Dioicous or monoicous. Stems erect, rigid, simple or branched, with a polytrichoid (solid hydrome cylinder) or dawsonioid (hydroids and sclerenchyma) central strand. Rhizoids hyaline. Lower leaves small, often scale-like, appressed, remote; upper leaves larger, often crowded, with a broad pale unistratose sheathing base and a narrow lamina that is often bi- to multistratose almost to the margin. Lamina with isodiametric ±smooth abaxial cells; cuticle sometimes longitudinally striate; margin mostly entire to distinctly serrate, sometimes with specialised elongated marginal cells; sheath cells mostly rectangular to linear, narrower towards margin; costa single, prominent, percurrent to slightly excurrent, usually broad and ill-defined in lamina; lamellae on adaxial side of costa and lamina.

Perichaetium terminal; perichaetial leaves scarcely differentiated, usually with a longer sheathing base. Perigonium rosulate, generally producing an annual innovation from the centre, with uni- to multiseriate paraphyses among antheridia; perigonial leaves with a wide-sheathing base and a rudimentary lamina. Calyptra small or large, mitrate or cucullate, rarely glabrous or apically serrate, often densely hairy. Setae terminal or pseudolateral by subperichaetial innovation, elongate, mostly single, smooth. Capsules erect, becoming slightly inclined to horizontal, symmetrical or asymmetrical, terete and cylindrical or angled; neck short and weakly differentiated or hemispherical, sometimes abruptly constricted from the urn as a hypophysis; stomata lacking or only on basal part of capsule; annulus absent or a single row of cells; operculum acute or rostellate. Peristome single; teeth 16–64, short, lingulate or triangular, curved inwards, attached at or near the rounded tips to a discoid expansion of the columella apex (epiphragm; lacking in Dawsonia), with a low or high basal membrane; in Dawsonia elongated with a bristle-like upper part. Peristome teeth consisting of whole elongated cells following the tooth shape in several concurrent rows, mostly pale except for a coloured midline. Spores globose, isomorphic, echinate, granulose or smooth (in Dawsonia).

Chromosome numbers are based on x = 7, with most Australian representatives having n = 7 chromosomes. Polyploidy to n = 14 is known in one taxon in Australia; see H.P. Ramsay, J. Hattori Bot. Lab. 82: 213–226 (1997).

The Polytrichaceae comprise 19 genera and c. 150–200 species. The family is widely distributed throughout the world, and diversity is highest in Southeast Asia and South America. It is represented in Australia (except for Western Australia and the Northern Territory) by seven genera and 14 species; two species are endemic.

Polytrichaceae Schwägr., in C.L. von Willdenow, Sp. Pl. 5(2): 1 (1830). Type: Polytrichum Hedw.

The genus Dawsonia was formerly segregated in the monotypic Dawsoniaceae, but it was transferred to the Polytrichaceae by Smith (1971). Some authors (Zanten, 1973; Beever et al., 1992; Streimann & Klazenga, 2002) agree with this move, while others (Scott & Stone, 1976; Catcheside, 1980; Walther, 1983; Jarman & Fuhrer, 1995; Ramsay, 1997) maintain the Dawsoniaceae as a separate family.

The key published here is based on gametophytic characters to facilitate the identification of all specimens: sporophyte attributes, although they are characteristic for genera, are ignored in this context. Consequently, a key is provided only for species because gametophyte characters are usually not diagnostic for individual genera.

Atrichum can be distinguished from other genera by lacking or having only sparse lamellae on the adaxial side of the narrow costa and by its narrow, slightly curved capsules with long, membranous calyptrae; Notholigotrichum by the triangular shape of the peristome teeth; Pogonatum by the deep reddish brown pigmentation of the peristome; Polytrichastrum by the cylindrical, terete to faintly plicate capsules with stomata on the basal hypophysis; Polytrichum by its leaves having a sheathing base and a narrow, lanceolate limb and box-like capsules with four distinct angles; Polytrichadelphus by the calyptra which is glabrous except for a few terminal erect bristles, the long-beaked operculum, and the asymmetrical, concave-convex capsule that is almost crescent-shaped in transverse section; and Dawsonia by its concave-convex capsules and bristle-like peristome.

Beever, J., Allison, K.W. & Child, J. (1992). The Mosses of New Zealand, 2nd edn: 21–22. (University of Otago Press: Dunedin).

Catcheside, D.G. (1980). Mosses of South Australia. pp. 47, 65. (Govt. Printer: Adelaide).

Hyvönen, J., Hedderson, T.A., Smith Merrill, G.L., Gibbings, J.G. Koskinen, S. (1998). On phylogeny of the Polytrichales. Bryologist 101: 489–504.

Jarman, S.J. & Fuhrer, B.A. (1995). Mosses and Liverworts of Rainforest in Tasmania and South-eastern Australia. pp. 31, 52, 119. (CSIRO Australia: Melbourne).

Ramsay, H.P. (1997). Cytotaxonomic studies on some Polytrichales from Australia, New Zealand, Papua New Guinea and Vanuatu. J. Hattori Bot. Lab. 82: 213–226.

Scott, G.A.M. & Stone, I.G. (1976). The Mosses of Southern Australia. pp. 79–80. (Academic Press: London).

Smith, G.L. (1971). A conspectus of the genera of Polytrichaceae. Mem. New York Bot. Gard. 21: 1–83.

Walther, K. (1983). A.Engler’s Syllabus der Pflanzenfamilien, V, 2, Bryophytina, Laubmoose. p. 27. (Borntraeger: Berlin).

Zanten, B.O. van  (1973). A taxonomic revision of the genus Dawsonia R.Brown. Lindbergia 2: 1–48.

Hyvönen, J. (2012), Australian Mosses Online 48. Polytrichaceae. Australian Biological Resources Study, Canberra. Version 20 June 2012. 
http://www.anbg.gov.au/abrs/Mosses_online/48_Polytrichaceae.html

First published as:  Hyvönen, J. (2006), Polytrichaceae, in McCarthy, P.M. (ed.) Flora of Australia 51: 124–143. (Australian Biological Resources Study, Canberra & CSIRO Publishing, Melbourne).