Morphological, anatomical, and chemical studies have been made of the types of about 90% of the world's reported Phyllopsora species, of types in related genera, and of much non-type material, including specimens collected in recent years by the authors and other botanists in East Africa. The findings are reported, and on their basis an attempt is made to delimit the genus. A detailed account is given, with key, of the East African species. The following 11 species are reported for East Africa, three of them being newly described: Phyllopsora albicans Mull. Arg., P. breviuscula (Nyl.) Mull. Arg., P. buettneri (Mull. Arg.) Zahlbr., P. chlorophaea (Mull. Arg.) Zahlbr., P. confusa sp. nov., P. haemophaea (Nyl.) Mull. Arg., P. martinii sp. nov., P. mediocris sp. nov., P. pannosa Mull. Arg., P. santensis (Tuck.) comb, nov., P. thaleriza (Stirton) G. Schneider. In addition one species is reported as undetermined (Species A). The following taxa are reduced to synonymy: Phyllopsora porphyromelaena (Vainio) Zahlbr. and P. formosana Zahlbr. with P. albicans; P. brachyspora Mull. Arg. with P. breviuscula; P. subparvifolia (Mull. Arg.) Mull. Arg. and Lecidea schizophylla (Vainio) Malme with P. chlorophaea; P. kiiensis (Vainio) G. Schneider and Lecidea schizophylla var. isidiata Malme with P. haemophaea; P. miradorensis (Vainio) G. Schneider with P. santensis; Psora ochroxantha f. aelhiopica (Stizenb.) Dodge with P. thaleriza; Lecidea ernstiana Mull. Arg. with P. ochroxantha (Nyl.) Zahlbr.; P. melanocarpa Mull. Arg. with Neophyllis pachyphylla (Mull. Arg.) G. Schneider; P. schizophylloides (Malme) G. Schneider with P. munda (Malme) Zahlbr.; and P. spinulosa (Vainio) Zahlbr. with P. polydactyla (Mull. Arg.) Zahlbr. The following new names and combinations are made: Bacidia laciniosa nom. nov., B. spruceana (Mull. Arg.) comb, nov., Phyllopsora bibula (Taylor) comb, nov., P. glabriuscula (Nyl.) comb, nov., P. janeirensis (Mull. Arg.) comb, nov., P. microphyllina (Tuck, ex Nyl.) comb, nov., P. pertexta (Nyl.) comb, nov., P. pyrrhomelaena (Tuck.) comb, nov., and P. santensis (Tuck.) comb. nov.

The origin and development of pseudocyphellae and the pored epicortex are compared. Pseudocyphellae are pores through the paraplectenchymatous cortex which fill with medullary hyphae. The pored epicortex is a thin, perforated polysaccharide sheet lying over a loosely organized cortical layer. Both structures function in gas exchange and may represent two different phyletic lines.

The lichen genus Chrysothrix Mont, is shown to comprise four species: C. candelaris (L.) Laundon comb, nov., C. chlorina (Ach.) Laundon comb, nov., C. chrysophthalma (P. James) P. James & Laundon comb, nov., and C. pavonii (Fr.) Laundon comb. nov. (C. noli-tangere (Mont.) Mont.). The genera Pulveraria Ach. and Temnospora Massal. are placed in the synonymy of Chrysothrix nom. cons., and all bright yellow, leprose, sterile lichens with pulvinic acid derivatives, formerly included in Lepraria and Crocynia, are referred to the genus. Chrysothrix oceanica Rasanen is excluded; it probably belongs to Caloplaca. A key to and detailed accounts of the recognized species are included. There are three chemotypes of Chrysothrix candelaris, one of which is probably of hybrid origin.

Both light and scanning electron microscopy have been used to investigate the morphology and development of Speerschneidera euploca (Tuck.) Trevisan. This monotypic genus produces lecanoralean apothecia and Lecanora-type asci; the latter negates the assumed relationship to Teloschistes and the Teloschistaceae. The information on morphology, ecology, development and chemistry indicate that the genus is appropriately placed in the Lecanoraceae close to Lecania. S. euploca is found on calcareous outcrops from Missouri southwest to Texas and Mexico. It produces only a brown pigment concentrated in the tips of the paraphyses.

