Mem. New York Bot. Gard.21(3): 35. 1971· [Genus Polytrichum and Latin -astrum, incomplete resemblance],
Widespread in temperate and boreal latitudes in Northern Hemisphere, scattered in the Southern Hemisphere.
Species ca. 20 (8 in the flora).
Species of Polytrichastrum have a peristome of the leiodont type (S. O. Lindberg 1868). The capsule is terete or obtusely (in fresh capsules) 4–6-angled, the apophysis tapering or short-cylindric but not sharply separated from the rest of the capsule by a deep basal constriction. The epiphragm is loosely attached and early deciduous. Capsules are pale greenish or yellowish brown rather than dark brown or purplish, and not glaucous when fresh as in Polytrichum. The exothecial cells are not bulging mammillose or pitted, but may have a diffuse thin spot on the outer wall. Spores are papillose rather than minutely echinulate as in Polytrichum. Polytrichastrum alpinum is distinct genetically from other members of the genus (G. S. Derda et al. 1999). Other Polytrichastrum species show evidence of allopolyploid origin, possibly involving interspecific or even intergeneric hybridization between species of Polytrichastrum and Polytrichum.
|1||Lamellae coarsely papillose; capsules terete, long-cylindric to ovate-cylindric to suborbicular||> 2|
|1||Lamellae not papillose (rarely faintly striate-papillose); capsules 4-6-angled||> 3|
|2||Lamellae margins entire in profile; exothecial cells without thin spot.||Polytrichastrum alpinum|
|2||Lamellae margins crenate in profile, the marginal cells crowned by a papillose knob; [exothecial cells with thin spots].||Polytrichastrum papillatum|
|3||Lamellae crenulate in profile||> 4|
|3||Lamellae entire in profile||> 5|
|4||Marginal cells of lamellae in section narrow, pyriform, thickened in the narrowed apex||Polytrichastrum appalachianum|
|4||Marginal cells of lamellae in section wider than those beneath, flat-topped or shallowly retuse.||Polytrichastrum pallidisetum|
|5||Marginal lamina entire or obscurely denticulate, inflexed; leaf apex cucullate, rarely bluntly mucronate.||Polytrichastrum sexangulare|
|5||Marginal lamina toothed, plane or erect, not inflexed; leaf apex ending in a short awn||> 6|
|6||Marginal cells of lamellae in section wider than those beneath, transversely elliptic, the free wall conspicuously thickened, often brownish.||Polytrichastrum ohioense|
|6||Marginal cells of lamellae ovate to elliptic, usually slightly taller than wide, not or evenly thickened||> 7|
|7||Marginal lamina 5-9(-20) cells wide, somewhat incurved when dry; median sheath cells rectangular (3-5:1).||Polytrichastrum longisetum|
|7||Marginal lamina 2-5 cells wide, ± erect; median sheath cells elongate (5-9:1)||Polytrichastrum formosum|