Leucodon, a genus of 39 species (Crosby et al. 2000), is absent from Australasia but otherwise found throughout the world. The genus is predominantly corticolous, but it also occurs on rocks, and a few Leucodon species grow mostly on calcareous rocks. There are 20 species of Leucodon in east-ern Asia, and this area appears to be its center of diversity. In terms of morphological variation, Leu-codon in eastern Asia is especially noteworthy, e.g., Central American species of Leucodon lack a stem central strand and properistomial development, but some East Asian species of Leucodon have a stem central strand and extensively developed (sometimes chambered) properistomes.

Plants of Leucodon have four more or less distinct parts: stolons appressed to the substrate, sim-ple or irregularly branched secondary stems at more or less right angles to the stolons, flagellate branchlets, and pendent shoots. The genus has absolutely ecostate leaves and smooth, firm-walled leaf cells. The leaves typically have elongate cells in the basal median region and numerous quadrate to oblate alar cells. Leucodon is a dioicous genus with smooth, cucullate calyptrae and sheathing perichaetial leaves. The peristome in Leucodon consists of whitish yellow, narrowly triangular, and variously papillose exostome teeth and an endostome reduced to a short basal membrane.

The annulus in L. brachypus consists of several rows of small, thick-walled cells. Dehiscence oc-curs along an irregular line of weakness, and the annular cells are persistent, remaining attached to both the operculum and the capsule mouth. Akiyama (1988) characterized the annulus in Leucodon as “clearly differentiated.” Buck (1998), however, considered it absent because it was not a decidu-ous structure. I agree with Akiyama that an annulus is a structure that facilitates the separation of the operculum from the capsule along a distinct line.

The eastern Asian species of Leucodon were revised by Akiyama (1988). This treatment gives a detailed morphological analysis of the genus and divides the genus into three subgenera (Leucodon, Leucodontella (Nog.) Nog., and Cryptotheca Akiyama). Subgenus Leucodon is further divided into two sections (Leucodon and Macrosporiella (Dixon & Thér.) Akiyama).

The name Leucodon combines the Greek leucon (white) with odontos (tooth) and refers to the whitish yellow peristome found in the genus.