The citrine–green Candelariella flavovirella (Nyl.) Lettau and C. heidelbergensis (Nyl.) Poelt are shown to differ from the yellow-orange species C. vitellina (Hoffm.) Mull. Arg. and C. aurella (Hoffm.) Zahlbr. respectively, mainly in the suppression of calycin. As distinctive and geographically scattered chemotypes it is suggested that the rank of form is most appropriate and the required new combinations are made. A citrine–green population of C. medians (Nyl.) A. L. Sm. is described as f. steepholmensis O. Gilbert f.nov.

Lemmopsis is retained as a genus in the Lichinaceae. Three species are recognised, L. arnoldiana (Hepp) Zahlbr., L. oblongans (Nyl. ex Crombie) A. L. Sm. and L. pelodes (Körber ex B. Stein) comb. nov. Lemmopsis leptogiella (Nyl.) A. L. Sm. is transferred to Porocyphus. The status of Psorotichia flotowiana (Hepp) Müll.Arg. is discussed and its affinities suggested.

The new generic name Lichenothelia nom. nov. is introduced for the Microthelia aterrima group which proves to be unrelated to the corticolous mainly nonlichenized fungi generally referred to Microthelia. Two species are accepted, Lichenothelia metzleri (Lahm) comb. nov. and L. scopularia (Nyl.) comb. nov. [syn. M. aterrima (Krempelh. ex Anzi) Zahlbr.], distinguished by the ascospore size and septation, iodine reaction of the hymenial gelatin and ascus walls, and further the shape of the asci and extent of the development of the interascal filaments. The systematic position of the genus is unclear as the ascus structure shows affinities with both the Lecanorales and Dothideales. It is also uncertain whether it really should be regarded as lichenized.

The new genus Degelia (Pannariaceae) is described to accommodate three primarily Southern Hemisphere taxa: D. gayana (Mont.) comb, nov., D. duplomarginata (P. James & Henssen) comb, nov., and D. durietzii sp. nov. A key to the species is given, with data on synonymy, morphology, anatomy, chemistry, habitat and distribution. Coccocarpia gayana var. melacarpina Nyl. is reduced to synonymy with Degelia gayana. Relationships of Degelia with genera in the Pannariaceae and Coccocarpiaceae are discussed. Degelia is distinguished from other genera in the Pannariaceae by periclinal arrangement of cells in the upper cortex, a lower cortex of 2–3 layers of thick-walled periclinal hyphae, and Scytonema as the phycobiont; and from genera in the Coccocarpiaceae by the structure and ontogeny of the apothecia. D. duplomarginata is known from New Zealand and Hawaii, D. durietzii from New Zealand and Tasmania and D. gayana from New Zealand, Tasmania, Australia, Chile and Tristan da Cunha.

Wide north-south transplants were made with three lichen species, Parmelia cumberlandia, Cladonia turgida and Stereocaulon saxarile. The objective was to determine whether thallus chemistry would be altered due to wide geographic displacement of thallus segments from the control locations. Significant quantitative variation in microchemistry was observed among thalli of P. cumberlandia and among those of C. turgida, but there were no qualitative or quantitative effects on the lichen products, usnic acid, atranorin, constictic, stictic, norstictic, fumarprotocetraric and lobaric acids, due to transplantation.

The quantitative distribution of five lichen acids, including fumarprotocetraric acid, in seven specimens of Australian scyphose Cladonia species was determined by reverse phase high pressure liquid chromatography, using butylated hydroxy-toluene as internal standard. The highest concentrations of lichen acids were found in the scyphi and it is suggested that this localized distribution of lichen acids is due to repeated upward capillary flow, of saturated solutions of the acids, in the podetia followed by evaporation in the upper parts of the podetia.

