Plants small, in open to dense turfs, sometimes as scattered individuals, light green to pink-green, often brown proximally. Stems 0.5–2(–3) cm, evenly foliate, unbranched to freely branched by subfloral innovations; rhizoids few to many, macronemata absent. Leaves flexuose to weakly secund or sometimes imbricate when dry, erect to erect-spreading when moist, elliptic, ovate, oblong, or sometimes broadly lanceolate, somewhat concave, 0.5–2 mm; base not decurrent; margins plane or narrowly revolute proximally, entire or rarely weakly serrulate distally, 1-stratose, limbidium absent; apex rounded-obtuse to broadly acute or sometimes acuminate; costa subpercurrent to percurrent or rarely excurrent, hair-point present when excurrent, guide cells usually absent; alar cells irregularly short- to long-rectangular, not distinctly differentiated; laminal areolation homogeneous; proximal laminal cells rhomboidal to elongate-rhomboidal, 4–6:1; medial and distal cells rhomboidal to elongate-rhomboidal, 4–6:1, walls thin, not pitted. Specialized asexual reproduction absent. Sexual condition dioicous; perigonia and perichaetia usually appearing lateral due to rapid innovation growth, leaves same size as or somewhat smaller than vegetative leaves. Seta single, curved to flexuose. Capsule erect, horizontal, or nutant, subglobose to broadly pyriform, 1.2–2.5 mm; hypophysis not enlarged or inflated; operculum flat to convex, apiculate or umbonate; peristome single, typically exostomial but sometimes of unknown origin, or absent; exostome hyaline, teeth slender, irregularly linear-lanceolate. Spores not shed in tetrads, 10–20(–24) µm, smooth or finely papillose, pale.
North America, South America, Eurasia, Africa, Pacific Islands.
Species ca. 20 (2 in the flora).
Previous over-reliance on peristome characters has confused the taxonomy of Haplodontium and Mielichhoferia. The gametophytes of the two genera are very unlike, with Haplodontium species similar to those of Plagiobryoides and Plagiobryum. Recent genetic research has clearly shown that Mielichhoferia is related to Pohlia, while the species centered on H. macrocarpum are closer to Bryum and relatives. As our two species are very similar gametophytically to the type of Haplodontium, H. megalocarpum Arnott, they are here placed in Haplodontium. Peristome reduction is common and complex in this genus, from double to single to absent. The stems of Haplodontium are often densely tomentose proximally; the adaxial supracostal cells are elongate and similar to the adjacent laminal cells; the capsules are sometimes curved or irregularly shaped and often somewhat obscured by elongate innovations; and the exostome teeth are sometimes perforate.
|1||Peristome single; operculum flat to weakly convex, weakly apiculate; leaf margins narrowly revolute proximally; distal laminal cells at apex elongate; leaves flexuose to weakly secund when dry.||Haplodontium macrocarpum|
|1||Peristome absent; operculum convex, umbonate; leaf margins plane; distal laminal cells at apex short-rectangular to subquadrate; leaves imbricate when dry.||Haplodontium tehamense|