Lecanora insignis is a rarely reported species in the L. subfusca group, previously known only from montane forests in the southern Appalachians, European Alps, Himalayas and Taiwan. Here, we report its discovery in wet Thuja occidentalis forests at elevations of 50 to 300 m in eastern Canada and northern Maine, U.S.A., along with three associated lichenicolous fungi. Ascospore size is shown to clearly differentiate L. insignis from the similar L. cinereofusca. The lichenicolous species Skyttea insignis is described as new to science, differing from S. lecanorae in its longer ascospores, larger ascomata and apparent host specificity. It is the most frequently encountered lichenicolous fungus on L. insignis in northeastern North America, occurring in nearly half of the collections examined in this study. Stigmidium congestum was found at two localities, one in New Brunswick, Canada, and one in Maine; it is new to North America. Paranectria oropensis is new to eastern Canada.