A second fascicle of a lichen exsiccata containing species of Caliciales has been issued; 25 species from Europe and North America are included. Some remarks on their taxonomy, nomenclature and distribution are given here. Calicium queenslandiae (F. Wilson) Tibell, Chaenothecopsis nana Tibell, Chaenothecopsis vainioana (Nádv.) Tibell and Phaeocalicium polyporaeum (Nyl.) Tibell are discussed in some detail. Distributional records of interest are given for Calicium queenslandiae, Chaenothecopsis nana, C. subpusilla (Vainio) Tibell, C. vainoiana, C. viridialba (Krempelh.) A. Schmidt and Phaeocalicium polyporaeum.

Gyalectidium corticola sp. nov. is described from Costa Rica. It is the first corticolous lichen to be formally described in this primarily foliicolous genus. The structure of the ascocarps and their pattern of development is similar to the type species of the genus but it also shows some resemblance to other genera in the Asterothyriaceae in different features. Of particular note is the production of conidia within the massive muriform ascospores.

Fifteen species of the Caliciales are reported from Africa and Macaronesia. Calicium subquercinum, Chaenotheca chrysocephala, Ch. trichialis, Coniocybe furfuracea, C. gracillima, Sphinctrinella calicioides and Tylophoron protrudem are new to Africa; Calicium trabinellum and Strongyleuma exsertum are new to Macaronesia.

The species belong to two groups with respect to their distribution: (1) the borealtemperate species with a wide distribution in the Northern Hemisphere, such as Chaenotheca chrysocephala and Ch. trichialis, occur only at high elevations, usually about or above 3000 m; (2) one including, for example, Tylophoron moderatum, T. protrudens and Schistophoron—species occurring at low or moderately high elevations with a subtropical/tropical distribution.

Lichen growth is reviewed in the context of the anatomy of the growth region, thallus morphology of crustose and foliose lichens, photosynthesis, mathematical models and their application. The Aplin & Hill model is suggested as a basis for more detailed investigation of integrated processes of growth including not only the size increase but also the general structure of the thallus and the processes which limit growth.

The phycobionts of 20 different lichens were studied in culture, described and assigned to species of Pseudotrebouxia and Trebouxia. Identical phycobiont species were isolated from widely different lichens which showed that these algal symbionts were not specific to particular mycobionts. There was much variation in cellular detail within individual algal species indicating that the criteria currently used to separate species of these phycobionts may be too restrictive.

A study of the weathering phenomena brought about by the growth of Lecanora alra on a substrate of magnesium silicate minerals (serpentinite) has been carried out mainly by X-ray diffraction and scanning electron microscopy. The lichen thallus contains appreciable amounts of crystalline magnesium oxalate dihydrate, which occurs as an insoluble extra-cellular precipitate and derives from the decomposition of magnesium silicates (particularly chrysotile) by oxalic acid secreted by the mycobiont. In theory magnesium oxalate dihydrate should be capable of incorporating large amounts of heavy metal ions into its structure, as indeed the electron probe evidence indicates has happened, thus suggesting a mechanism for enabling some lichens to cope with environments that are high in these generally harmful ions. The only weathering product detected in the lichen weathering crust is an X-ray amorphous silica gel which often retains the fibrous morphology of the chrysotile from which it forms.

Lichen thallus fragments were maintained in a growth cabinet under four differing conditions of light intensity. Levels of usnic acid and atranorin did not differ significantly from the control under any of the treatments. However, perlatolic acid and fumarprotocetraric acid per unit dry weight of thallus were dependent upon light availability.

The value of terricolous lichens as bioindicators of industrial metal fallout patterns is investigated; the widely-known inverse relationship between the metal content of lichens, as well as their associated soils, and the distance from the pollution source was found to be affected by microclimatic factors dependent upon soil surface topography and the local vegetation. Samples of lichen vegetation and their associated soils from Risby Warren, North Lincolnshire, were analysed for Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn. Enhanced concentrations of Fe and Mn in the lichen, soil and air samples were indicative of their emission from the nearby Scunthorpe steelworks. The highest concentrations of all metals analysed were found to be in the top layer (0-5 cm) of the soils.