This occurs mostly in the west-central Appalachians and Shawnee Hills, but with disjunctions elsewhere (FNA 2). In Ky. it usually grows in shade on rather dry rocky soils below sandstone cliffs. The sterile hybrid with lucidula (X bartleyi) is occasionally found in overlapping habitats (Cranfill 1980), and may be locally abundant (D. Dourson, pers. comm.). H. porophila (and allies across North America) differs from lucidulum as follows (FNA 2, W): leaves mostly 3-9 x 0.6-1.3 mm (versus 6-15 x 1-2.5 mm), lanceolate or oblanceolate (versus narrowly obovate), entire or with 1-3 low teeth (versus with 1-8 irregular teeth); stomates on both surfaces (versus only abaxial/below); spores 25-41 µm (versus 23-29 µm).