The major works on British lichens published between 1724 and 1780 are briefly reviewed. The new lichens published in Withering's Botanical Arrangement of 1776 have been mostly overlooked; they were based on species described by Dillenius. These lichens are typified here, along with Withering's new lichens published in later editions of the Arrangement. Altogether 41 species are reviewed. The following 16 new combinations based on Withering's species are presented, with synonyms in parenthesis: Anaptychia runcinata (A.fusca), Caloplaca crenularia (C. festiva), Qadonia humilis (C. conista, C. conistea, C. conoidea), Qadoniapeziziformis (C. capitata), Cladonia ramulosa (C. anomaea, C. pityrea), Collema auriforme (C. auriculatum), Collema dichotomum (C. fluviatile), Collema fuscovirens (C. tuniforme), Dermatocarpon luridum (D. aqualicum, D. weberi), Leptogium gelatinosum (L. sinuatum), Lobaria virens (L. laetevirens), Peltigera didactyla (P. spuria), Peltigera lactucifolia (P. hymenina), Physconia distorta (P. pulverulacea), Ramalina lacera (if. duriaei), and Tornabea scutellifera (T. atlantica).

Later names affected by Withering's taxa are also investigated, and 12 are shown to be nomenclaturally superfluous. Other names are later homonyms, with the result that seven species require change of author citation as follows: Dactylina madreporiformis (Ach.) Tuck., Lecanora crenulata Hook., Psora lurida (Ach.) DC, Ramalina polymorpha (Liljeblad) Ach., Solorina spongiosa (Ach.) Anzi, Stereocaulon ramulosum Rauschel, and Sticta fuliginosa (Hoffm.) Ach.

The nomenclatures and systematic position of Cladonia conista C. Robb. ex Allen nom. illeg., Cliostomum griffuhii (Sm.) Coppins, Leptogium palmatum Mont., Lichen squamatus Dickson, Pachyphiale cornea (Ach.) Poetsch, and Pycnothelia papillaria Dufour is discussed, the correct name for Leptogium palmatum being L. corniculatum (Hoffm.) Minks and for Pachyphiale cornea being P. carneola (Ach.) Arnold. A history and account of Withering's herbarium is included.

A portable system for CO2 gas exchange measurements is described which allows determination of photosynthesis and respiration rates of lichens (and mosses) in the field under light, humidity and temperature conditions which are close to ambient. Time periods for enclosure of the thalli in a cuvette of this CO2-porometer for gas exchange measurement are shortened to between 1 and 2 min, so that an experimental influence on their water relations is small. Between the periods of gas exchange measurement, the lichens experience their natural microclimate conditions. Thus, measurements approximate closely the true gas exchange rates of the lichens under natural conditions. Diurnal courses of CO2 exchange of lichens found growing in a Mediterranean habitat in the spring are demonstrated, as determined by this method.

Cytological aspects of the mycobiont-phycobiont contact were investigated in the lichen species Peltigera aphthosa, Cladonia macrophylla, Cladonia caespiticia and Parmelia tiliacea by means of freeze-etch and thin sectioning techniques, and by replication of isolated fragments of myco- and phycobiont cell walls.

In the symbiotic state of the mycobionts investigated a thin outermost wall layer with a distinct pattern was observed mainly in the hyphae contacting phycobiont cells and in the upper medullary layer. No comparable structures were noted on the hyphal surface of the cultured mycobionts of the Cladonia and Parmelia species investigated. A distinct rodlet layer was found on the hyphal surface of the mycobiont of Peltigera aphthosa, while mycobionts of Cladonia macrophylla, C. caespiticia and Parmelia tiliacea had a mosaic of small, irregular ridges, each corresponding in its size to a bundle of rodlets on the outermost wall layer. Comparable surface layers have been described in aerial hyphae of a great number of non-lichenized fungi.

The rodlet layer of the mycobiont wall surface of Peltigera aphthosa adheres tightly to the outermost layer of the sporopollenin-containing cell wall of the Coccomyxa phycobiont. Mature trebouxioid phycobiont cells of the Cladonia and Parmelia species investigated in the symbiotic state had an outermost wall layer which was structurally indistinguishable from the tessellated surface layer of the mycobiont cells. A rodlet pattern was detected in the outermost wall layer of Trebouxia autospores still surrounded by the cellulosic mother cell wall. In mature Trebouxia cells the bundles of rodlets became increasingly covered by a homogeneous material, and thus attained the same tessellated pattern which was observed on the mycobiont wall surface. No comparable structures were found on the wall surface after culturing the Trebouxia phycobionts axenically in liquid media. Confluence of the tessellated surface layers of fungal and algal origin was noted at the contact sites of growing hyphal tips and young Trebouxia cells.

