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
two species of Leiodontium may be separated
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.