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.
