Monographs Details: Leucodon
Authority: Buck, William R. 1998. Pleurocarpous mosses of the West Indies. Mem. New York Bot. Gard. 82: 1-400.
Description:Genus Description - Plants slender to fairly robust, in mostly bright- to dark-green, often dense, sometimes extensive, epiphytic mats. Primary stems creeping, slender, inconspicuous, with reduced, scale-like leaves, turning ca. 90° and becoming the secondary stem, the creeping stem continuing by a bud from near the base of the secondary stem, secondary stems erect, simple to sparsely and irregularly branched, rarely pinnate, often curved when dry, not or scarcely complanate-foliate; in cross-section with small thick-walled cells surrounding larger thinner-walled cells, central strand present or absent; paraphyllia none; pseudoparaphyllia filamentous to foliose, rarely absent; axillary hairs with 1-2 short brown basal cells and 2-4 elongate hyaline distal cells. Secondary stem and branch leaves similar, densely placed, appressed or secund when dry, rapidly wide-spreading when moist, lanceolate to ovate, often ± oblong, mostly short-acuminate, concave, ± plicate, broadly and shortly decurrent; margins subentire to serrulate or crenulate above, entire below, plane usually throughout, rarely recurved below; costa none; cells oval to ± linear, mostly smooth, rarely prorulose, firm- to thick-walled, often porose, often becoming longer in the extreme apex, sometimes shorter toward the margins, longer toward the insertion; alar cells numerous in extensive areas, subquadrate to oblate, extending well up the margins to ca. 1/2 the leaf length. Asexual propagula sometimes of flagellate branches from leaf axils. Dioicous. Perichaetia conspicuous; leaves strongly differentiated, erect, convolute, usually oblong-lanceolate, acuminate; margins entire, plane; costa none; cells linear, smooth, porose. Setae usually elongate, rarely very short, smooth or rarely roughened, yellow-brown, twisted when dry; capsules exserted or rarely immersed to emergent, erect and symmetric, subglobose to cylindric, usually narrowed at the mouth; exothecial cells short-rectangular, usually firm-walled; annulus not differentiated; operculum usually obliquely rostrate, rarely conic; peristome double but endostome much reduced or even sometimes appearing absent, inserted below the mouth, exostome teeth pale, often with a prostome, on the front surface with a ± straight median line, sometimes smooth but often coarsely papillose, not or scarcely trabeculate at back; endostome only a low basal membrane. Spores spherical, papillose, often large, at times multicellular. Calyptrae cucullate, large, often covering entire capsule, naked, smooth.
Discussion:Leucodon Schwagr., Sp. Musc. Frond. Suppl. 1(2): 1. 1816; Neckera sect. Leucodon (Schwagr.) Müll. Hal., Syn. Musc. Frond. 2: 91. 1850.
Discussion. Leucodon is characterized in our flora by simple or scarcely branched secondary stems with ecostate leaves, relatively short laminal cells, and numerous alar cells. Although dioicous, the plants are often fertile and the shortly exserted capsules emerge from sheathing perichaetial leaves. The peristome is pale and the teeth are papillose. The calyptra is cucullate, naked, and covers the entire capsule.
The genus has recently been treated in Asia by Akiyama (1988), and much valuable morphological discussion is included there. However, Akiyama claims that Leucodon has a well-developed annulus, perhaps because of a difference in terminology. Although the cells near the mouth of the capsule are indeed differentiated from the other cells of the exothecium, I do not consider this an annulus. I use the term for a structure that is deciduous, even if tardily so, and no such structure is present in Leucodon.