Atrichum undulatum
common smoothcap, common smoothcap moss, undulate atrichum moss
2–5 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.
1(–3) per perichaetium, 1–3 cm, reddish brown.
polygamous, some shoots bisexual, others apparently male or female;
perigonial bracts broad, forming antheridial buds, often several buds per plant.
2–4(–8) × 0.5–1 mm, curved to distinctly arcuate, almost horizontal;
operculum 2–3 mm.
(12–)16–28 µm.
Atrichum undulatum
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.)
BC
PNW Herbaria
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USDA Plants Database
