Many interesting ferns can be found growing on rocky outcrops, but one of my favorite common ferns has to be Dryopteris marginalis (Marginal Shield Fern).
Found flowing over the edges of sandstone outcrops and ledges as well as growing in the sandy soils of the dunes around the Great Lakes, Dryopteris marginalis is easily identified by the marginally-disposed sori, shown above. This fern is found throughout the eastern half of North America and Greenland, and is apparently also known from Brittish Columbia. I most recently saw this species on the north-facing sandstone ledges at Fall Creek Gorge in Warren County, Indiana. For more plant photos from my recent trip to Fall Creek Gorge, visit my post at Through Handlens and Binoculars.