmentation, spore septation, and thallus chemistry. Taxonomic and distributional data are provided for all species. Two taxa are reduced to synonymy for the first time, and a key is provided.

A method, including treatment with an enzyme/detergent mixture, of revealing features of the cortical hyphal arrangement in lichen thalli is described. The cortex structure of Parmelia saxatilis, Xanthoria parietina, Hypogymnia physodes and Lecanora muralis is illustrated and described.

The nomenclatural status of the 21 specific names in the British checklist affected by the abolition of later starting point dates for all fungi is discussed. Two are completely unchanged and the author citations of 15 are simplified by the deletion of previously ‘revalidating’ authors. Six alterations in name prove to be necessary: Microcalicium disseminatum (Ach.) Vainio for M. subpedicellatum (Schaerer) Tibell, Mycocalicium subtile (Pers.) Szat. for M. parietinum (Ach. ex Schaerer) D. Hawksw., Mycomicrothelia melanospora (Hepp) comb. nov. for M. atomaria (DC. ex Merat) Keissler, Opegrapha parasilica (Massal.) Vězda for O. persoonii (Ach. ex Gray) Chev., Orphniospora moriopsis (Massal.) comb. nov. for O. atrata (Sm.) Poelt, and Stenocybe pullatula (Ach.) B. Stein for S. byssacea (Fr.) Körber.

The typification of Ramalina leiodea (Nyl.) Nyl. is discussed; R. boninensis Asah. and R. boninensis f. subcalicariformis are considered to be conspecific with R. leiodea. A description of the taxon is given, and the morphological and chemical variability considered. The distribution of both the boninic acid and cryptochlorophaeic acid races is discussed.

Gaseous diffusion resistances for carbon dioxide and water vapour, thallus water content and thallus water potential were experimentally determined on species of the Stictaceae. The diffusion resistance to water loss was high only at low water contents and correlated closely with thallus water potential. Carbon dioxide diffusion resistances, however, were high at both low and high water contents and, even at medium water contents, were still an order of magnitude greater than the water resistance. These results indicate that carbon dioxide and water vapour exchange occur by different pathways in these lichens. Consequently it is suggested that the lichens have structural adaptations which separate the functions of water uptake, water storage and carbon dioxide exchange.

A cyclic exchange between communities of mosses and the lichen Baeomyces rufus is described. The cushions of different mosses are supplanted by the lichen. After a lifespan of about 3 years the lichen dies off and the location is repossessed by mosses. The vegetative reproduction of the lichen is adapted to this ecological cycle.

Twenty-five mainly crustose and saxicolous lichens are reported from the subalpine and alpine belts of Mt Changbai (n.-e. China, near the Korean border). All are new records to the lichen flora of the north-eastern provinces of China, 12 of them to the flora of all China, and four to the flora of all Asia. There is some floristic similarity to some other areas with cool humid climates in the Northern Hemisphere, e.g. Iceland.

Umbilicaria propagulifera (Vainio) Llano is reported as new to Poland. A morphological description is given and its distribution in both southern and northern hemispheres is established. U. vellea var. dendrophora is considered to be a synonym. The chemistry of U. propagulifera is variable. Its affinities within the genus and its possible relationship, as a species pair, with U. cylindrica are discussed.

The cryptogamic vegetation, dominated by lichens, in a secondary coastal dune area is described. The Coelocaulon aculeatum community colonizes large exposed sand patches. The Cladonia glauca–C. mitts community colonizes where litter has accumulated. The Cladonia mitis and C. portentosa communities occupy more sheltered sites than the Coelocaulon aculeatum community. The scattered Cladonia zopfii community colonizes both exposed and slightly more sheltered sand patches. The common Cladonia uncialis–C. mitis community usually colonizes smaller sand patches with some humus accumulation than those colonized by the Coelocaulon aculeatum community. The Cladonia mitis, the C. portentosa and the Cladonia uncialis–C. mitis communities and probably the Cladonia zopfii community are suggested to be final stages in the lichen succession.

Nylon mesh litter bags containing Parmelia caperata, P. flaventior, P. subrudecta, Evernia nesomorpha, Hypogymnia physodes and Umbilicaria muehlenbergii were placed on the floor of a black spruce bog in northern Minnesota to study the rates of decomposition. P. caperata and E. mesomorpha had decomposed after 10 months. Most of the lichens had completely decayed after 13 months but a few thalli of some species placed on top of hummocks were still alive. The species with usnic acid decayed as rapidly as those without. Lichens decompose rapidly but not more rapidly than some vascular plants.

The lichen flora of a very small, but outstandingly rich, outcrop of limestone and epidiorite at 1030 m in the Ben Alder range is described. One hundred and six calcicolous species were encountered, many of which are rare nationally; eight are not known elsewhere in Britain. The site is compared with other calcareous mountains in Scotland and possible reasons for its distinctive lichen flora are suggested.