Mnium fontanum Hedwig
Plants small to robust, in light to dark green or yellowish green tufts, mats or sods, occasionally reddish or glaucous, typically reddish brown tomentose proximally. Stems 1--16 cm, erect, simple, irregularly branched or with a subfloral whorl of innovations. Leaves stiffly erect to erect or erect-spreading, less commonly catenulate, sometimes falcate or falcate secund, rarely distalmost leaves spiraled around stem, lanceolate to broadly ovate-lanceolate or ovate-subulate, plane, bi- or pluriplicate, 0.6--3 mm, gradually to abruptly narrowed to acumen, apex acute to acuminate, occasionally obtuse; margins revolute, serrulate throughout, teeth paired and appearing 2-fid due to their apposing position from contiguous cells, occasionally with margins plane and teeth unpaired; costa short- to long-excurrent (often subpercurrent in obtuse leaves), to 320 µm wide at base; laminal cells prorulose at proximal ends on abaxial side and at proximal and distal ends on adaxial side, distal cells linear to oblong-linear, 15--40 × 3--5 µm, basal cells more lax, rectangular to oblong-hexagonal, up to 24--40 × 7--10 µm near costa. Sexual condition dioicous; perigonia discoid. Seta straight, 2--5(--7) cm. Capsule globose to ovoid, 1--3.5 mm. Spores ovoid to reniform, 18--30 µm, papillose.
Capsules mature throughout the year, with the season of maturation influenced by, among other things, latitude and elevation. Rock or soil, often in seepy, open habitats; 0--3500 m; Greenland; widespread in North America from Alaska to Mexico; c and w Europe; Asia; c and n Africa.
Philonotis fontana has a Holarctic distribution with limited penetration into the montane tropics of both Eastern and Western Hemispheres. Even given its membership in a seepage community, 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) 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 ("ecophenic characters"). His treatment of this complex, with minor deviation, is followed here. The core characters for the 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 up to 320 µm wide at the leaf base.