| As presently delimited, Lecanora subg. Placodium (Pers. emend. Poelt) Poelt is represented by at least 30 species in North America. This study focuses primarily on new or previously little-known species mainly in sections Endochloris, Dactylon and Petrasterion. Five new species are described: L. beamanii Ryan, L. pachysoma Ryan & Poelt, L. sonorae Ryan & Nash, and L. xanthosora Ryan and Poelt, all from Mexico, and L. weberi Ryan, from Colorado. Five new records for the continent are reported: L. albula (Nyl.) Hue, L. crustacea (Savicz) Zahlbr., L. dispersoareolata (Schaerer) Lamy, L. laatokkaensis (Rasanen) Poelt, and Squamarina degelii Poelt. Lecanora christoi W. Weber is a synonym of L. phaedrophthalma Poelt from Nepal. New data on chemistry, distribution, and variability are presented for several taxa, especially L. bipruinosa Fink, L. mellea W. Weber, L. novomexicana Magnusson, L. opiniconensis Brodo, L. phaedrophthalma Poelt, L. phryganitis Tuck., L. pinguis Tuck., L. semitensis (Tuck.) Zahlbr., and L. valesiaca (Mull. Arg.) Stizenb. Major secondary metabolic substances partially useful in classifying the taxa are usnic acids, triterpenes, fatty acids, depsidones and xanthones. Subgenus Placodium is compared with the genera Rhizoplaca Zopf and Squamarina Poelt, and with some of the presumed ancestral taxa (subg. Lecanora). Cladidium Hafellner, a genus recently segregated from Lecanora, is also treated, and the new combination Cladidium bolanderi (Tuck.) Ryan is made. |
