Dicranum sulcatum Kindb. in Mac. according to Index Muscorum a Hom Illeg.
Bull. Torr. Bot. Club 17: 87. 1890.
Plants in lustreless green to olive green or brownish cushions or tufts, to 8 cm high. Leaves consistently falcate secund, somewhat crispate when dry, not at all undulate, erect spreading when moist, grooved to subtubulose distally, to 8 mm long, 5–6: 1, neither plicate nor fragile, narrowly lanceolate. Distal juxtacostal cells prorate papillose with prorae to 10 µm high, to 15 µm wide, 1–2: 1, not in regular rows, gradually reduced in size and becoming isodiametric toward margins. Basal cells rectangular, to 20 µm wide, more strongly pitted than median cells. Alar region well demarcated, mostly not extending to costa. Alar cells to 30 µm broad, quadrate to short rectangular, inflated, rather thin walled. Supra-alar cells rectangular, to 15 µm broad, to 5: 1, arranged in regular rows. Costa percurrent to excurrent in a mostly acute apex, without abaxial ridges. Costa cross-section with two stereid bands and with a single layer of guide cells but with only a dorsal epidermis. Margin plane to erect, serrate to geminate serrate at least near apex, distally bistratose. Rhizoids pale brown, to 35 µm wide at base, smooth. Stem cross-section with central strand obscure, and with small and pachydermous outer cortical cells surrounding large and leptodermous inner cells.
Usually pseudautoicous with male plants bud-form, in the axils of leaves close to the perichaetia. Perichaetial leaves convolute and partially sheathing base of seta, truncate into a short acumen. Usually monosetous with the seta to 20 mm, yellow to brownish, straight and smooth. Urn inclined to horizontal, arcuate, strongly sulcate, to 2.5 mm long, 2.5–4: 1, obscurely to not at all strumose. Operculum rostrate, about 2/3 as long as urn. Annulus of about two rows of thin walled, deciduous cells. Exothecial cells to 30 µm wide, 2–4: 1, not in regular vertical rows, quite irregular in size and shape, irregularly rectangular with neither the lateral nor the transverse walls parallelling one another, thick walled and pitted, with strong corner thickenings. Cells near mouth of capsule reduced in size, rounded isodiametric in 2–5 rows. Stomata present on base of urn. Peristome red-brown, inserted near capsule mouth, to 700 µm long, bifid to near the middle, lanceolate with filiform apices, vertically striate proximally but at least somewhat papillose distally, smooth or nearly so at least proximal portion of ventral plate. Spores papillose, to 22 µm.
This with D. fuscescens is one of that large group of sibling species pairs in which one species (D. sulcatum) is primarily on undisturbed habitats while the other (D. fuscescens) is on disturbed sites. D. sulcatum is primarily a coastal species which reaches its best development on the bark of Sequoia sempervirens and associated trees in perennially humid sites at low elevations.