The distribution of many Arctic lichens is well known but their place and time of origin is still conjectural. Land bridges are often suggested but continental drift suggests a possible tie to Gondwanaland and Pangaea. This review suggests consideration of the available evidence for such ideas and emphasizes the need for more exact data from molecular studies of living and amber materials to determine the antiquity of the lichen species involved.

The northern and southern polar regions differ substantially in topography, climate, terrestrial habitats and in their biota. The Arctic flora comprises around 900 flowering plants, 600–700 bryophytes and 2000 lichens. The Antarctic flora is depauperate by comparison with only two flowering plants, 100–120 bryophytes, and probably only around 200 lichens. Despite considerable taxonomic uncertainty, broad phytogeographic patterns can be outlined, with species having a Maritime Antarctic, Peninsula and Lesser Antarctic, Circum-Antarctic, and Disjunct distribution pattern. The extent of endemism in the flora is unclear. The origin of the Antarctic lichen flora appears ancient in pan, although there is ample evidence for post-Pleistocene or Holocene colonization and invasion.

The climate, geology and vegetation of Tasmania's South West wilderness are described briefly, with particular reference to lichens. One hundred and sixty-two lichens are recorded from alpine altitudes in the region and the major habitats for alpine lichens are discussed. The flora differs significantly from that of other Tasmanian mountain systems, and this is attributed in part to geology and macroclimate. The region is rich in Tasmanian endemics and distinctly austral species with restricted geographical distributions.

The lichen flora and habitats in the Syowa region of continental Antarctica were surveyed. The distribution patterns of lichens appear to reflect habitat salinity, derived from wind-blown sea spray. Some halotolerant species are established in saline habitats where snow dunes are well developed. Snow and ice ameliorate the salinity of the habitat and provide a major source of moisture for lichens. Wind-borne drift snow carried by katabatic winds or occasional snow showers also provide the source of moisture to lichens growing on dry rock habitats in the Syowa region.

Extensive material of Caloplacafrom Arctic and Antarctic regions has been critically examined. A list of 49 species is presented for Arctic regions. They are presumed to have a more or less circumpolar distribution. Twenty-two species are listed from the Antarctic region, but about ten more, probably undescribed species, are present there. About one-third of the species in the Antarctic region are bipolar or widespread in cold regions; these include mainly terricolous and muscicolous species and none of them are maritime. It is assumed that migration of the bipolar or cosmopolitan species has taken place along the Andean mountain chain, whereas the maritime polar species have evolved separately in the two hemispheres. The Caloplaca species of the Antarctic region are provisionally assigned to the following distribution types: continental Antarctic, western Antarctic, insul-Antarctic and sub-Antarctic. Caloplaca exsecuta, C. saxicola and C. phaeocarpella are recorded as new to the Antarctic region. Caloplaca johnstonii (Dodge) Søchting & Olech, comb, nov., is established as the correct name of C. tenuis Øvstedal.

Three long-term studies of lichen growth and colonization have been undertaken at Signy Island, South Orkney Islands, in the maritime Antarctic. Small individual thalli of several crustose species and uncolonized plots on 12 fresh rock surfaces were photographically monitored at intervals of 3–4 years over a period of up to 20 years. The development of Ochrolechia frigida colonies on a regenerating moss bank, recently uncovered by a receding glacier, was similarly monitored. The results indicate that many lichens growing in sites enriched by nitrogenous compounds derived from populations of sea birds, have relatively rapid colonization and growth rates. Mean percentage increase in thallus area can be as high as 15–32% per annum in some nitrophilous saxicolous species (e.g. Acarospora macrocyclos, Xanthoria elegans and species of Buellia and Caloplaca), but as low as, 0·4–4% in nitrophobous species (Lecanora physciella, Lecidea sp., Rhizocarpon geographicum). Umbilicaria antarctica and Usnea Antarctica also yielded data indicating high growth rates, with colonist plants reaching several centimetres after 20 years. Colonization by mixed assemblages of lichens of new rock surfaces can attain 40->90% cover after 20 years in nutrient-enriched sites, and even 20–25% in non-biotically influenced sites. Colonization by or increase in extant O. frigida on the regenerating moribund moss bank was also quite rapid. It is suggested that the exceptionally large thalli of several lichen species and the locally extensive dense lichen fellfield communities in the maritime Antarctic may be much younger than previously supposed.

The stages of vegetation development close to two glacier fronts on two of the South Shetland Islands (Livingston and Robert) within the Maritime Antarctic were studied with special reference to saxicolous lichens. A lichenometric study of the crustose lichen Caloplaca sublobulata was carried out at both sites. On the moraine of Livingston Island, rock size played an important role in lichen development, explaining most of the differences observed in the diameter of C. sublobulata, the number of species, and the percentage of cover among the rocks studied. On Robert Island, the distance from the glacier front was associated with the lichen cover of the rocks but not with diameter of C. sublobulata This homogeneous distribution of C. sublobulata thallus size on the Robert Island study area points to a simultaneous recolonization of the whole zone by this lichen. The lichen development in the area studied on Robert Island seems to have been drastically affected by fluctuations in the persistence of snow cover following glacier front retreat. Tentative associations between ice retreat and colonization, on the o e hand, and changes in snow cover duration and the dynamic processes of extinction and recolonization, on the other, are suggested from comparison of the two zones.