The possible correlations between these cytological features and published immunological data on the cell surface of cultured and symbiotic lichen myco- and phycobionts are discussed.

The contact sites of pycnidia and the terminal cells of trichogynes in Cladonia furcata were investigated using either freshly fixed material, or ascomatal primordia and pycnidia from which the gelatinous material either on the primordial surface, or in the pycnidial cavity, had been removed. The sickle-shaped conidia fused, tip first, with the cell wall of trichogynes. Circular holes of about the diameter of the conidia found in the cell walls of trichogynes arise from enzymatic degradation of the wall material by fusing conidia. As the conidia appear to stick on any gelatinous surface material of the thallus the adhesion process is presumed to be unspecific.

Notes and keys are provided for British members of the Trapeliaceae. The genus Placynthiella Gyelnik is resurrected to accommodate the Lecidea uliginosa group: P. hyporhoda (Th. Fr.) comb, nov., P. icmalea (Ach.) comb, nov., P. oligotropha (Laundon) comb. nov. and P. uliginosa (Schrader) comb. nov. Aphanopsis Nyl. ex P. Sydow is recognized for the single species A. coenosa (Ach.) comb, nov., and attention is drawn to the enigmatic Biatora humida Kullhem. The Lecidea granulosa group is referred to Trapeliopsis, necessitating four new combinations, T. aeneofusca (Flörke ex Flotow) comb, nov., T. flexuosa (Fr.) comb, nov., T. gelatinosa (Flörke) comb. nov. and T. viridescens (Schrader) comb, nov., and the description of one new species, T. pseudogranulosa sp. nov. Special attention is given to sorediate species of Trapelia, including T. corticola sp. nov. and T. placodioides sp. nov.

The lichen flora of hazel woodland on the island of Eigg off the west coast of Scotland is described. One area is interpreted as representing ancient ‘climax’ woodland partly on account of its rich epiphytic lichen flora. At other sites various levels of exploitation have modified the lichen communities. Site comparison has enabled a number of species to be recognised which may be useful in the recognition of relict hazel woodland in other oceanic areas. The ecology of the indicator species is discussed. Pertusaria alpina Hepp ex Ahles is reported as new to the British Isles.

The new species Placynthium arachnoideum Henssen is described from Patagonia. The lichen is characterized by incurved lobes retaining in part the false branching of the Scytonema phycobiont, and by two-celled, thick-walled spores with a perforated septum. Some localities in the Southern Hemisphere are given for P. asperellum, P. nigrum and P. subradiatum.

The cell wall composition of several species of the lichen phycobionts Trebouxia and Pseudotrebouxia has been investigated using gas chromatography, thin layer chromatography and infrared absorption spectrophotometry. In addition cell wall components (cellulose, non-cellulosic polysaccharides, sporopollenin, protein) were localized with cytochemical methods at the EM- level. The cell walls of Trebouxia and Pseudotrebouxia consist of several layers. In Trebouxia the inner layer (Si) consists mainly of cellulose, then followed by a non-cellulosic polysaccharide layer (S2), a sporopollenin-layer (S3) and an outer layer consisting again of a non-cellulosic polysaccharide (S4). In addition Trebouxia is surrounded by a sheath (a polysaccharide with species-specific terminal residues). In Pseudotrebouxia the cell wall is similarly constructed compared to Trebouxia, however, the sheath is lacking and the S4 layer contains a polysaccharide with species-specific terminal sugar residues. The role of the different cell wall constituents for the recognition mechanism between the lichen symbionts is discussed.

The rate of lobe division during thallus enlargement in Xanthoria elegans and Diploicia canescens is considered in geometric terms. The frequency of lobe engulfment by neighbouring lobes was measured, was fitted graphically to a simple equation and was found to result from constant lobe division with thallus size. Values for a constant in the equation and derived from the observed frequency of lobe engulfment provided a measurement of a new morphological parameter: ratio lobe length to width. Greatest departure from circularity in small thalli of D. canescens occurred when thallus size did not permit lobe competition. Increasing lobe engulfment and thallus circularity in larger thalli appeared to be correlated. Circularity in crustose thalli without lobes is discussed with definitions of ‘primary’ and ‘secondary’ areoles.

