Monographs Details: Amblystegium
Authority: Buck, William R. 1998. Pleurocarpous mosses of the West Indies. Mem. New York Bot. Gard. 82: 1-400.
Description:Genus Description - Plants slender, in dull, stiff to soft, green, yellowish, or brownish mats. Stems creeping, irregularly or subpinnately branched; in cross-section without a hyalodermis, with small thick-walled cells surrounding larger thinner-walled cells, central strand present, of small thin-walled cells; paraphyllia absent; pseudoparaphyllia foliose, small; axillary hairs with a single short brown basal cell and a single elongate hyaline distal cell. Stem and branch leaves similar, stem leaves somewhat larger, erect to erect-spreading when dry, erect- to wide-spreading when moist, not falcate-secund, lanceolate to ovate, gradually to ± abruptly acuminate, ± concave; margins entire or serrulate, plane; costa single, ending at or near midleaf; cells rounded-rhombic to rounded-oblong-hexagonal, 3-8:1, often short, smooth, thin- to firm-walled, becoming longer and broader toward the insertion; alar cells poorly differentiated, subquadrate to oblate. Asexual propagula none. Autoicous. Perichaetia greatly enlarged, conspicuous; leaves erect from a ± sheathing base, lanceolate, acuminate, sometimes plicate; margins serrulate, plane; costa single or absent; cells long-hexagonal to long-rectangular, smooth, becoming shorter toward the insertion. Setae elongate, smooth, reddish, twisted when dry; capsules inclined, arcuate to almost straight, ± asymmetric, cylindric to oblong-cylindric, constricted below the mouth when dry; exothecial cells ± rectangular, firm-walled, not collenchymatous, stomata long-pored; annulus differentiated in 2-4 rows of thin-walled, deciduous cells; operculum conic, apiculate to short-rostrate, sometimes obliquely so; exostome teeth yellow-brown, shouldered, bordered, on the front surface cross-striolate below, coarsely papillose above, trabeculate at back; endostome with a low to high basal membrane, segments keeled, perforate, usually ca. as long as the teeth, cilia in groups of 1-3, or absent. Spores spherical, finely papillose. Calyptrae cucullate, naked, smooth.
Discussion:Amblystegium Schimp. in Bruch, Schimp. & W. Gümbel, Bryol. Eur. 6 (fase. 55-56, Monogr. 1): 45. 1853; Hypnum sect. Amblystegium (Schimp.) Sull. in A. Gray, Manual, ed. 2, 677. 1856; Stereodon sect. Amblystegium (Schimp.) Mitt., J. Linn. Soc., Bot. 8: 43. 1864; Hypnum subgen. Amblystegium (Schimp.) Hobk., Syn. Brit. Mosses 162. 1873.
Discussion. Amblystegium has small plants with short leaf cells. The single costa is variable in length and the alar cells are poorly developed. The plants typically grow in wet places, and often in exposed or disturbed ones.
Crum and Anderson (1981: 922-944) treated Amblystegium in a conservative, if not reactionary, manner, encompassing Leptodictyum and Hygroamblystegium. Although I sympathize with their frustration over the extreme variability encountered in the genus, even they admit to the naturalness of the segregate genera. Therefore. I have chosen to recognize the three genera, not only because of microscopic criteria, but also because of differences in aspect and habitat.
Amblystegium has been treated for North America on several occasions. The oldest and probably still the most useful treatment is Cheney’s (1897) monograph of the genus. Numerous type specimens were examined and very detailed descriptions were presented. Similar in concept are du Buysson’s (1883, 1886) earlier treatments of the European taxa of Amblystegium (s.l.). Grout’s (1931) solution to the variation in Amblystegium was to recognize numerous infraspecific taxa. Conard’s (1959) treatment of Amblystegium (s.l.) provided little new information but presented an interesting synopsis of the taxa and their character states.
Cheney (1897: 238) provided an apt introduction to Amblystegium: “After long study I am fully convinced that the genus will always prove a troublesome one to the systematist.”