Background and aims – Algae living in low pH environments have been the subject of numerous studies, but their phylogenetic relationships with relatives found in non-acidic habitats are poorly known. In the present study we analyzed the morphology and phylogeny of acid-adapted strains of Klebsormidium, a genus of filamentous green algae frequently present in low pH environments. Methods – Eighteen strains of Klebsormidium were collected from from low pH habitats in Europe and U.S.A., mainly from terrestrial sites affected directly or indirectly by carbon mining activities. These algae were isolated in culture and their phylogenetic relationships were studied using rbc L and ITS rDNA sequence data in a concatenated dataset. Key results – In the molecular phylogeny the strains of Klebsormidium living in low pH habitats formed a polyphyletic assemblage. They were representative of sixteen lineages and corresponded morphologically to six species ( K. crenulatum, K. elegans, K. flaccidum, K. fluitans, K. nitens, K. scopulinum ), with the exception of four strains for which an unambiguous identification was not possible. Conclusions – The genus Klebsormidium is a group of morphologically and physiologically dynamic algae in which the capacity of adaptation to low pH conditions has been developed multiple times independently. Extreme acidophilic populations probably originate from populations of various species growing locally when strongly acidic habitats become available. For the acid-adapted lineages of Klebsormidium examined here the current known distribution is geographically restricted, with the exception of a lineage containing strains from Czech Republic, New Zealand and Ohio.

ACID MINE DRAINAGE; ACIDOPHILIC ALGAE; ACIDOTOLERANT ALGAE; EXTREMOPHILES; KLEBSORMIDIALES; KLEBSORMIDIUM; MOLECULAR SYSTEMATICS; PHYLOGENY; STREPTOPHYTA; TAXONOMY