Muehlenbeck's Dicranum Moss

Dicranum muehlenbeckii is a somewhat rare species throughout North America, where it is often misidentified as other species of the genus. There should be no reason for its misidentification if its important characters are utilized for recognition. Smooth, erect-spreading leaves, cirrate to crisped when dry and tubulose above, smooth leaf cells, 1-stratose laminae, and cross section of the costa showing the abaxial and adaxial rows of cells differentiated, all combine to make the gametophytes different from all other North American species of the genus. Sporophytes are rarely produced but the 2-4 mm, solitary, long-cylindric, slightly strumose capsules, which are suberect to slightly arcuate and weakly striate when dry, are distinctive.

Plants medium-sized, 2–4 cm high, yellowish green or brownish green, not or somewhat shiny, in compact tufts. Stems erect or ascending, simple or branched, tomentose below. Leaves crispate when dry, erect-patent or slightly secund when moist, ovate-lanceolate, 8–10 mm × 1 mm, gradually narrowed from an oblong-ovate base to slender, or subulate, channeled acumen; margins plane below, involute above, double-toothed and bistratose in the upper part; costa stout, occupying 1/5– ¼ the leaf base width, percurrent or shortly excurrent, not particularly ridged at back, smooth or somewhat serrulate near the tips; upper cells quadrate to rounded quadrate, incrassate, not porose, somewhat mammillose at back; basal cells elongate, rectangular, thick-walled, porose; alar cells quadrate, slightly inflated, bistratose, deeply brownish. Dioicous. Male plants dwarfed. Setae single or sometimes two per perichaetium, straight, 2.5–3.0 cm long, yellowish; capsules cylindric, curved, urns ca. 3 mm long, sometimes strumose at base, more or less furrowed when dry and empty; opercula obliquely long-rostrate, ca. 2 mm long; annuli in 1 or 2 rows of large cells, deciduous; peristome teeth lanceolate, divided to the middle, reddish brown, papillose above, vertically striolate below. Spores 18–20 µm in diameter, minutely papillose.

Plants in dense tufts, green to yellowish green, dull. Stems 3-7 cm, densely tomentose with reddish brown rhizoids. Leaves erect-spreading, strongly cirrate to crisped when dry, smooth, (4-)5-6.5(-8) × 0.5-1 mm, concave below, tubulose above, lanceolate, acute; margins entire below, slightly serrate to entire above; laminae 1-stratose; costa excurrent, ¹/6-¹/4 the width of the leaves at base, smooth or weakly toothed above on abaxial surface, abaxial ridges absent, with a row of guide cells, two stereid bands extending to the apex, adaxial and abaxial epidermal layers of cells differentiated; cell walls between lamina cells slightly bulging; leaf cells smooth to slightly rough above on abaxial surface; alar cells 2-stratose, differentiated, sometimes extending to costa; proximal laminal cells rectangular, pitted, (19-)37-55(-73) × (5-)9-12(-14) µm; distal laminal cells short, irregularly quadrate-rectangular, not pitted, (7-)11-12(-23) × (6-)8-9(-13) µm. Sexual condition pseudomonoicous; dwarf males on stem rhizoids of female plants; interior perichaetial leaves abruptly short-acuminate, convolute-sheathing. Seta 1.3-3 cm, solitary, yellowish to yellowish brown. Capsule 2-4 mm, long-cylindric, arcuate and inclined to ± straight and nearly erect, smooth, striate when dry, yellowish brown; operculum 1.5-2.5 mm. Spores 14-24 µm.

Distribution: China, Korea, Japan, Europe, Russia, and North America.

Habitat: on humic soil or rocks.

Dicranum neglectum auct. non Jur. ex De Not., Atti Reale Univ. Genova 1: 613. 1869. Dicranum muehlenbeckii var. neglectum auct. non (De Not.) Pfeff., Neue Denschr. Schweiz. Naturf. Ges. 4: 23. 1869. Dicranum spadiceum auct. non Zett., Kongl. Svenska Vetensk. Acad. Handl. 5(10): 20. 1865.