Autoicous, paroicous or synoicous. Plants annual or perennial, gregarious or scattered, terrestrial, 3–30 mm tall, yellowish or green, rarely pinkish. Stems erect or prostrate, frequently branched by sterile and fertile innovations, usually with a central strand, 2 layers of large thin-walled inner cortical cells and an outer cortex of 1 or 2 layers of similar or distinctly smaller cells. Rhizoids smooth, pale to deep brown, sometimes with propagules. Leaves erect to spreading, often clasping at the base, narrowly oblong, linear, lanceolate or ovate; apex obtuse, acute to acuminate or subulate; margin plane, incurved or recurved, entire to serrulate; laminal cells smooth, variously shaped (often in the same leaf); costa subpercurrent to excurrent, rarely absent or failing in mid-leaf; cells usually ±uniform in cross-section.

Gametoecia axillary or terminal. Perichaetial leaves mostly larger than stem leaves, sheathing; basal part often pale. Calyptra minute. Sporogone immersed. Setae absent. Capsules globose, cleistocarpous, gymnostomous; columella absent; exothecial cells large, irregularly hexagonal, yellowish to blackish; stomata absent. Spores few per capsule, large, polyhedral, 50–300 µm long; intine thick; exine smooth or papillose.

The family is characterised by the unique sporogone and large, distinctive spores, a delicate calyptra consisting mostly of archegonial neck, with remnants often attached to the vaginula, a bulbous foot embedded in a cup-shaped vaginula, a sessile capsule lacking an apiculus, with a single-layered wall at maturity and separated from the spore sac by a bell-shaped airspace.

Opinions regarding some features of sporogone morphogenesis vary and have been discussed by Snider (1975a, b) and Stone (1973, 1987). In contrast, the vegetative plant throughout the family is extremely variable and can resemble, for example, Bryum, Campylopus, Eccremidium, Ditrichum, Splachnobryum or Ephemerum. When lacking sporogones, species of Archidium are usually recognisable by a costa that lacks stereids, and readily deciduous innovations and perichaetia that join the stem by a single, short, haustorial cell.

A monogeneric family of approximately 30 species, widely distributed in tropical and temperate regions, but mostly native to Australia (16 species and three other distinct, but undescribed taxa) and Africa (14 species). Six of the named Australian taxa are endemic.

Archidiaceae Schimp., Coroll. Bryol. Eur. 5 (1856). Type: Archidium Brid.

Regeneration commonly occurs by new shoots from buried, moribund stems and rhizoidal tubers which are not uncommon in several species. Several species are efficient soil binders, having seasonal increments by repeated fertile and sterile innovations and copious rhizoids that become infiltrated and compacted with soil.

The family was revised by Snider (1975b) who divided it into two subgenera. Subgenus Archidium, the only one occurring in Australia, is further subdivided into four sections, three of which, Nanarchidium Snider, Protobium Müll.Hal. and Phascoidea G.Roth, occur in Australia.

Arts, T. & Magill, R.E. (1994), Rhizoidal tubers in Archidium indicum and A. yunnanense sp. nov., a new moss from China, J. Bryol. 18: 63–67.

Brotherus, V.F. (1924), Nat. Pflanzenfam., 2nd edn, 10: 155–156.

Magill, R.E. (1981), Archidiaceae, Fl. Southern Africa: Bryophyta 1(1): 71–81.

Snider, J.A. (1975a), Sporophyte development in the genus Archidium (Musci), J. Hattori Bot. Lab. 39: 85–104.

Snider, J.A. (1975b), A revision of the genus Archidium (Musci), J. Hattori Bot. Lab. 39: 105–201.

Spence, J.R. (2007), Archidiaceae Schimper, Fl. North America 27: 314–319. http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=102471

Stone, I.G. (1973), Two new species of Archidium from Victoria, Australia, Muelleria 2: 191–213.

Stone, I.G. (1987), The development of the Archidium capsule: clarification of a misconception, J. Bryol. 14: 745–751.

Stone, I.G. (1997), Archidium clarksonianum, a new moss species from Australia, J. Hattori Bot. Lab. 82: 271–279.

I.G.Stone (2012) Australian Mosses Online. 40. Archidiaceae. Australian Biological Resources Study, Canberra. Version 9 June 2012. http://www.anbg.gov.au/abrs/Mosses_online/Archidiaceae.pdf

First published as: I.G.Stone (2006), Archidiaceae, Flora of Australia Volume 51: 146–158. Australian Biological Resources Study, Canberra & CSIRO Publishing, Melbourne.