Growth strategy and the gradual symbiotic interactions of the Lichen Ochrolechia frigida

The symbiotic interactions in connection with the growth strategy of the cr ustose lichen Ochrolechia frigida (Sw.) Lynge have been investigated and th e flexibility of its life strategies is discussed. The lichen is an interes ting model organism for the mutualistic adaptation of bionts to each other and to the habitat conditions. O. frigida consists of verruciform granules which contain both bionts, and spinules and an extensive prothallus which b oth generally contain no algae. The algal-free stages seem to be capable of saprotrophic nutrition and hyphae penetrate cells and tissues of mosses, p hanerogams and lichens. A variety of morphological and anatomical adaptatio ns and a special type of reproductive biology are necessary to survive in h arsh environments. But the overwhelming success of O. frigida is based part ly on the capability of the algal-free mycobiont to colonize all plant subs trates and its ability to use parasitic or at least saprotrophic ways of li fe to supplement its symbiotic nutrition. The environmental conditions obvi ously influence the growth form of the lichen. In habitats where the biomat ter turnover is notoriously slow (e.g., in the Antarctic) saprotrophic nutr ition will be limited and the lichen is mainly characterized by granules.