Plants: small to large, in tufts, mats, or sods, light to dark green or yellowish, sometimes reddish or glaucous, reddish brown proximally. Stems: 1–16(–20) cm, erect, simple, irregularly branched, or with a subfloral whorl of innovations, tomentose proximally. Leaves: with distalmost rarely spiraled around stem, stiffly erect to erect or erect-spreading, less commonly catenulate, erect to erect-spreading when dry, erect to spreading or occasionally secund when moist, lanceolate to broadly ovate-lanceolate or ovate-subulate, 0.6–3 mm; margins revolute, serrulate throughout, teeth paired, appearing 2-fid due to their apposing position from contiguous cells, sometimes margins plane, teeth unpaired; apex gradually to abruptly acute to acuminate, sometimes obtuse; costa short- to long-excurrent (often subpercurrent in obtuse leaves), 320 µm wide at base, distal abaxial surface smooth or weakly prorulose; laminal cells prorulose at proximal ends on abaxial side and at proximal and distal ends on adaxial side; basal cells rectangular to oblong-hexagonal, 15–30 × 5–8 µm; juxtacostal cells at widest part of leaf 24–40 µm; distal cells linear to oblong-linear, 15–40 × 3–5 µm. : Specialized asexual reproduction absent. Sexual: condition dioicous; perigonia discoid. Seta: 2–5(–7) cm, straight. Capsule: 1–3.5 mm. Spores: ovoid to reniform, 18–30 µm. North America, Mexico, Europe, Asia, Africa, Atlantic Islands (Iceland).
Varieties ca. 40 (3 in the flora). Philonotis fontana has a Holarctic distribution with limited penetration into the montane tropics of both Eastern and Western Hemispheres. The leaves are plane, 2- or pluriplicate, sometimes falcate or falcate-secund. Even given its membership in seepage communities, where morphological plasticity is not uncommon, the extent of variation in this species is excessive. Many variants have been recognized but with little firm evidence to support the majority of them. E. Nyholm (1954–1969) was convinced that only through a series of cultivation, cytological and genetic studies could the immense variability within this polymorphic complex be properly evaluated. W. M. Zales (1973) was able to show by a comparison of cultured and field-derived plants which of the morphological characters were relatively stable and which were subject to environmental influence. His treatment of this complex, with minor deviation, is followed here. The core characters for the species complex are laminal cells prorulose at proximal ends on the abaxial side, juxtacostal cells near the leaf base 24–40 µm, teeth of the leaf margin typically paired and appearing 2-fid, and costa 320 µm wide at the leaf base.
Plants: large. Stems: 5–16 cm. Leaves: with distalmost spiraled around stem, catenulate, spreading, distant, broadly ovate-lanceolate, sometimes falcate, pluriplicate. Capsule: 2.5–3.5 mm. Phenology: Capsules mature Jun–Sep.
Seeps, exposed slopes, mountain meadows. low to high elevations (0-3000 m). Alta., B.C., N.B., Ont., Que., Alaska, Calif., Colo., Idaho, N.Y., Oreg., Utah, Wash.
Variety americana, which includes the largest plants of the genus in North America, can be recognized by its robust habit, distant, catenulate leaves, and distalmost leaves spiraled around the stem.
Plants: small to large. Stems: 2–20 cm. Leaves: with distalmost not spiraled around stem, sometimes appressed, not catenulate, erect to spreading, imbricate, ovate-lanceolate, plane, or 2-plicate near base. Capsule: 2–3 mm. Phenology: Capsules mature year-round.
Rock, soil, seepy, open habitats. low to high elevations (0-3500 m). Greenland, Alta., B.C., Man., N.B., Nfld. and Labr., N.W.T., N.S., Nunavut, Ont., Que., Sask., Yukon, Ala., Alaska, Ariz., Calif., Colo., Fla., Ga., Idaho, Ill., Kans., Maine, Mich., Mo., Mont., Nebr., Nev., N.Mex., N.Y., N.C., Pa., S.C., S.Dak., Tenn., Tex., Utah, Vt., Va., Wash., Wyo., Mexico, c, w Europe, Asia, e, n Africa.
While the breadth of variation in var. fontana is immense, crucial characters include the typically robust habit and imbricate, laxly erect, straight, falcate or secund leaves. Plants that are subject to prolonged periods of submersion may develop unusual morphology.
Plants: small. Stems: 1–6 cm. Leaves: with distalmost not spiraled around stem, stiffly erect, sometimes somewhat secund, crowded to distant, lanceolate, not plicate. Capsule: 1–2 mm. Phenology: Capsules mature Jun–Aug.
Seepage slopes, along creeks, clay, silt, intermixed with other bryophytes. low to high elevations (0-3300 m). Alta., B.C., Man., N.S., N.W.T., Nunavut, Ont., Que., Yukon, Alaska, Calif., Colo., Minn., Mont., Oreg., Tenn., Wash., Wyo., c, n Europe, c, sw Asia, Atlantic Islands (Iceland).
Variety pumila is diminutive and typically grows in dense mats or sods; the stems are tightly interlaced with tomentum. The stiffly erect leaves that are neither catenulate nor spiraled aid in its identification. The range is arctic-alpine. This variety is a characteristic member of bog communities throughout the Arctic tundra and taiga.