Polytrichum strictum
Polytrichum jensenii
bog haircap moss, hummock haircap, narrow-leaf haircap, polytrichum moss, slender haircap
6–12(–20) cm, simple, densely matted with wooly whitish to light-brownish tomentum.
3–12 cm.
2–5(–6) mm, erect to closely appressed when dry, erect-spreading when moist;
sheath oblong-rectangular, brownish, ± abruptly contracted to the blade;
blade narrowly lanceolate, acuminate, flat, with sharply infolded margins;
marginal lamina 6–7 cells wide, 1-stratose, entire to finely crenulate above, membranous and transparent, abruptly infolded and enclosing the lamellae and overlapping towards the apex;
costa toothed abaxially towards the apex, short-excurrent as a short, reddish brown awn;
lamellae bluntly crenate in profile, 5–8 cells high, the marginal cells in section pyriform, thick-walled, ending in a thickened knob, end cells of lateral lamellae ovoid and scarcely thickened at the apex;
sheath cells 45–80 × 7–10 µm, elongate-rectangular (5–7:1), narrower toward the margin;
cells of the marginal lamina transversely elongate, shorter and obliquely oriented towards the margins, very thick-walled and colorless.
(4–)6–10 mm, ± distant, not crowded; closely appressed, straight or erect-spreading and weakly flexuose when dry, erect-spreading to widely spreading or weakly recurved when moist, caducous at the base of blade;
sheath short, scarcely broadened and rather weakly differentiated;
marginal lamina narrow, 2–3 cells wide, erect to somewhat involute towards the apex, entire to finely and obscurely serrulate from the middle upwards, the teeth rather weak and distant;
costa smooth abaxially, ending in a short, weakly toothed tip;
lamellae crenulate in profile, 8–12 cells high, with paired, projecting knobs along the margins, the marginal cells in section rather narrow, retuse, thick-walled, brownish, smooth;
sheath cells rather short rectangular, 60–90 × 15–22 µm;
cells of the marginal lamina ± isodiametric;
perichaetial leaves with sheathing bases usually hidden by upper stem leaves.
2–4 cm, yellowish to reddish brown.
1.5–4.5 cm, brownish.
dioicous;
perichaetial leaves somewhat longer than the stem leaves, ending in a slender awn.
2–3 mm, short-rectangular to almost cubic (1–1.5:1), brownish, sharply 4-angled and prismatic, suberect, becoming horizontal when ripe;
peristome 200–230 µm, divided to 0.8, the teeth 64, obtuse.
2.5–3.5 mm, sharply 4–5-angled, short rectangular to cubic.
dirty white to light brown, enclosing the capsule.
7–9(–15) µm.
Polytrichum strictum
Polytrichum jensenii
Polytrichum strictum is widespread in the boreal regions of the Holarctic, and is one of the commonest low arctic representatives of the family (D. G. Long 1985), with survivals southward in relict bogs, for example in northern Indiana, northern Illinois, and northwestern Iowa, also in alpine situations in the eastern mountains to the Carolinas and Georgia. In Nunavut, it is known from Baffin, Bathurst, and Devon islands. Its characteristic habitat is on hummocks in Sphagnum bogs, in deep masses tightly bound together by dirty-white, wooly tomentum, with short, stiffly erect leaves, and cubical capsules, a clear correlation between a distinctive morphology, distribution, and ecology.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Polytrichum jensenii is a widely distributed plant of the high Arctic, with a sporadic disjunct occurrence southward, where its distribution is poorly documented. In Nunavut, it is known from Melville Island. In arctic America it replaces P. commune north of the tree line (D. G. Long 1985, as P. commune var. diminutum), and is notable for its rather fragile texture, entire to weakly toothed leaf margins, and caducous leaf blades. The marginal cells of the lamellae are similar to those of P. commune. Forms of P. swartzii have entire or nearly entire, caducous leaves, but the marginal cells of the lamellae are rounded quadrate and thin-walled, absent the distinctive, thickened knobs of P. jensenii and P. commune. Genetic evidence may support the recognition of P. jensenii as a distinct species (G. S. Derda and R. Wyatt 1999).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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