A very common fern of mortared stone and brick walls or of limestone or basalt rock outcrops. (Far commoner than the ssp. trichomanes, which is virtually absent from Northern Ireland except for one known site in the Mournes.)
All names: Asplenium trichomanes ssp. quadrivalens D.E.Mayer; Asplenium trichomanes ssp. quadrivalesns D.E.Meyer emend.Lovis