Hypnum rutabulum var. campestre Müller Hal., Syn. Musc. Frond. 2: 368. 1851; Brachythecium calcareum Kindberg; B. leucoglaucum Müller Hal. & Kindberg

Plants medium-sized to large, in moderately dense mats, light green, yellow-green, or whitish stramineous. Stems to 7 cm, creeping, terete-foliate, irregularly pinnate, branches to 8 mm, straight to slightly curved, terete-foliate. Stem leaves erect, loosely appressed, loosely imbricate, narrowly ovate-triangular or ovate-lanceolate, broadest at 1/9-1/7 leaf sometimes almost at costa insertion, concave, plicate, plicae usually parallel in falcate leaves, often shallow and uneven in straight leaves, giving some leaves a crumply appearance, 1.5-2.6 × 0.5-1.2 mm; base rounded, broadly short-decurrent; margins partly plane, recurved in many places, serrulate to serrate in acumen, occasionally almost entire, variable within one shoot; apex gradually tapered or acuminate; costa to 40-70% leaf length, moderately strong, small terminal tooth sometimes present; alar cells subquadrate or short-rectangular, same size as or smaller than basal cells, 15-25 11-13 µm, walls thick, region ± clearly delimited, 4-9 4-7 cells; laminal cells linear, (30-)60-100(-110) × 6-9µm; basal cells to 20-40 × 10-15 µm, region in 1-3 rows, . Branch leaves often falcate-secund; alar region conspicuous, pellucid, triangular. Sexual condition autoicous. Seta orange-brown to dark brown with age, 2-2.5 cm, rough or occasionally smooth. Capsule inclined to horizontal, dark brown, elongate, curved, 2 mm; annulus separating by fragments; operculum conic. Spores 15-19 µm.

Soil, wooded areas, limestone, concrete blocks, tree trunks; low to moderate elevations (10-500 m); Man., N.B., Nfld. and Labr. (Nfld.), N.S., Ont., Sask.; Conn., Del., Iowa, Maine, Mich., Minn., Mo., N.H., N.Y., R.I., S.Dak., Wis.; Eurasia.

A. J. Grout (1928-1940, vol. 3) and H. A. Crum and L. E. Anderson (1981) expressed some doubts on the status of Brachythecium campestre and its clear differentiation from B. salebrosum. However, B. salebrosum seems absent or at least rare in eastern North America (except probably the more northern regions of eastern Canada). The vast majority of collections referred to B. salebrosum in eastern North America belong to B. acutum, B. campestre, B. rotaeanum, and other species. There are some differences between European and American B. campestre; if further studies provide additional evidence for their separation, then the American populations should be called B. leucoglaucum; for typification of this name and discussion on this species, see M. S. Ignatov et al. (2008). The diagnostic characters of B. campestre include the usually light green to whitish color, ovate-lanceolate leaves that are rather crumply plicate when optimally developed, alar cells in small to large groups of rather small and subquadrate cells, and, usually, a minutely rough seta.