Monographs Details: Hygroamblystegium
Authority: Buck, William R. 1998. Pleurocarpous mosses of the West Indies. Mem. New York Bot. Gard. 82: 1-400.
Description:Genus Description - Plants slender to robust, in dull, ± stiff, yellow- to dark-green or blackish mats. Stems creeping, irregularly and often freely branched; in cross-section without a hyalodermis, with small thick-walled cells surrounding larger thinner-walled cells, central strand present or absent; paraphyllia absent; pseudoparaphyllia foliose, small; axillary hairs with a single short brown basal cell and 1-2 elongate hyaline distal cells. Stem and branch leaves often differentiated, erect dry or moist, not falcate-secund, oblong-lanceolate to oblong-ovate, gradually acuminate to a mostly broad, acute to obtuse apex, sometimes concave; margins usually entire, plane; costa single, broad, subpercurrent to excurrent, often filling the acumen; cells rhombic to oblong-hexagonal, mostly angular, 2-6:1, often short, smooth, firm-walled, becoming short-rectangular, broader, and often colored toward the insertion; alar cells not or poorly differentiated. Asexual propagula none. Autoicous. Perichaetia greatly enlarged, conspicuous; leaves erect, lanceolate, acuminate; margins often entire, plane; costa single, mostly percurrent to excurrent; cells long-hexagonal to linear, smooth, becoming shorter toward the insertion. Setae elongate, smooth, dark-red; capsules inclined, arcuate, asymmetric, cylindric to oblong-cylindric, ± constricted below the mouth when dry; exothecial cells short-rectangular, firm-walled, not collenchymatous, stomata long-pored; annulus of 2-4 rows of thin-walled, deciduous cells; operculum acute to apiculate to rostrate; exostome teeth yellow-brown, shouldered, bordered, on the front surface cross-striolate below, coarsely papillose above, trabeculate at back; endostome with a high basal membrane, segments keeled, not or narrowly perforate, rarely gaping, cilia in groups of 1-3, nodulose to appendiculate. Spores spherical, finely papillose. Calyptrae cucullate, naked, smooth, often small and falling early.
Discussion:Hygroamblystegium Loeske, Moosfl. Harz. 294. 1903, nom. cons.
Drepanophyllaria Müll. Hal., Hedwigia 38: 150. 1899, hom. illeg., non Müll. Hal., Nuovo Giorn. Bot. Ital. II, 3: 114, 115. 1896, nom. inval. [= Cratoneuron (Sull.) Spruce].
Discussion. Hygroamblystegium is characterized by mostly dark-green plants in mostly wet, even submerged habitats. The costa is generally stout and usually fills the leaf acumen. The leaf cells are firm-walled and relatively short, and the alar cells are not or scarcely differentiated.
Kanda (1975) suggested that the genus is characterized by shouldered stem leaves. However, his illustrations are unconvincing. I choose to recognize the genus on more traditional grounds, as described by Monkemeyer (1911). It is admittedly a segregate of Amblystegium, but the broader and longer costa, as well as a different areolation, seems to circumscribe a natural group of species.