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 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.

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.

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 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.