Plants 2-20 mm, perennial, sometimes gregarious but mostly in dense short turfs, green to yellow-green. Stems variable, simple, with few innovations, or often short and multi-branched by numerous innovations from axils of stem leaves or exterior perichaetial leaves, often becoming prostrate with age, innovations fragile and often detached. Stem leaves erect to erect-spreading, lanceolate, triangular or ovate-lanceolate, narrowly acuminate to subulate, 0.5-2 mm, becoming reduced proximally; costa percurrent to distinctly excurrent in hairpoint; laminal margins plane, smooth or finely serrulate distally; median laminal cells rhomboidal to prosenchymatous, 4-8:1, 45-90 × 9-15 µm, somewhat shorter distally and along margin, proximal cells short-rectangular to rectangular, 2-4:1, 25-60 × 12-16 µm, short-rectangular to quadrate in alar region in 2-6 rows extending 6-15 cells along proximal lamina margin; leaves of innovations similar to distal stem leaves except smaller, often sharply reduced proximally. Perichaetial leaves variable in shape, ovate, oblong, ovate-lanceolate to lanceolate, larger, 1-2 mm, short- to long-acuminate; costa percurrent to long-excurrent, often forming pellucid hairpoint; laminal margins smooth, plane or rarely weakly recurved; median laminal cells rhomboidal, linear-rhomboidal to prosenchymatous, 4-8:1, 45-140 × 9-15 µm, shorter distally and along margin, proximal cells hyaline, lax, rectangular to rhomboidal, 4-6:1, 50-90 × 12-18 µm. Specialized asexual reproduction absent. Sexual condition autoicous, antheridia terminating axillary leaf buds. Capsule lateral, or both lateral and terminal, 270-600 µm. Spores typically 16(4-60) per capsule, rounded-triangular to polyhedral, 110-320 µm, pale yellow, smooth to papillose.
1. Archidium ohioense Schimp. ex C. Müll. 中华无轴藓 zhong-hua wu-zhou xian Syn. Musc. Frond. 2: 517. 1851. Type. U.S.A., Sullivant, Musci Allegh. 213 (as Archidium phascoides Brid.). Archidium sinense Durieu in Debeaux, Bull. Soc. Bot. France 9: 161. 1862. Type. China: Shandong, Yan-tai near Teché-fou, Debeaus s.n., 1861. Plants gregarious to loosely tufted, 2–30 mm high, yellowish green to green, not glossy. Stems erect, simple or 2–3-branched by subapical or lateral innovations. Upper stem leaves erect-spreading to spreading, channelled, ovate-lanceolate or lanceolate to narrowly long-triangular, acuminate to subulate, 0.5–1.7 mm ´ 0.16–0.28 mm wide; margins entire to faintly serrulate above; costa percurrent to strongly excurrent; median cells rhomboidal to prosenchymatose, 45–90 mm ´ 9–14 mm, shorter toward the apex; basal cells short-rectangular to rectangular, those at alar regions quadrate in 2–6 rows. Autoicous; perichaetia and perigonia mostly lateral and sessile, occasionally terminal on short branches. Perichaetial leaves 1–2 mm long, ovate, oblong-ovate, ovate-lanceolate, or lanceolate, short- to long-acuminate; margins plane, entire to faintly serrulate above; costa percurrent to strongly excurrent; median cells rhomboidal to prosenchymatose, 45–140 mm ´ 9–14 mm, shorter above; basal cells loosely rhomboidal to rectangular. Rhizoids smooth, rhizoidal tubers present. Capsules lateral or occasionally terminal, about 0.4 mm broad. Spores 4–60, often 16, per capsule, 110–310 mm, irregularly angled, smooth to densely papillose.
Two growth forms of A. ohioense can be recognized in Southern Africa. In the short `form', branching is mostly by subperichaetial innovations; the stem leaves are rapidly reduced to ovate-lanceolate bracts below, and the perichaetial leaves are large, broadly ovate-lanceolate and have percurrent to excurrent costae. The tall, little branched, subflexuose `form' has lateral perichaetia. The narrowly long-triangular stem leaves are distant, widespreading and reduced only near the stem base. The perichaetial leaves in this `form' are smaller with a more or less percurrent costa. Although there is a complete gradient from the short `form' to the tall `form' in North America, this is not evident in Southern Africa. The tall, subflexuose `form' occurs in moist, shady habitats and is known in Southern Africa from a single specimen collected in the Ngoya Forest of Zululand. The short `form' is more common and occurs in drier, open habitats.
Plants forming loose turfs, yellow-green; terricolous. Stems erect or subflexuose, 2-15 mm high, simple or branching; in section with central strand, cortical cells large, thin- walled, outer 1-2 rows smaller. Leaves bract-like below, erect-spreading or wide-spreading above, ovate-lanceolate to ovate or occasionally narrowly lanceolate, short-acuminate to subulate, 0.9-1.5 mm long; base often clasping; margins plane, entire or serrulate above. Costa percurrent to excurrent as hair-point; in section cells undifferentiated. Laminal cells rhomboidal to fusiform, basal cells rectangular to quadrate. Perichaetia terminal or lateral. Leaves erect, ovate, oblong-ovate, ovate-lanceolate or lanceolate, acuminate, 0.7-1.8 mm long; margins plane to recurved; entire to serrulate above. Costa percurrent to excurrent as hair- point; in section round, cells undifferentiated, incrassate. Laminal cells rhomboidal to fusiform, frequently lax, 37-95 µm long, walls (1.7-)2.8(-4.4) µm wide, lumen (7-)12-15 µm wide; basal cells rhomboidal to rectangular, lax, hyaline below. Spores 8-60 per capsule, rounded triangular to polyhedral, 97-176 µm, smooth to granulose, yellow.
Plants forming loose turfs, yellow-green. Stems 2-15 mm long. Perichaetial leaves erect; ovate, oblong-ovate or lanceolate, 0.7-1.8 mm long; margins entire to serrulate above; costa percurrent to excurrent as hair-point. Laminal cells rhomboidal to fusiform, 37-95 jm long; basal cells rhomboidal to rectangular. Spores 8-60 per capsule, smooth to granulose, yellow.
This species is widely distributed and has been collected in North America, West Indies, India, Sri Lanka, Japan and Africa. In Southern Africa it is known from the southwestern and southern Cape, Zululand, Swaziland and the eastern and central Transvaal and South West Africa/Namibia.