In comparison with G. dichotomum and G. radiculosum, this species has longer and narrower capsules. Sterile specimens are sometimes difficult to distinguish from G. dichotomum. The lanceolate leaves with short-excurrent costae and the reddish tubers will help to identify specimens of G. subapiculatum.
Plants small to medium-sized, loosely caespitose to caespitose, green above, yellowish brown or reddish brown below; terricolous or humicolous. Stems 3-15 mm tall, simple or branching by subperichaetial innovations, tomentose below; rhizoids reddish or reddish brown, papillose, tubers (80-)200-300 µm, red or red-brown. Leaves larger above, erect and slightly twisted dry, erect-spreading wet; lanceolate, oblong-lanceolate or elliptical, (0.8-)1.0-2.0(-2.2) mm long; apex acuminate; margins plane to recurved below, denticulate above; border generally absent. Costa mucronate to short-excurrent, occasionally reddish below, awn 0.1-0.3 mm long; in section subround, lamina inserted ventrally, ventral surface cells present, dorsal stereid band in 1-3 rows, dorsal surface cells incrassate, hydroids forming large gap between guide cells and stereid band. Upper laminal cells rhomboidal, thin-walled or occasionally incrassate, frequently narrower and incrassate towards margin, 40-68 (-98) µm long, 10-18 µm wide; basal cells rectangular to quadrate, thin-walled or incrassate, occasionally pitted. Propagulae not seen. Dioicous. Perichaetia terminal, leaves lanceolate to narrowly triangular, margins recurved. Seta 12-28 mm long, yellowish to red; capsule pendulous, oblong-cylindrical or narrowly pyriform, yellowish brown, reddish brown to red, urn 1.0-2.2 mm long, neck wrinkled when dry, frequently curved, 0.8-1.2 mm long; exothecial cells irregular in shape, incrassate, smaller towards mouth, 1-3 rows at mouth transversely elongated; peristome double, exostome teeth narrowly oblong-acuminate, bordered, yellow, orange or red-brown below, hyaline above, minutely papillose, endostome segments tapered above, broadly perforated, cilia 2-3, nodose to appendiculate, basal membrane high, yellowish, minutely papillose; operculum conical, mammillate; calyptra cucullate; spores 11-14 µm, smooth to minutely granulose.