Plants: small, green, yellow-green, often reddish. Stems: 0.4–1(–1.5) cm; rhizoids pale to bright violet, purple, or rarely red-purple. Leaves: loosely set, ovate-lanceolate, weakly concave, 0.4–1(–1.5) mm; base not decurrent; margins plane to weakly revolute basally, entire to serrulate distally, limbidium absent; apex acute; costa short-excurrent, awn slender; alar cells similar to adjacent juxtacostal cells; proximal laminal cells abruptly quadrate to short-rectangular, 2–4:1; medial and distal cells (30–)40–60 × 8–14 µm, 3–4:1. : Specialized asexual reproduction by rhizoidal tubers, on long rhizoids in soil, purple-red or rarely orange, irregularly spheric, 60–80(–100) µm, cells 25–30 µm, smooth. Sexual: condition dioicous. [Capsule nutant, 1–3 mm]. Phenology: Capsules mature Apr–Jul (spring–summer).
Damp soil, soil over rock, disturbed sites. low to moderate elevations (0-1000 m). B.C., N.S., Ont., Que., Ariz., Calif., Idaho, Mass., Mo., Nev., Utah, Wash., Wis., s South America (Argentina, Chile), Eurasia, Atlantic Islands (Tenerife), Pacific Islands (New Zealand).
Gemmabryum violaceum is distinguished by the combination of violet rhizoids and small, spheric, red to purple-red or orange rhizoidal tubers. Gemmabryum ruderale is similar but has larger tubers, and European material at least has strongly papillose rhizoids compared to relatively smooth rhizoids of G. violaceum.