Atrichum undulatum
Atrichum angustatum
common smoothcap, common smoothcap moss, undulate atrichum moss
atrichum moss, slender starburst moss
2–5 cm.
1–2 cm.
sparse below, more crowded above, 4–9 × 0.8–1.5 mm, lingulate to lanceolate, undulate, keeled distally, concave to flat proximally, with oblique rows of abaxial teeth on undulations, the apex acute;
costa percurrent, with teeth on abaxial surface in distal half;
lamellae 2–6, 2–4(–7) cells high;
median leaf cells 20–32 µm wide, irregularly angled to hexagonal, sometimes rounded, often transversely elongate, convex on both surfaces, smooth or with minute, verrucose or striate papillae on abaxial surface, walls firm, strongly collenchymatous with trigones.
4–8 × 0.4–0.8 mm, narrowly ligulate to oblong-lanceolate above, concave, strongly undulate, with prominent teeth in oblique rows on abaxial surface corresponding to the undulations, margins with mostly double teeth;
costa subpercurrent, toothed on the back above;
lamellae 6–9(–12), with wavy margins, 5–10(–15) cells high, widely spreading and covering much of the leaf surface;
median cells of lamina 8–17(–19) µm wide, ± isodiametric with firm walls, bulging-mammillose on adaxial surface, usually with prominent minute, rounded or striate papillae, especially on the abaxial surface.
1(–3) per perichaetium, 1–3 cm, reddish brown.
1–3 cm, erect, typically 1 per perichaetium.
polygamous, some shoots bisexual, others apparently male or female;
perigonial bracts broad, forming antheridial buds, often several buds per plant.
dioicous;
male plants about same size or smaller than females, the perigonial bracts broad, forming conspicuous antheridial buds, often with more than one bud in sequence per plant.
2–4(–8) × 0.5–1 mm, curved to distinctly arcuate, almost horizontal;
operculum 2–3 mm.
3–7 × 0.3–0.6 mm, narrowly cylindric, usually ± straight to somewhat curved, suberect or inclined.
(12–)16–28 µm.
11–16 µm.
Atrichum undulatum
Atrichum angustatum
No Atrichum species occurring in North America has been as widely misunderstood as A. undulatum. Evidently introduced from Europe, its weedy habitat and strongly arcuate, almost horizontal capsules are the surest means of recognition. Variety minus, a fixture of European manuals, is a stunted form that is highly variable and possibly a hybrid. Its occurrence in North America has not been demonstrated. As used by American authors (e.g., O. E. Jennings 1951), it probably refers to A. altecristatum.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Atrichum angustatum is a small, dioicous species, easily distinguished by its narrow, channeled leaves with numerous, tall, wavy lamellae, and small, ± isodiametric, bulging-mammillose, papillose leaf cells. A characteristic habitat for this species is mounds of subsoil thrown up by the roots of fallen trees. All Atrichum species develop cuticular papillae to some degree, but in no case are they as evident as in this species. Plants growing in more humid situations tend to be less strongly papillose. The distinction between A. angustatum, with smooth cells, and A. xanthopelma and A. macmillanii, with papillose cells, is without merit. The leaves of the type of A. angustatum (from South Carolina) are strongly papillose.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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