Polytrichastrum alpinum
Polytrichastrum appalachianum
alpine haircap, alpine polytrichastrum moss
(1–)4–6(–14) cm, densely leafy above, often leafless and thread-like below, simple or sparingly to fasciculately branched.
2–6.5 cm high, simple, often felted with whitish rhizoids.
(4–)5–8(–19) mm, loosely to densely imbricate, erect-spreading and subtubulose when dry, erect-spreading to widely spreading when moist;
sheath ± nitid, elliptic to obovate, with tapering shoulders (in var. fragile contracted above the sheath and the blade caducous), broadly hyaline-margined;
blade linear-lanceolate, the apex narrowly acute to finely acuminate;
marginal lamina 2–5 cells wide, erect, coarsely serrate with multicellular teeth, distantly serrulate to subentire;
costa excurrent, ending in a short, brownish, toothed awn;
lamellae 5–8 cells high, entire in profile, the marginal cells with the free wall appearing greatly thickened, the marginal cells in section enlarged, yellowish to dark brown, ovate to narrowly ovate, the lateral walls strongly thickened, the lumen narrowly pentagonal and pointed at the apex, coarsely papillose;
median cells of sheath 40–60(–80) × 6–12 µm, elongate-rectangular, thin-walled;
cells of the marginal lamina 10–15 µm, subquadrate, sometimes transversely elongate;
perichaetial leaves scarcely longer than the stem leaves.
5–10 mm, erect-spreading when dry, widely spreading and somewhat recurved when moist;
sheath about 2 mm, hyaline-margined, the cells at the shoulders forming a differentiated hinge;
blade lanceolate, acuminate, sharply serrate nearly to the sheath;
costa short-excurrent, ending in a short, brownish or reddish brown point;
marginal lamina plane to erect, 2–8(–20) cells wide;
lamellae 18–50, crenulate in profile, 4–7 cells high, marginal cells in section narrow, pyriform, thickened at the narrowed apex, smooth;
sheath cells rectangular, 4–6:1;
cells of marginal lamina 9–13 µm, rounded to subquadrate.
(1–)3–5 cm, brownish.
3.5 cm.
dioicous;
perichaetial leaves not much differentiated.
various, (1.5–)3–5(–8) mm, terete, narrowly cylindric to oblong-cylindric and curved, ovate-cylindric, or ovoid to almost spherical, suberect to inclined to almost horizontal;
hypophysis tapering, rugose, with numerous conspicuous stomata in a broad basal band;
exothecial cells irregularly rectangular, not bulging or mammillose, thin spots absent, rather thick-walled;
peristome 600 µm (teeth 150–250 µm), divided to 0.6–0.75, the teeth 45–50, with some teeth irregularly developed and unequal, pale to somewhat darker in the median line.
4.5–5 mm, 4-angled;
hypophysis cylindric but not sharply delimited;
exothecial cells absent a central thin spot.
14–20 µm.
11–13 µm.
Polytrichastrum alpinum
Polytrichastrum appalachianum
Varieties 8 (4 in the flora).
Polytrichastrum alpinum is highly variable in habit and plant size, dentition of the leaves, and capsule shape. However, all forms of the species are easily recognized by the entire-margined, coarsely papillose lamellae and terete capsules with smooth, non-pitted exothecial cells. The marginal cells of the lamellae in section are distinctive in shape and wall thickening, elegantly described by A. J. E. Smith (2004) as “strawberry-shaped.” The wall thickenings extend down the lateral walls, so that in profile the free margin appears to be much thicker-walled and the lumen more restricted than is actually the case. The marginal cells of P. sexangulare are similar in shape and wall thickening, but smooth. The only North American taxa of Polytrichaceae likely to be confused with P. alpinum when sterile are Meiotrichum lyallii and Pogonatum urnigerum. In P. urnigerum the marginal cells of the lamellae are shorter and broader at the apex with a pentagonal lumen; in M. lyallii the marginal cells seen in profile are irregularly striate and pitted rather than papillose.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Polytrichastrum appalachianum is locally common on exposed mountain summits in the Blue Ridge and Great Smoky mountains, and was long misidentified as Polytrichum gracile. The marginal cells of the lamellae are pear-shaped in section and crenulate in profile, whereas in Polytrichum gracile and Polytrichastrum formosum the marginal cells are scarcely differentiated, and the lamellae in profile are entire or finely and distantly serrulate. This species was for a time confused with Polytrichum xanthopilum (Mitten) G. L. Smith, a Himalayan plant with similar lamellae, but a different capsule shape (see H. A. Crum and L. E. Anderson 1981). The capsule of Polytrichum xanthopilum has a broad annular constriction separating the hypophysis from the urn.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
1. Plants medium to robust; leaves sharply serrate; capsules short- to long-cylindric | → 2 |
1. Plants small (1-2 cm); leaves entire to finely and remotely serrate toward the tip; capsules ovoid to subglobose | → 3 |
2. Plants medium, (2-)4-6(-10) cm; leaves (4-)5-8 mm; capsule 3-5 × 0.8-1 mm, short-cylindric or slender and subarcuate. | var. alpinum |
2. Plants robust, to 14 cm; leaves 12-14(-19) mm; capsule 5-8 × 1.5-2.2 mm, often ± zygomorphic and widest below the middle. | var. sylvaticum |
3. Leaves not fragile, not constricted at junction of sheath and blade, the blade persistent | var. septentrionale |
3. Leaves fragile, constricted at the junction of sheath and blade, the blade caducous | var. fragile |
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