Monographs Details: Squamidium
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 to ± robust, in lustrous, mostly soft, pale-green to golden, often black-tinged colonies. Stems creeping or pendent, irregularly branched, the branches mostly short and simple; in cross-section with small thick-walled cells surrounding larger thinner-walled cells, central strand weak, of small thin-walled cells; paraphyllia absent; pseudoparaphyllia foliose; axillary hairs with 1-2 quadrate to short-rectangular brown basal cells and 2-5 long-rectangular hyaline to lightly colored distal cells. Stem and branch leaves often differentiated, especially in shape and length of apex, little altered when moist except that branch leaves then ± conspicuously ranked, erect to erect-spreading, mostly oblong-ovate, sometimes broadly so, abruptly acute to hairpointed, concave, ± clasping the stems, broadly long-decurrent; margins subentire to serrulate or (extralimitally) the stoloniferous stem leaves sometimes with large recurved teeth, plane or more typically incurved above; costa single, slender, often ending near base of acumen but sometimes weaker, irregularly short and double; cells linear, smooth, firm-walled, mostly porose; alar cells strongly differentiated in discrete, ± excavate groups, subquadrate and thick-walled or less often short-rectangular and thin-walled. Asexual propagula sometimes of flagellate branches arising from branch leaf axils. Dioicous. Perichaetia conspicuous, on branches; leaves differentiated, erect, convolute with flexuose-spreading apices, broadly oblong-lanceolate, ± gradually acuminate; margins subentire to serrulate, plane; costa single but weak, rarely absent; cells linear-flexuose, smooth, thick-walled, porose, becoming laxer toward the insertion; alar cells not differentiated. Setae short to very short from a hairy vaginula, smooth, yellow to orange; capsules immersed to short-exserted, erect, symmetric, cylindric to broadly cylindric; exothecial cells short-rectangular, firm-walled, becoming shorter toward the mouth; annulus differentiated, of thick-walled cells, tardily deciduous; operculum short-rostrate; exostome teeth scarcely or not shouldered, mostly not bordered, on the front surface ± papillose throughout, not or scarcely trabeculate at back; endostome with a medium-high basal membrane, segments slender, ± keeled, not or narrowly perforate, cilia rudimentary to absent. Spores spherical, lightly roughened. Calyptrae mitrate, lobed at base, sparsely to densely erect-hairy, smooth.
Discussion:Squamidium (Miill. Hal.) Broth, in Engl. & Prantl, Nat. Pflanzenfam. 1(3): 807. 1906; Meteorium sect. Squamidium Müll. Hal., Linnaea 42: 420. 1879.
Discussion. Squamidium is a genus of seven species, all of which occur in the Neotropics, with one of them, S. brasiliense (Hornsch.) Broth., disjunct to eastern and southern Africa. The genus is characterized by soft, mostly pendent plants that are often tinged with black. The stem leaves are often hairpointed, but branch leaves, with the exception of a very common species, are acute to acuminate. The costae are single and the laminal cells linear and smooth. The alar cells are strongly differentiated, often in excavate, colored groups. The plants are dioicous and rarely fertile, with mostly immersed capsules. (Two extralimital species have shortly exserted capsules.) Squamidium may be told from superficially similar Meteoriaceae by the combination of smooth laminal cells and strongly differentiated alar cells.
Squamidium was monographed by Allen and Crosby (1986b), and that publication can be consulted for more detailed accounts of the species treated here. In the West Indies we have four species of Squamidium, two of which, S. leucotrichum and S. nigricans, are common, and two that are rare, known from only a handful of collections.