Imshaugia aleurites
Imshaugia aleurites photo by Ray Showman
DIAGNOSTIC FEATURES: Often rather randomly arranged thallus; isidia covering most of surface, massing towards center; gray-white appearance; cortex, K+ quickly yellow (thamnolic acid); compare with Heterodermia granulifera which has isidia granular to papillate or pustulate, medulla K+ red, and with Parmelia squarrosa and Parmelinopsis minarum which have undersurface black.
ECOLOGY: Widely distributed in the mountainous parts of the US; mainly eastern in Ohio on conifer or deciduous bark or old wood; prefers ridgetops or dry locations.