The lichen flora of natural outcrops, disused quarries and churchyards in the Magnesian Limestone belt of England, which stretches from Nottingham to Tyneside, is described with reference to 50 sites; 106 taxa were encountered. The lichen flora is compared with that of the Carboniferous Limestone in Derbyshire and found to be distinctive, relating particularly to the abundance of less exacting calcicoles. Lecanora campestris subsp. dolomitica, a lichen widespread at the southern end of the outcrop, is described.

The photosynthetic capacity changes that have previously been documented in lichens are reviewed together with the mechanisms of photosynthetic capacity change in free-living algae recently proposed by Prezelin and co-workers. Examination of seasonal capacity changes in Peltigera praetextata, P. rufescens, Cladonia rangiferina, C. stellaris, and Caloplaca trachyphylla using photosynthetic-illumination curves, provisionally establishes that synthesis of additional photosynthetic units, seasonal interruption of energy transduction, as well as enzymatic rate changes in the Calvin cycle, are all involved in these capacity changes.

Cyanobacteria symbiotic with 17 members of the Lichinaceae and Heppiaceae were brought into unialgal culture and their free-living characteristics examined. A diversity of cyanobacterial types was observed; this diversity was much greater than that reported in the literature. Both the in situ identification of cyanobionts and their role as an aid to the identification of these lichens are questioned.

Lecanora symmicta var. sorediosa Westman, a soraliate, yellow, crutose lichen frequently found on wood substrata along the sea shores in the arctic and boreal regions of the northern hemisphere, is now generally accepted as a distinct species, and has recently been provided with a new name: Lecanora arae-frigidae R. Sant. Besides usnic acid it contains zeorin, thiophanic acid and two accessory xanthones. The Finnish material of L. symmicta (Ach.) Ach. examined for comparison differs having thiophanic acid inconstant as well as three unknown substances, while lacking one of the xanthones. One specimen of L. orae-frigidae from the White Sea coast in Karelian A. S. S. R. was growing with a small thallus of Lecanora grantii Magnusson, a new record of the latter species for Europe.

Heavy metal uptake by lichens is briefly reviewed in terms of the trapping of paniculate material and the uptake of soluble cations. The kinetics of uptake to extracellular sites and intracellular carrier-mediated incorporation into cells are compared and the effects of competing cations and the energetics of the processes considered. The influence of heavy metals on lichen growth, morphology and physiology are reviewed emphasizing recent reports showing the greater sensitivity of cyanobacterial compared with chlorophycean lichens, the induction of heavy metal tolerance in the field and laboratory in Peltigera species, and alterations in intracellular cadmium uptake kinetics by some, but not all, tolerant Peltigera populations.

Peltularia crassa P. M. Jørg. & D. Galloway, a new, umbilicate lichen in the family Coccocarpiaceae is described from Campbell Island south of New Zealand. It occurs also on Macquarie Island. Its taxonomic and phytogeographical relationships are discussed.

Three name changes are proposed for the lichen checklist. Caloplaca heppiana should be called C. flavescens (Huds.)Laundon comb. nov. It is suggested that Coelocaulon muricatum (Ach.)Laundon comb. nov. is a more appropriate name for C. aculeatum subsp. hispidum. The name Schismatomma virgineum should be replaced with S. cretaceum (Hue)Laundon comb. nov.

The sensitivity of lichen species to air pollution was assessed by examining aspects of their rate of disappearance over a 5 year period in an area with rising SO2 concentration. These rates of disappearance were compared with the ecological index of species proposed by LeBlanc & DeSloover in 1970, i.e. the index of average number of neighbours for a given species. Linear correlation showed that this ecological index is a reasonably accurate indicator of species sensitivity. When the selection of species was performed according to criteria other than SO2 sensitivity, viz. according to the predilection of lichens for eutrophicated bark, the ecological index proved reliable only when trees whose conditions were non-optimal for this group were excluded. When applied to the group of species that avoids eutrophicated bark the ecological index proved most reliable, although the group of ‘ nitrophilous ’ species may also be used in air pollution indicator studies.

Investigation of two sites in the Caledonian allochthon of the central part of the Scandinavian peninsula has shown that several copper tolerant lichens occur on cupriferous substrates. Analysis of the thalli of two of these species, Acarospora rugulosa and Lecidea theiodes, using atomic absorption spectroscopy, X-ray diffraction, infrared spectroscopy and electron probe microanalysis has revealed that copper occurs at high concentrations (5% Cu dry weight) principally as crystals of copper oxalate (1–5 μm diam) encrusting the fungal hyphae within the medulla.