Roellia roellii (Broth.) Andr. in Crum
Bryologist 70: 107. 1967. -- Mnium roellii Broth. in Roell, Bot. Centralbl 44: 420. 1890.
Bryum lucidum Britt., Bull. Torrey Bot. Club 18: 53. 1891. -- Mnium lucidum (Britt.) Broth., Hedwigia 32: 293. 1893.
Bryum sandbergii Holz., Contr. U. S. Nat. Herb. 3: 271. 1895.
Bryum simplex Kindb. in Mac., Cat. Can. Pl. 6: 135. 1892. -- Mnium simplex (Kindb.) Kindb., Rev. Bryol. 23: 22. 1896. -- Roellia simplex (Kindb. ex Mac. & Kindb.) Kindb., Sp. Eur. & North Amer. Bryin. 2: 346. 1897.
Plants erect in somewhat glossy green to brownish green turfs with yellow brown stems, to 2.5 cm high. Lower leaves scale-like, significantly reduced relative to the comose upper ones. Larger leaves spreading when moist, little changed dry, concave, to 6 mm long, oblong ovate to obovate, 2–3: 1. Median laminal cells regularly elongate-hexagonal, thin walled without corner thickenings, to 40 µm wide, about 4: 1, smooth. Basal cells not reddened, somewhat longer and more rectangular than median cells. Limbidium unistratose, comprised of only 1–3 rows of linear, pale to concolorous, elongate but thin-walled cells, abruptly differentiated from the adjacent laminal cells. Margins decurrent nearly to base of next lower leaf with that decurrency only 2–3 cells wide at juncture with main leaf, recurved from near the base. Margins recurved from base to near the middle, entire below but serrate distally, not geminate. Costa reddened near its base, filling less than 1/10 of leaf base, ending within a few cells of the rather blunt and somewhat reflexed mucro. Costa cross section with a median group of stereids surrounded on each side by 2–3 layers of large and thin-walled cells. Axillary hairs 8–10 cells long, to 150 µm, with two strongly pigmented basal brown cells giving way above to a series of nearly isodiametric cells and with only one or two terminal elongate cells. Rhizoids densely placed in the axils of the scale-like leaves at the base of plant, papillose, red-brown to almost red, to 15 µm in diameter at base, sparingly branched from a monopodial main axis. Stem cross-section rounded pentagonal with a prominent central strand, with leptodermous and hyaline inner corticals and with 1 layer of pachydermous, red brown, markedly smaller outer cortical cells.
Dioicous with male plants similar to the females. Perichaetia terminal with bracts markedly narrower and shorter than adjacent vegetative leaves. Seta yellow to reddish, smooth, erect, to 4 cm long. Urn yellow-brown to rather dark brown, to 6 mm long, 3–4: 1, cylindric, symmetrical. Operculum conic to apiculate, much shorter than the urn. Annulus well-defined, of several rows of thin-walled, isodiametric cells. Exothecial cells at capsule mouth thick walled, to 50 µm broad, mostly transversely elongated, strongly differentiated in up to 6 rows. Exothecial cells at middle of urn irregularly rectangular, 5–6: 1, to 25 µm broad, rather thick walled, in somewhat vertical rows. Stomata restricted to neck of capsule, phaneroporous, formed of two guard cells. Exostome teeth 16, pale to rather light yellow, to 800 µm long, finely and densely papillose striate below but papillose above. Endostome segments about as long as the peristome teeth, with basal membrane comprising about 1/2 of their length, lightly papillose, keeled with perforations short oblong to circular. Cilia 2–3, nodose. Calyptra cucullate, covering only the distal portion of the capsule. Spores light green, to 15 µm, smooth to finely papillose.