Monographs Details: Leiodontium
Authority: Buck, William R. 1987. Bryostephane Steereana: A Collection of Bryological Papers Presented to William Campbell Steere On The Occasion of His 80th Birthday. Mem. New York Bot. Gard. 45: 1-749.
Family:Hypnaceae
Scientific Name:Leiodontium
Discussion:Leiodontium was described by Brotherus (1929) for two Chinese species, L. gracile Broth. and L. robustum Broth. Subsequently, only one other species has been described (Dixon, 1937).

The genus is characterized by fairly slender, glossy plants which are subterete and slightly tumid. The leaves are broadly inserted, lanceolate-triangular to ovate-triangular and serrate except at the extreme base. The costa is short and double and the leaf cells are smooth and linear. The setae are slender and smooth, and the capsule is short and erect. The annulus is composed of a single row of deciduous cells even though described as absent. The exothecial cells are large, thin-walled and ± isodiametric. Although described as smooth and perforate, the exostome teeth are, in fact, neither. However, the front layer of each tooth is thin and hyaline, and since the back layer is more strongly pigmented and perforate above, Brotherus (1929) failed to see the ornamentation of the front surface. It is cross-striolate below, becoming papillose toward mid-tooth (initially with papillae in rows) and smooth above. The endostome is smooth and has a medium-high basal membrane (ca. 4 cells high), not or only slightly keeled, but perforate segments about as long as the teeth, and no cilia. The operculum is conic rostrate. Spores are finely papillose and about 12-15 µm in diameter. Among the two species described when the genus was proposed, only Leiodontium gracile is fertile and I here select it as the lectotype of Leiodontium. The third species, L. complanatum Dix., does not belong in the genus, or even the family and is dealt with below.

Ando (1975) suggested that Leiodontium may be synonymous with Stenotheciopsis Fleisch. (Figs. 8, 9). Although the two share a similar stature and both have leaves serrate almost throughout, Leiodontium is distinct in its ± triangular leaves (broadest at insertion), more slender acumina and less serrate margins. Most striking, the laminal cells of Stenotheciopsis serrula (Mitt.) Fleisch., the only species in the genus, are only about 5:1, whereas in Leiodontium they are 10-15:1.

two species of Leiodontium may be separated as follows:

1. Leaves ± lanceolate, 0.6-1.0 mm long. L. gracile (Figs. 1-7).

1. Leaves ± ovate, 1.1-1.7 m long. L. robustum (Figs. 10-15).

Leiodontium complanatum is placed in the following new genus.