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The lichen species Teloschistes lacunosus (RUPR.) SAV, and Ramalina bourgeana NYL. are characteristic of the semiarid southeast Iberian Peninsula. These species showing different distribution patterns and ecological requirements, were collected at the coast (R. bourgeana) and in the inland (T. lacunosus). Laboratory experiments revealed that net photosynthesis (NP) and dark respiration (DR) responses to temperature differed between both species. Optimal temperatures of NP were higher in T. lacunosus than in R. bourgeana at optimal thallus water content at the various photosynthetic photon flux density (PPFD) levels. In the upper temperature range studied (20-25 degrees C), R. bourgeana proved to be less efficient than T. lacunosus. In both species, lower and upper temperature compensation points were below 0 degrees C and above 30 degrees C, for moderate and high PPFD levels, respectively. At high temperatures and high thallus water content, T. lacunosus showed lower DR rates than R. bourgeana. NP response to PPFD also showed differences between both species. The light compensation points were high in both species for temperatures above 20 degrees C (at 20 degrees C around 50 mu mol m(-2)s(-1) in T. lacunosus, and around 60 mu mol m(-2)s(-1) in R. bourgeana). Light saturation of NP was higher in T. lacunosus at all temperatures in the experiments. In T. lacunosus, the value was below 1200 mu mol m(-2)s(-1) at 0-15 degrees C, but at temperatures above 15 degrees C, it was above 1200 mu mol m(-2)s(-1). In R. bourgeana the values were always below 1200 mu mol m(-2)s(-1). In both species, NP was strongly depressed at supraoptimal water content. The physiological differences observed between R. bourgeana and T. lacunosus, and their relation to the distribution patterns of these lichens are discussed.