Lendemer, J. C. & H. E. O'Brien 2011: How do you reconcile molecular and non-molecular datasets? A case study where new molecular data prompts a revision of Peltigera hydrothyria s.l. in North America and the recognition of two species. - Opuscula Philolichenum 9: 99-110. [RLL List # 223 / Rec.# 32916] Abstract: A revision of the aquatic macrolichen Peltigera hydrothyria utilizing biogeographical, chemical, morphological, and ITS1, 5.8s, and ITS2 nrDNA sequence data is presented. Phylogenetic analyses of the molecular data revealed three strongly supported clades representing one cryptic and two non-cryptic taxa. The name P. hydrothyria is restricted to eastern North American populations while the allopatric chemically distinct populations from western North America are recognized as a distinct species, P. gowardii. Peltigera gowardii is circumscribed broadly to include two distinct phylogenetic entities. These findings illustrate the utility of characteristics such as geography and secondary chemistry in delimiting otherwise morphologically cryptic species when combined with molecular data.