Monographs Details: Thelia
Authority: Buck, William R. 1998. Pleurocarpous mosses of the West Indies. Mem. New York Bot. Gard. 82: 1-400.
Description:Genus Description - Plants medium-sized, in stiff, dull, green, sometimes glaucous, yellow-green to grayish, dense mats. Stems creeping or occasionally crowded and ± ascending, usually densely radiculose, especially in older parts, without primary and secondary stem differentiation, branches arising laterally from creeping stems, mostly regularly pinnate, less often irregularly branched, the branches ascending, mostly simple, short, terete to julaceous; in cross-section with small thick-walled cells surrounding larger firm-walled cells, central strand present; paraphyllia few to abundant, especially on stems, polymorphous, mostly foliose, ± short-ciliate, the cells smooth or papillose over lumina above; pseudoparaphyllia ? none (not found); axillary hairs with a single relatively short brown basal cell and 2 ± elongate hyaline distal cells. Stem and branch leaves similar or differentiated, stem leaves when differentiated somewhat larger and broader than branch leaves, ciliate; branch leaves imbricate dry or moist, more turgid when moist, deltoid-ovate, long-cuspidate, concave, ± decurrent; margins dentate to ciliate, the projections longer below, plane to erect; costa single, ending at or somewhat above midleaf; cells ± rounded-rhombic, stoutly unipapillose over the lumina, the papillae simple or forked, firm-walled, becoming longer, thicker-walled and smooth in the acumen and toward the insertion; alar cells subquadrate in basal angles, not reaching the costa, blending into other laminal cells above, upper ones papillose, lower ones smooth, enlarged toward the insertion. Asexual propagula none. Phyllodioicous. Perichaetial leaves pale, enlarged, erect and sheathing, oblong, gradually subulate; margins ciliate, plane; costa short or none; cells elongate, unipapillose in upper part of leaf. Setae elongate, smooth, yellow to orange, flexuose; capsules erect and symmetric, cylindric to ovoid-cylindric, gradually tapered to the mouth; exothecial cells short-rectangular, firm-walled; annulus none or poorly differentiated; operculum bluntly conic-subulate, slightly oblique; columella cylindric, ending shortly below midurn; peristome double, white, attached at or inserted slightly below the mouth, exostome teeth narrowly triangular, not shouldered, narrowly bordered, on the front surface smooth below, densely and finely papillose above, not trabeculate at back; endostome pale, papillose throughout, with a low basal membrane, segments short, irregular or rudimentary, cilia none. Spores spherical, ± smooth to finely roughened. Calyptrae cucullate, naked, smooth.
Discussion:Discussion. Thelia is a genus of three species confined to eastern North America. It is characterized by deltoid-ovate leaves with strikingly papillose, rhombic cells. The papillae are either simple or branched. The leaves, at least those of the stem, are more or less ciliate. The capsules are erect and symmetric with white peristomes. The genus differs from Anomodon by a dull, bluish cast, usually pinnate branching, broader leaves with weaker costae, and laminal lumina stoutly unipapillose. In the field Anomodon is immediately distinguished by its leaves widely spreading when moist (saliva is always available).
Thelia was monographed by Crum (1966), and at that time the genus was known only from eastern United States and Canada and northeastern Mexico. The extension of Thelia to Hispaniola (Buck, 1989b) represents another of that island’s continental affiliations (Steere, 1985).