Plants glaucous-green. Stem leaves distant, loosely erect to wide-spreading; about 0.4--0.6 mm, ovate, long-apiculate to slenderly acuminate; margins irregularly dentate to spinose-dentate; distal laminal cells strongly papillose, each cell with a single, high, central papilla.

Mesic, calcareous rock crevices; B.C., N.B., Nfld., N.W.T., N.S., Nunavut, Ont., Que., Yukon; Alaska, Ark., Ill., Ind., Iowa, Ky., Maine, Md., Mich., Minn., Mo., N.H., N.J., N.Y., N.C., Ohio, Pa., S.C., Tenn., Vt., Va., W.Va., Wis.; Europe; n Asia.

This species is not uncommon in the East, but becomes rare in northwestern North America. Small, slender, glaucous plants with widely spaced leaves and very large papillae distinguish this species. The leaves end in a rather long, slender apiculus and the margins are distinctly and irregularly serrulate. The large central papillae and strongly toothed leaf margins distinguish this species from the two other species of the genus.