Thysanomitrium uncinatum W. H. Harvey
Plants brown proximally, yellowish green or yellowish brown to dark green distally, glossy, in loose to dense tufts. Stems 2--8(--14) cm, radiculose proximally with reddish brown rhizoids. Leaves falcate-secund, especially at stem apices, sometimes erect and flexuose, spreading at ca. 30º when wet, 5--10 mm, occasionally deciduous, somewhat abruptly narrowed from an ovate to oblong base into a setaceous subula, subtubulose proximally, channelled distally, margins entire proximally, serrate to serrulate near apex, apex acute; costa distinct, occupying ca. 1/5--1/3 of leaf base; cells thick-walled and pitted only in leaf base, distal cells linear, 24--56 5--9 μm, basal cells broadly rectangular, hyaline, ca. 16 μm wide, alar cells not forming auricles, thin-walled, hyaline. Seta 8--11 mm, erect-sinuose to cygneous. Capsule 1.0--1.8 mm; operculum straight, ca. 1 mm. Spores 16--17 μm.
Dry or damp, acidic cliffs, primarily cliff ledges, sometimes on overturned tree roots and rotten logs in forests; 0--915 m; B.C.; Europe; Asia.
Sporophytes are not known or reported for North American plants. H. C. Gangulee (1971) reported them for eastern India where the plants fruited in October with capsules containing spores 16--17 µm. Dicranodontium uncinatum, the largest of the North American species of Dicranodontium, has stems usually 2--8 cm, sometimes up to 14 cm. It is easily recognized by its hook-shaped leaves. Dicranodontium uncinatum is often confused with D. denudatum, which has shorter leaves, mostly less than 8 mm, and are auriculate, with an indistinct costa and alar cells that are narrowly rectangular and usually reddish. In D. uncinatum the cells distal to the alar region and adjacent to the costa are broadly rectangular and hyaline.