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Summary• The cyanobionts of lichens and free-living Nostoc strains from Livingston Island (maritime Antarctica) were examined to determine both the cyanobiont specificity of lichens and the spatial distribution of Nostoc strains under extreme environmental conditions.• We collected five different lichen species with cyanobacteria as primary or secondary photobiont ( Massalongia carnosa , Leptogium puberulum , Psoroma cinnamomeum , Placopsis parellina and Placopsis contortuplicata ) and free-living cyanobacteria from different sample sites and analysed them using the tRNA Leu (UAA) intron as a genetic marker to identify the cyanobacterial strains.• Our results showed that the same Nostoc strain was shared by all five lichen species and that an additional strain was present in two of the lichens. Both Nostoc strains associated with lichen fungi also occurred free-living in their surrounding. Bi-and tri-partite lichens were not different in their cyanobiont selectivity.• Contrary to studies on different lichen species in temperate regions, the Antarctic lichen species here did not use species-specific cyanobionts; this could be because of a selection pressure in this extreme environment. Limiting factors under these ecological conditions favor more versatile mycobionts. This results in selection against photobiont specificity, a selection pressure that may be more important for lichen distribution than the effect of cold temperatures on metabolism.

The phylogeny of usneoid lichens with black pigmentation in the cortex was reconstructed using Bayesian and maximum parsimony analyses of nuclear ITS rDNA sequences. Fifty new partial sequences of 14 taxa were generated and assembled with 74 sequences from GenBank. Our results indicate that Neuropogon is polyphyletic with a core group nested within Usnea subgen. Usnea as sister–group to section Usnea. In addition an undescribed species is basal to the section Usnea clade and the Neuropogon species U. acanthella and U. durietzii have unresolved relationships in the Usnea subgen. Usnea clade. Monophyly of Neuropogon not nested within Usnea subgen. Usnea is rejected using three independent tests. Consequently, it is proposed to synonymise Neuropogon with Usnea. We recommend a conservative approach regarding nomenclatural changes from phylogenetic studies especially at the generic level when few taxa are studied.