Identification of photobionts from the lichen family Physciaceae using algal-specific ITS rDNA sequencing

The identity of photobionts from 20 species of the Physciaceae from differe nt habitats and geographical regions has been determined by ITS rDNA sequen ce comparisons in order to estimate the diversity of photobionts within tha t lichen group, to detect patterns of specificity of mycobionts towards the ir photobionts and as a part of an ongoing study to investigate possible pa rallel cladogenesis of both symbionts. Algal-specific PCR primers have been used to determine the ITS rDNA sequences from DNA extractions of dried lic hens that were up to 5 years old. Direct comparisons and phylogenetic analy ses allowed the assignment of Physciaceae photobionts to four distinct clad es in the photobiont ITS rDNA phylogeny. The results indicate a diversity w ithin the genus Trebouxia Puymaly and Physciaceae photobionts that is highe r than expected on the basis of morphology alone. Physciaceae photobionts b elonged to 12 different ITS lineages of which nine could unambiguously be a ssigned to six morphospecies of Trebouxia. The identity of the remaining th ree sequences was not clarified; they may represent new species. Specificit y at the generic level was low as a whole range of photobiont species were found within a genus of Physciaceae and different ranges were detected. The photobionts of Physcia (Schreb.) Michaux were closely related and represen ted one morphospecies of Trebouxia, whereas the algal partners of Buellia D e Not and Rinodina (Ach.) S. Gray were in distant lineages of the ITS phylo geny and from several Trebouxia morphospecies. Photobiont variation within a genus of Physciaceae may be due to phylogeny, geographical distance or be cause photobionts from neighbouring lichens were taken ('algal sharing'). A t the species level Physciaceae mycobionts seem to be rather selective and contained photobionts that were very closely related within one morphospeci es of Trebouxia. (C) 2001 The British Lichen Society.