Monographs Details: Thamnobryum
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 or more often robust, stipitate-frondose, in slightly lustrous to dull, dark- to yellow-green, often extensive colonies. Primary stems creeping, secondary stems arising from upturning primary stem, the creeping stem continuing by innovations near the base of the stipe, the secondary stems distinctly stipitate, erect to sometimes pendent, frondose, sparsely to densely, irregularly to pinnately branched, ± complanate-foliate; in cross-section with small thick-walled cells surrounding larger thinner-walled cells, central strand small but distinct, of small thin-walled cells; paraphyllia absent; pseudoparaphyllia foliose; axillary hairs with 1-2(-5) short brown basal cells and 1-5 elongate usually hyaline distal cells. Primary creeping stem leaves and those of the stipe similar, but those of stipe larger, usually spreading on primary stem, appressed with spreading apices on stipe, not complanate, ± triangular, decurrent or not; margins mostly subentire; costa single but often obscure, sometimes absent; cells mostly elongate, smooth, thick-walled, those of primary stem leaves often laxer; alar cells not or scarcely differentiated. Secondary stem (continuation of stipe above branching) leaves and branch leaves similar, those of branches sometimes smaller, ± complanate, mostly spreading, ovate, ovate-lanceolate, oblong-ovate or oblong-ligulate, obtuse and mucronate to short-acuminate, sometimes plicate, not or scarcely decurrent; margins serrate to serrulate at apex, subentire to serrulate below, plane or narrowly recurved; costa single, strong, ending ca. 4/5 the leaf length to subpercurrent, sometimes roughened at back; cells mostly long-hexagonal at midleaf, smooth or rarely prorulose, firm- to thick-walled, ± porose, becoming noticeably shorter at apex, rhomboidal to hexagonal, usually becoming longer toward the insertion; alar cells not or poorly differentiated. Asexual propagula rarely of microphyllous flagellate branches. Dioicous. Perichaetial leaves oblong-ovate to lanceolate, usually abruptly broad-acuminate; margins often toothed at extreme apex, subentire below, plane; costa single or absent; cells linear-rectangular, smooth, thick-walled, often becoming laxer toward the insertion. Setae elongate, smooth; capsules inclined or horizontal to pendent, cylindric; exothecial cells quadrate to rectangular, firm- to thick-walled, stomata present; annulus differentiated; operculum obliquely rostrate from a conic base; peristome double, attached at the mouth, exostome teeth on the front surface cross-striolate below, papillose above, strongly trabeculate at back; endostome with a high basal membrane, segments smooth or more often papillose, keeled, perforate to gaping, cilia in groups of 2-3, elongate, mostly appendiculate. Spores spherical, finely papillose to apparently smooth. Calyptrae cucullate, naked, smooth.
Discussion:Thamnobryum Nieuwl., Amer. Midi. Naturalist 5; 50. 1917; Thamnium Bruch & Schimp. in Bruch, Schimp. & W. Gtimbel, Bryol. Eur. 5(fasc. 49-51, Monogr. 1): 211. 1852, horn, illeg., non Vent., Tabl. Règn. Vég. 2: 35. 1799, nom. rej. [lichenized Ascomycetes, - Roccella A. DC. in Lam. & A. DC.], nec Klotzsch, Linnaea 12: 223. 1838 [Ericaceae, = Scyphogyne Decne. in Brogn. in Duperrey]; Hypnum sect. Thamnium (Bruch & Schimp.) Sull. in A. Gray, Manual, ed. 2, 669. 1856; Neckera sect. Thamnium (Bruch & Schimp.) Mitt., J. Linn. Soc., Bot. 4: 89. 1859; Porotrichum sect. Thamnium (Bruch & Schimp.) Mitt., J. Linn. Soc., Bot. 12: 459. 1869; Hypnum subgen. Thamnium (Bruch & Schimp.) Hobk., Syn. Brit. Mosses 145. 1873; Arbuscula H. A. Crum, Steere & L. E. Anderson, Bryologist 67: 163. 1964, nom. illeg.
Discussion. Thamnobryum is a genus of 20-30 species with its center of diversity in the Old World. The plants are typically robust and stipitate-fiondose, and they generally grow on wet rocks. Distinctive features of the genus are the strong single costa, leaves with short apical cells, and sporophytes with very long setae, inclined to pendent capsules, and a well-developed hypnoid peristome.