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Teloschistaceae is one of the largest lichen-forming fungal lineages, with more than one thousand species worldwide distributed, including areas with extreme environmental conditions, such as Antarctica. Two species of this family, Austroplaca hookeri and Rusavskia elegans were investigated with molecular, morphological, and anatomical data to understand their diversity patterns in maritime Antarctica. These species can be confounded in a superficial identification due to their apparent similarities in color, shape, size, and dispersal mode (spores). Sampling area included the King George Island (South Shetland Islands), James Ross Island, and the Antarctica Peninsula. New nuITS sequences revealed low divergence in A. hookeri (haplotypes with a maximum divergence of 0.8%) and high phylogenetic diversity in R. elegans (haplotypes with up to 5.5% of divergence distributed in three different lineages). The same pattern was found examining the morphological and anatomical features, with phenotypic uniformity in A. hookeri and several variations among the R. elegans specimens (such as the presence and location of the isidioid structures, the margin of the hymenial disc, and the parahimenial tissue thickness). The phenotypic variability found in R. elegans is not linked to the different nuITS lineages or to the geographic origin of the specimens analyzed. These patterns probably reflect the unique evolutionary history of each species and their different pathways in the colonization of Antarctica. [ABSTRACT FROM AUTHOR]