Orthodicranum rhabdocarpum (Sullivant) Holzinger
Plants in dense tufts, green to yellowish green or brownish, ± glossy. Stems 2--8 cm, tomentose with reddish brown rhizoids. Leaves straight or nearly so, spreading, little changed when dry, smooth, 3--5.5 ´ 0.6--1.2 mm, concave or tubulose below, tubulose to slightly keeled above; ovate-lanceolate, apex obtusely acute; margins serrate near apex; laminae 1-stratose; costa subpercurrent to percurrent, 1/10--1/8 the width of the leaves at base, smooth or weakly toothed on abaxial surface near apex, with a row of guide cells, two weak stereid bands, at least in basal part of leaf, adaxial and abaxial epidermal layers of cells not differentiated; cell walls between lamina cells not bulging; leaf cells smooth; alar cells 1- or 2-stratose in part, differentiated, not extending to costa; proximal laminal cells linear-rectangular, pitted, (45--)65--120(--150) ´ (13--)16--17(--19) µm; distal laminal cells shorter, narrow, pitted or with few pits, (20--)30--45(--60) ´ (5--)8--10(--13) µm. Sexual condition dioicous; male plants about as large as the female or slightly smaller; interior perichaetial leaves ± abruptly acuminate, convolute-sheathing. Seta 1.5--3 cm, solitary, rarely two per perichaetium, yellow to reddish brown. Capsule 1.5--3.5 mm, erect, straight or nearly so, furrowed when dry, brown; operculum 1.6--2.8 mm. Spores 13--19 µm.
Capsules mature in summer. Soil, soil over rock, peaty soil or rotten wood; 1600--3300 m; Ariz., Colo., N.Mex., Wyo.; Mexico (Chihuahua, Tamaulipas); West Indies (Dominican Republic); Central America (Guatemala).
An easily recognized species that occurs in the flora area only in the Rocky Mountains and the mountains of Arizona. It is the only species in the section Dicranum that has erect, straight to weakly arcuate capsules. Other important distinguishing features are the ovate-lanceolate, straight, obtusely acute, 1-stratose leaves with alar cells 1- or 2-stratose in part and the subpercurrent to percurrent costae that are smooth or weakly toothed on the abaxial surface near the leaf apex. Dicranum rhabdocarpum has been placed in the segregate genus Orthodicranum by J. M. Holzinger (1925) and other bryologists mainly because of its straight and erect capsules. However, it differs from taxa commonly placed in that genus, i.e., D. flagellare, D. fulvum, D. montanum, D. strictum and D. viride, by the elongate, pitted cells and the alar cells that are sometimes 2-stratose.