Lichen-forming fungus Peltigera praetextata (Sommerf.) Zopf growing on mosses in northern Poland. The thallus of this common bipartite lichen contains the cyanobacterium Nostoc, which is frequently present, sometimes in addition to a green algal photobiont, in tripartite peltigeralean lichens. Small squamules (phyllidia) on the thallus surface are asexual propagules containing both symbionts (fungus and Nostoc). Pale brown, saddle-shaped fruit bodies (apothecia) contain sexual propagules (ascospores) of the mycobiont. A new classification for peltigeralean lichens is established here based on a comprehensive molecular phylogenetic study.