A moss with leaflike phyllids. Similar in general appearance to haircap moss (Polytrichum), but smaller. A magnified view of the "leaves" shows an undulating toothed margin, giving the moss both its common and specific name.
Moist, well lit to partially shaded areas.
The genus name Atrichum refers to the lack of hairs (trichomes) on the calyptra (the lid of the sporangium). Genus Polytrichum has multiple hairs on the calyptra.