From the Greek ptychios (folded) and mnion (a moss), probably in reference to the rugose leaves.

Dioicous or phyllodioicous. Plants forming loose turfs. Stems simple to sparingly branched; paraphyllia scarce. Leaves squarrose, broadly ovate, ±plicate near the base, rugose distally; apex acuminate and twisted; margin serrate in the acumen, entire below; costa absent, or very short, narrow and weak. Laminal cells linear, incrassate, pitted; basal cells rectangular, slightly pitted. Gemmae absent.

Capsules horizontal, curved, cylindrical, furrowed; annulus differentiated; operculum very long-rostrate. Peristome: exostome teeth with very conspicuous transparent zones along median line on outer face, densely horizontally striate at the base, papillose at the apex; endostome pale yellow, slightly longer than the exostome, with a high basal membrane, processes hyaline, keeled, papillose; cilia present. Spores globose, smooth.

Ptychomnion is characterised by its squarrose, rugose leaves.

A genus of three predominantly Southern Hemisphere species (Australasia, South America, South Pacific islands and the Subantarctic islands); one in Australia.

Hypnum sect. Ptychomnion Hook.f. & Wilson, in J.D.Hooker, Bot. Antarct. Voy. 2(2): 110 (1854); Ptychomnion (Hook.f. & Wilson) Mitt., J. Linn. Soc., Bot. 12: 536 (1869).
Type: P. aciculare (Brid.) Mitt.

Excluded Name

Ptychomnion cygnisetum (Müll.Hal.) Kindb., Enum. Bryin. Exot. 31 (1888).
Syntype: Hermit Island, Tierra del Fuego, J.D.Hooker; Burnst Island, Darwin Sound, C.Spegazzini; Port Cook, C.Spegazzini; Beagle Channel, Tierra del Fuego, Spegazzini; Auckland Island, New Zealand, Krone.

Although this species was reported from Australia by Jaeger & Sauerbeck (Adumbratio flore muscorum totius orbis terrarum. Part 8, Ber. Thätigk. St. Gallischen Naturwiss. Ges. 1876–1878: 211–454, 1878) and later authors, no collections of this species could be located.

In addition to P. aciculare on the mainland, A second species, P. densifolium (Brid.) A.Jaeger, occurs on Macquarie Island. That moss is characterised by its sheathing and more densely plicate leaf bases.

Milne, J. & Klazenga, N. (2012). Australian Mosses Online 31. Ptychomniaceae. Australian Biological Resources Study, Canberra. Version 24 May 2012. http://www.anbg.gov.au/abrs/Mosses_online/31_Ptychomniaceae.html