Bryol. Univ. 1: 183. 1826,.
Plants in hoary, dense tufts, dark green to dark-brown. Stems 0.5–2 cm. Leaves oblong-ovate to oblong-lanceolate, 1.5–3 × 0.4–0.6 mm, both margins plane, intermarginal bands absent, awn 0.3–2 mm, decurrent, broadly attached, acute, costa broad proximally; basal juxtacostal laminal cells elongate, straight, thick lateral walls, green; basal marginal laminal cells oblate to quadrate, straight, thick transverse and thin lateral walls, green, not hyaline; medial laminal cells roundedquadrate, straight, thick-walled; distal laminal cells 2-stratose, quadrate, thick-walled. Perichaetial leaves not enlarged. Seta straight, 1.5–3 mm. Capsule occasionally present, exserted, brown, oblong-ovoid to cylindric, exothecial cells quadrate, thick-walled, stomata present, annulus of 2–3 rows of rectangular, thick-walled cells, operculum short rostrate, peristome irregularly perforate distally, irregularly split. Calyptra mitrate.
Habitat: Humid to dry, exposed, acidic, sandstone and granite and basalt, open plains to montane, rarely alpine
Elevation: moderate to high elevations (200-2800 m)
B.C., Ala., Ariz., Ark., Calif., Colo., D.C., Fla., Ga., Idaho, Ill., Ind., Iowa, Kans., Ky., Md., Mass., Minn., Mo., Mont., Nebr., Nev., N.J., N.Mex., N.Y., N.C., Okla., Oreg., Pa., S.C., S.Dak., Tenn., Tex., Utah, Vt., Va., Wash., Wyo., Mexico, South America, Eurasia, Africa, Indian Ocean Islands, Australia
Grimmia laevigata is widespread and relatively common on the southern Great Plains, into the Ozarks, and along the Appalachians from northeastern Alabama to New England. There is also an extensive outlier in southern Minnesota and adjacent states. In western North America, it is abundant in California and the Pacific Northwest region into south central British Columbia. Although it occurs in the Rocky Mountain region it is not common there, being found mostly in lower elevation sites and along the east slopes. With the exception of a few disjunct sites in southern Georgia and Florida, it is unknown from the coastal plains of the American southeast. This is probably related to the extensive cover of calcareous Cretaceous and more recent bedrock. The northern limit of G. laevigata suggests a distribution influenced by the winter position of the Arctic airmass. Although known from high elevations, it is most often found below treeline on granite and acidic sandstones. It is an early successional invader of granitic rocks in the southeastern piedmont (H. J. Oosting and L. E. Anderson 1937, 1939; C. Keever et al. 1951). Classic specimens of G. laevigata are recognized by their broad leaves with almost no shoulder separating the proximal and distal lamina, and by their robust, broadly attached and long-decurrent awns. However, G. laevigata is quite variable with respect to leaf shape and awn attachment, with some specimens having bases approaching ovate and then often with rather narrowly attached awns. These specimens may be assigned to G. laevigata by the wide costa and oblate to quadrate basal marginal cells. Sterile specimens may be separated from G. crinitoleucophaea by the wide costa and thick-walled basal cells.
"thin" is not a number. "thick" is not a number.