From the Greek gonia (an angle or corner) and the Latin mitra (a turban or head-dress), in reference to the angled calyptra.

Paroicous, synoicous or autoicous. Plants small, brownish green to bright green, forming dense clusters. Stems reddish brown or pale, unbranched, rarely forked, to c. 2 mm tall, in cross-section with a central strand,  a medulla of parenchyma and weakly differentiated firmer-walled cortical layers. Stems beset below with reddish brown or cerise rhizoids that rarely bear ovoid tubers. Leaves appressed when dry, erect-spreading to spreading when moist, concave to somewhat keeled, ovate to obovate-spathulate, acute to acuminate-aristate; costa weakly to well developed, rarely absent, usually percurrent to excurrent; margins plane and entire. Upper laminal cells variable, often hexagonal to oblong, frequently some oblate; lower laminal cells more oblong or quadrate and often laxer, sometimes their walls undulate and weakly thickened at the corners; a row of yellowish brown cells frequently present across the leaf base; marginal cells not differentiated.

Male bud-like branch very short, beside the perichaetium. Calyptra broadly mitrate, with a short stout rostrum, with 8 radial pleats, 8-lobed at base, completely covering the immature capsule and often persisting after dehiscence. Setae yellow, 0.2–1.0 mm long, smooth, straight, not twisted. Capsules erect, symmetrical, ellipsoidal to globose (before dehiscence), globose to somewhat pyriform (after dehiscence), c. 1 mm long, operculate, gymnostomous, yellowish brown, strongly and irregularly wrinkled when dry, with a weakly differentiated neck to 1/5 the length of the capsule; mouth transverse, equal to or slightly less than the diameter of capsule; exothecial cells irregularly polygonal, c. 30–50 µm wide, with thin non-cuneate walls, c. 6 suboral rows oblate and firmer-walled; operculum plano-convex, not rostrate, falling with a portion of the columella attached, composed of irregularly arranged thin-walled cells; annulus weakly differentiated, composed of a single row of small firm-walled isodiametric to oblong cells, persistent; stomata numerous, weakly immersed. Spores ellipsoidal, yellowish brown to golden, minutely verrucate, the surface appearing reticulate; in polar view oval, occasionally almost isodiametric; in lateral view convex on the distal side, plane to slightly concave on the proximal side, with a long narrow aperture area or laesura, 60–110 µm in greater diam.

Goniomitrium Hook. & Wilson, London J. Bot. 5: 142 (1846). Type: not designated.

Rehmanniella Müll.Hal., Bot. Centralbl. 7: 347 (1881). Type: R. africana Müll.Hal. [= G. acuminatum subsp. africanum (Müll.Hal.) Fife].

Goniomitrium speluncae P. de la Varde was described from sterile material, and its affinities must remain in doubt. Of the four remaining taxa, G. seroi Casas de Puig from Spain is similar to G. acuminatum but the spores are smaller (37–50 µm). Goniomitrium africanum (Müll.Hal.) Broth., differs from Australian G. acuminatum in having shorter upper laminal cells with undulate walls in the upper part of the lamina, stouter and more excurrent costae, conspicuously redder rhizoids and spores 50–75 µm. Fife (1985) reduced G. africanum to a subspecies of G. acuminatum, although Magill (1987) retained it as a distinct species.

Catcheside, D.G. (1980), Mosses of South Australia 218–239.

Fife, A.J. (1982), Taxonomic and nomenclatural observations on the Funariaceae. I. Physcomitrium, Physcomitrella, and Goniomitrium in New Zealand, Lindbergia 8: 96–104.

Fife, A.J. (1985), A generic revision of the Funariaceae (Bryophyta: Musci). Part I, J. Hattori Bot. Lab. 58: 149–196.

Fife, A.J. & Seppelt, R.D. (2001), A revision of the family Funariaceae (Musci) in Australia, Hikobia 13: 473–490.

Magill, R.E. (1987), Flora of Southern Africa. Bryophyta. Part 1 Mosses. Fascicle 2. Gigaspermaceae–Bartramiaceae.

Scott, G.A.M. & Stone, I.G. (1976), The Mosses of Southern Australia. Academic Press, London.

Stone, I.G. (1981), Spore morphology and some other features of Goniomitrium Hook. & Wils. (Funariaceae), J. Bryol. 11: 491–500.

A.J.Fife & R.D.Seppelt (2012), Australian Mosses Online 67. Funariaceae. Australian Biological Resources Study, Canberra. Version 2 October 2012.