Polytrichum juniperinum
Polytrichum jensenii
juniper haircap moss, juniper polytrichum moss
(1–)4–5(–10) cm, simple, brownish tomentose only near the base.
3–12 cm.
3–6(–8) mm, densely imbricate, ± erect and almost straight when dry, erect-spreading to widely spreading when moist;
sheath oblong-rectangular, yellowish, tapering to the blade;
blade slender, bluish green and nitid, rather flat, with sharply infolded margins;
marginal lamina 5–7 cells wide, 1-stratose, entire or minutely crenulate, membranous and transparent, enclosing the lamellae and overlapping towards the apex;
costa usually somewhat toothed distally, excurrent, forming a subulate, toothed awn, the awn reddish brown throughout or slightly decolorate at tip;
lamellae bluntly crenate in profile, 6–8 cells high, the marginal cells in cross-section ovate to pyriform, thick-walled, ending in a distinct knob, smooth or rarely faintly papillose, the marginal cells of lateral lamellae (enclosed by the overlapping margins) ovoid and less strongly thickened;
sheath cells 70–100 × 6–10 µm, narrowly rectangular (4–6:1), narrower toward the margin;
cells of the broad marginal lamina transversely elongate, very thick-walled.
(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.
(1–)3–5 cm, stout, yellowish to reddish brown.
1.5–4.5 cm, brownish.
dioicous;
perigonial rosettes yellowish to reddish green;
perichaetial leaves longer than the foliage leaves, long-sheathing, the blade almost obsolete, ending in a slender yellowish or hyaline awn.
2.5–5 mm, rectangular, longer than wide (1.5–2:1), reddish brown to dark brown, glaucous when fresh, suberect, becoming horizontal when mature, sharply 4-angled and prismatic;
peristome 200–240 µm, divided to 0.6–0.8, the teeth 64, keeled at back.
2.5–3.5 mm, sharply 4–5-angled, short rectangular to cubic.
whitish to light brown, covering the capsule.
6–10(–12) µm.
Polytrichum juniperinum
Polytrichum jensenii
Polytrichum juniperinum occurs on a variety of substrates, but primarily in dryer situations than P. commune or P. strictum. It often forms extensive pure stands of a distinctive pale bluish green color from the reflection of light off the thin, membranous margins of the leaves. The narrow leaf blades are widely spreading and have short, reddish awns. Polytrichum juniperinum is common and generally distributed throughout continental North America. In the high Arctic, however, the species is rare and many older reports of it actually pertain to 5. P. hyperboreum (D. G. Long 1985).
(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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