Monographs Details: Rigodium
Authority: Buck, William R. 1998. Pleurocarpous mosses of the West Indies. Mem. New York Bot. Gard. 82: 1-400.
Description:Genus Description - Plants small to robust, in wiry, green to golden mats. Stems erect or sprawling, irregularly to regularly 1-3-pinnate above a differentiated stipe, each level of branching markedly smaller in stature than the previous ones; in cross-section with small thick-walled cells surrounding larger thin-walled cells, central strand of very small thin-walled cells; paraphyllia none; pseudoparaphyllia foliose; axillary hairs with 1-2 short brown basal cells and 1-2 elongate distal cells. Stem and branch leaves differentiated, stem leaves mostly wide-spreading, often ovate, usually abruptly acuminate, concave; margins serrate to serrulate, usually throughout, plane; costa single, ending in the acumen, often absent in stipe leaves; upper cells mostly rounded-hexagonal to short-rectangular, smooth, thick-walled, porose or not; alar cells often ± excavate but scarcely differentiated in size or shape from the cells above them. Branch leaves smaller than stem leaves, erect to erect-spreading, lanceolate to lanceolate-ovate, gradually to abruptly acuminate, often decurrent; margins serrulate to serrate, usually throughout, plane; costa single, ending in the acumen; upper cells rounded-isodiametric to oval to short-rectangular, smooth, thick-walled, not porose; alar cells not differentiated. Asexual propagula none. Dioicous. Perichaetia conspicuous; leaves erect to spreading, oblong-lanceolate, gradually long-acuminate; margins serrulate above, entire below, plane; costa single or none; cells short-rectangular to linear throughout, usually broader below. Setae elongate, smooth, reddish, curved above; capsules suberect to horizontal to nodding, symmetric to somewhat asymmetric, short-cylindric; exothecial cells thick-walled, not collenchymatous, stomata immersed, long-pored; annulus differentiated in 2-3 rows; operculum conic, short-rostrate; peristome double, attached at the mouth, exostome teeth shouldered, scarcely bordered, on the front surface cross-striolate below, papillose above, trabeculate at back; endostome with a high basal membrane, segments keeled, perforate to gaping, cilia in groups of 1-2, nodulose. Spores spherical, finely papillose. Calyptrae cucullate, naked, smooth or finely roughened above.
Discussion:Rigodium Kunze ex Schwagr., Linnaea 18: 559. 1844 ; Hypnum sect. Rigodium subsect. Rigodium (Schwägr.) Müll. Hal., Syn. Musc. Frond. 2: 444. 1851.
Discussion. Rigodium is a genus of five species distributed primarily in southernmost South America but ranging northward in the mountains to Mexico, and with an occurrence in Africa. It was monographed by Zomlefer (1993), whose work should be consulted for a more comprehensive view of the genus. The genus is most likely to be confused only with Thuidium, because of the superficial resemblance of branching pattern, but the lack of paraphyllia, the smooth laminal cells, and the stipitate habit readily separate it. Within our flora we have but a single species, described from Hispaniola.