SYSTEMATICS OF LECANORA SUBGENUS PLACODIUM (LICHENIZED ASCOMYCOTINA) IN NORTH-AMERICA - AN OVERVIEW, WITH KEYS

This paper gives an overview and progress report on our studies of the systematics of Lecanora subg. Placodium in North America, with keys t o the major supraspecific groups and brief discussions of major specie s complexes. As presently delimited, Lecanora subgenus Placodium sensu Poelt is a convenient but unnatural group represented by at least 30 species in North America. Two new groups within subgenus Placodium are described: Lecanora section Arctoxanthae Ryan & Nash, and Lecanora se ction Petrasterion Poelt subsection Deserticola Ryan & Nash. Lecanora crustacea (Savicz) Zahlbr. is reported for the first time from North A merica (Alaska), and L. christoi W. Weber is treated as a variant of L . Phaedrophthalma Poelt, previously known only from central Asia. Cons iderable range extensions are also reported for Lecanora maxima Lynge (west to the Yukon), L. microbola Lamb (west to Alaska), and L. opinic onensis Brodo s.l. (west to Arizona and the Northwest Territories).