This paper describes two versions of a new method for detecting and examining spatial pattern in communities of crustose saxicolous lichens. One version is based only on the shapes of the lichen thalli and the second on the identity of their species. These methods are useful for examining the spatial structure of a lichen community for the presence of anisotropy, the phenomenon of having different scales of pattern in different directions. If present, the nature of the anisotropy has implications for our understanding of the processes that give rise to spatial pattern. Preliminary results from communities in the Canadian Rockies suggest that while individual species show some evidence of anisotropy, when all species are considered together, or when only the shapes of the thalli and their boundaries are considered, anisotropy is reduced or absent.

Lichens dominate the terrestrial vegetation of the ice-free regions of continental Antarctica. Vegetation patterns were studied in the Windmill Islands Oasis, Wilkes Land, continental Antarctica, in relation to edaphic features to elucidate the factors that govern lichen distribution and abundance. Vegetation was studied on a low rounded knoll on Clark Peninsula some 3 km North East of the present Casey station. Substratum nutrient levels vary considerably across the knoll due to the presence of an abandoned penguin rookery on the crest and the uneven topography provides both sheltered and exposed sites. Along a 130 m-long transect crossing the knoll from South to North, a total of 25 species of lichen and one moss were identified, the vegetation being dominated by Umbilicaria decussata, Pseudephebe minuscula, Usnea sphacelata and U. antarctica. TWINSPAN analysis of species distributions identified six sociations, the distribution of which were related to substratum structure and chemistry. Several species were restricted to nutrient-rich zones while late-lying snow restricted all species to varying degrees.

Five populations of the circumpolar Arctic-alpine lichen species Cetraria nivalis were sampled along a latitudinal gradient from the temperate to the Arctic climatic zone. The populations were compared with respect to their CO2 exchange, water relations and morphology/anatomy. Provenances from places along this latitudinal gradient were transplanted in 1983/84 to a site near the Scientific Research Station in Abisko, to see whether they are identical with plastic acclimation ability or whether they represent different ecotypes. The five populations represent two major geographical groups, a ‘southern’ and a ‘northern’ one, with respect to some morphological and anatomical features, chlorophyll content and water relations. The transplanted C. nivalis provenances showed a tendency towards increasing net photosynthetic rates with origin in the higher latitudes. The CO2 exchange response of the native populations was the reverse of this tendency although CO2 exchange was in general flexible. It is concluded that the investigated C. nivalis populations were different ecotypes because of genetic differences and a distinct seasonal plasticity. The ecotypes are interpreted as a result of isolation in different refugia during the Pleistocene.

Primary production in lichens, as in all plants, is the result of gains and losses. Losses of carbon may be high under extreme environmental conditions. In the harsh climate of polar regions lichens use much carbon for maintenance and in their stress response. Thallus biomass is preserved through periods of darkness, extremely low temperatures and snow cover. On the other hand, lichens are photosynthetically active at temperatures below 0°C. They can make use of melted water from snow and ice and take up water vapour from snow. Physiological adaptations and environmental conditions under which growth is possible are discussed in terms of our recent results. A concept model describes the main parameters that influence carbon acquisition, growth and water relations of lichens in polar regions.

Interaction effects of UV-B and CO2 on three lichens species, Cladonia arbuscula, Cetraria islandica and Stereocaulon paschale, from two latitudinal sites, 68°N and 56°N, were studied in a laboratory experiment. The response of the plants was recorded by measuring their chlorophyll fluorescence. All species had a similar response to enhanced UV-B depending on the latitude from which the population came and the time of the season when they were sampled. Overall, there was a significant increase in photosystem II yield (as measured by a fluorescence technique) due to UV-B and no separate effect due to enhanced CO2, although there was a significant interaction between CO⊂2 and UV-B. The increase due to UV-B was at the low CO2 level. There were also significant differences in response due to latitude. The results contradict our hypotheses that negative effects of UV-B would be larger in the North than in the South and that a negative response hould be especially large during the early season.

Under field conditions of optimal water hydration, lichen photosynthesis is primarily light-limited and nitrogen fixation is temperature-limited in both Peltigera canina and Stereocaulon tomentosum at Anaktuvuk Pass, Alaska. Thus, where duration of optimal hydration conditions remains unchanged from the present-day climate, the anticipated temperature increases in the Arctic may enhance nitrogen fixation in these lichens more than carbon gain. Because nitrogen frequently limits productivity in Arctic ecosystems, the results are potentially important to the many Arctic and subarctic ecosystems in which such lichens are abundant.