The new species Ochrolechia splendens Lumbsch and Messuti, is described from Mexico, south-western North America, where it occurs on exposed siliceous rocks. It is characterized by relatively large apothecia with entire margins, the presence of the gyrophoric acid chemosyndrome in the thallus and apothecial disc and the presence of lichexanthone as major components.

Hydrogen sulphide emission in lichens as a response to low concentration SO2 fumigation was investigated. In an open flow-through system several lichen species were fumigated with 36 ppb SO2. Two species were also fumigated with higher concentrations (72, 119, 122 and 198 ppb SO2). Hydrogen sulphide emission was monitored concurrently by cryogenic trapping and analysis with gas chromatography. All tested species increased H2S emission significantly in response to fumigation with 36 ppb SO2. Parmelina tiliacea (L.) Hale and Cladina rangiferina (L.) Wigg. released significantly more H2S (0·098±0·015 and 0·073±0·013 pmol H2S g−1 d. wt s−1, respectively) than Parmelina quercina (Ach.) Hale, Ramalina menziesii Tayl. and Parmelia sulcata Tayl. (0·028±0·01, 0·025±0·014 and 0·023±0·013 pmol H2S g−1 d. wt s−1, respectively). Release of H2S in Hypogymnia physodes was enhanced by increasing SO2 concentrations up to 72 ppb SO2. No significant difference in H2S emission in the dark vs. in the light was found. Generally, no correlation was found between photosynthetic activity and H2S emission for the tested species. Uptake of SO2 was similar for all species, at 24·7±5·6 pmol SO2 g−1 d. wt s−1 in 36 ppb SO2 and increasing at greater SO2 concentrations. Therefore, H2S-S release represents only 0·11–0·74% of SO2-S uptake.

In two open, flow-through systems 11 lichen species were fumigated with concentrations between 0·036 and 2·0 ppm (c. 94·3–5240 μg m−3) SO2. Sulphur dioxide uptake was monitored concurrently as a mass balance between incoming and outgoing SO2 concentrations. The rate of uptake ranged from 0·025 (±0·006) to 0·7 (±0·16) nmol SO2 g−1 d. wt s−1, for all species. After the first hour of fumigation the uptake rate was almost constant during the following 5 h for concentrations up to 1·0 ppm SO2. At higher concentrations the uptake declined over time continuously. Within the range of measured SO2 concentrations the uptake rate was linearly correlated with SO2 concentrations (r2=0·90). Thalli which were killed by heat treatment or in which respiration was inhibited by azide treatment did not show significantly different SO2 uptake from living thalli. No differences in uptake were found during fumigation in the light versus in the dark.

For experiments run at 350 ppm CO2, the subtropical lichen Coenogonium does not exhibit net photosynthetic depression at water contents above those at which initial maximal values are reached. This is in contrast to most lichens for which such a depression occurs. We infer that the results reflect the unusual morphology of Coenogomum, in which the alga is the dominant symbiont, occurring as filaments at the lichen surface. This arrangement should minimize CO2 diffusion resistance to the algal surface. With light saturation occurring by 70 μmol photons m−2 s−1, Coenogoniium has one of the lowest light saturation values reported among lichens.

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.

The new species Peltula sonorensis is described from the Sonoran Desert. It is found in several localities throughout the Mexican part of the Sonoran Desert and belongs to a distinct group within the genus Peltula, which is characterized by fairly large (up to 15 mm diam.), umbilicate-peltate squamules, growing individually and having ellipsoid to bacilliform spores.

The status of four umbilicate lichens with lecanorine apothecia and hyaline, 1-celled ascospores is reviewed. It is concluded that Omphalodium should be emended to exclude O. arizonicum and consequently a new genus Omphalora T. Nash & Hafellner is proposed. Differences in anatomy, morphology, pseudocyphellae type, pigmentation and cell wall chemistry, and ascal dehiscence provide the primary justification for the new genus.