LECANORA SECT PETRASTERION (LICHENIZED ASCOMYCOTINA) IN NORTH-AMERICA- LECANORA-PUEBLAE SP-NOV, FROM MEXICO AND LECANORA-KOFAE SP-NOV, FROM ARIZONA

Two new species of Lecanora subg. Placodium sect. Petrasterion are des cribed from North America. Lecanora pueblae Ryan & Nash, sp. nov., fro m Puebla, Mexico, on limestone, is rather similar to L. sonorae Ryan & Nash in general appearance and also contains usnic and psoromic acids as the only lichen substances, but differs especially as follows: 1) thallus thinner, more appressed; 2) lobes narrower, more elongate, con tiguous, somewhat convex; 3) surface smooth, continuous, and somewhat glossy, with concolorous edges; 4) apothecial discs glossier, often re ddish brown; 5) occurrence on limestone rather than siliceous rock. Le canora kofae Ryan & Nash, sp. nov., from Arizona, is superficially som ewhat similar to Squamarina (Petroplaca) degelii Poelt and like that s pecies contains usnic and roccellic acids, but L. kofae has a more fla ttened and distinctly rosulate thallus with somewhat elongated margina l lobes, and has cortical hyphal bundles dividing the algal layer. Lec anora kofae also shows considerable similarities, in external appearan ce and in cortical structure, to forms of L. bipruinosa Fink, but (as in L. pueblae) has epruinose apothecial discs and differs in medullary chemistry. The two new species are of uncertain affinities within Pet rasterion, but they (and L. sonorae) may be closer to L. bipruinosa th an to other members of the section. This article is one of a series in which we deal with Lecanora subg. Placodium sect. Petrasterion Poelt in North America. Its purpose is to describe two new species which we feel are distinctive enough to warrant recognition, even though they a re presently known only from single or few collections. The two specie s are rather different from each other, and both are of uncertain affi nities within the section, but show at least some superficial similari ties to Lecanora bipruinosa Fink.