5. Polytrichastrum formosum (Hedwig) G. L. Smith, Mem. New York Bot. Gard. 21(3): 37. 1971.
Polytrichum formosum Hedwig, Sp. Musc. Frond., 92, plate 19, fig. 1a. 1801; P. attenuatum Menzies
Plants medium and slender to large and robust, green to dark olive green to blackish, in loose tufts. Stems (2-)3-8(-20) cm, mostly unbranched. Leaves 6-8(-12) mm, erect to erect-spreading when dry, spreading to subsquarrose and broadly recurved when moist; sheath ovate to elliptic, yellowish, hyaline-margined, gradually tapering or abruptly contracted to the blade, the cells at the shoulders forming a differentiated hinge; blade lanceolate to linear; costa prominent abaxially and toothed near the tip; excurrent as a short, toothed point; marginal lamina erect, (2-)3-5(-10) cells wide, plane or erect, sharply toothed from apex nearly to the sheath; lamellae (3-)4-5(-7) cells high, margins ± entire to finely serrulate in profile, the marginal cells in section rounded to narrowly elliptic and somewhat taller than the cells beneath, the cell walls not or moderately thickened; median cells of sheath 8-12 µm wide, narrowly rectangular, 5-7(-10):1; cells of marginal lamina subquadrate, 10-15 µm. Sexual condition dioicous or polygamous; perichaetial leaves similar to the foliage leaves, or somewhat longer, with a longer sheath. Seta 3-6 cm, yellowish to reddish brown. Capsule 4-7 mm, rather slender or short-rectangular, acutely 4(-6)-angled, inclined to almost horizontal, pale yellowish brown to brownish; hypophysis cylindric, indistinctly delimited or set off by a shallow groove; exothecium smooth or the cells weakly convex, quadrate to hexagonal, without a central thin spot; peristome 600 µm, divided to 0.6, the teeth 64 and highly regular in form or fewer and somewhat irregular, pale to brownish; epiphragm absent marginal teeth. Spores 12-16 µm.
Varieties 3 (2 in the flora): widespread, temperate to cool temperate latitudes in the Northern Hemisphere.
European treatments often assert a similarity between Polytrichastrum formosum and Polytrichum commune, which cannot be said of the North American expression of the species. The habitat and ecology of the European plants are also distinct: A. J. E. Smith (2004) described P. formosum in Britain as a common and weedy species of heaths, moorland, woods, outcrops, and old walls.