Dicranum acutifolium
Dicranum muehlenbeckii
acuteleaf dicranum moss, sharp-leaf heron's-bill moss
muehlenbeck's dicranum moss
1.5–7 cm, generally branched above, somewhat tomentose with reddish brown rhizoids.
3–7 cm, densely tomentose with reddish brown rhizoids.
erect-spreading, slightly curled to ± straight when dry, usually with a few undulations in distal part, (3.5–)5–8(–10) mm × 0.5–1 mm, concave below, keeled above, sometimes margins ± involute, lanceolate, narrowly acute to acuminate;
margins serrulate to serrate above;
laminae 1-stratose or with few 2-stratose regions on or near the distal margins;
costa percurrent to shortly excurrent, 1/6–1/4 the width of the leaves at base, smooth to slightly papillose above on abaxial surface, abaxial ridges absent, with a row of guide cells, two stereid bands extending to the apex, adaxial epidermal layer of cells not differentiated, the abaxial layer differentiated;
cell walls between lamina cells not or slightly bulging;
leaf cells smooth to weakly papillose above on abaxial surface;
alar cells 2-stratose, differentiated, often extending to costa;
proximal laminal cells linear-rectangular, pitted, (22–)41–60(–90) × (5–)6–8(–12) µm;
distal laminal cells short-rectangular, irregularly angled or rounded, not pitted, (7–)12–20(–32) × (4–)8–9(–14) µm. Sexual condition pseudomonoicous;
dwarf males on stem rhizoids of female plants;
interior perichaetial leaves abruptly short-acuminate, convolute-sheathing.
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.
1.2–2.5 cm, solitary, yellow to reddish yellow.
1.3–3 cm, solitary, yellowish to yellowish brown.
2–2.7 mm, arcuate, inclined to horizontal, furrowed when dry, rarely slightly strumose, brown to reddish brown;
operculum 1.5–2.5 mm.
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.
14–28 µm.
14–24 µm.
Dicranum acutifolium
Dicranum muehlenbeckii
Dicranum acutifolium has been reported from Colorado by W. A. Weber (1973), but has been deleted from the flora (Weber, pers. comm.). It has also been reported from New Mexico, New York, and Wyoming by W. L. Peterson (1979). This arctic-alpine species is recognized by its erect-spreading leaves, slightly curled when dry, keeled and often weakly undulate above, lanceolate, narrowly acute to acuminate, by its percurrent to shortly excurrent costae, smooth to slightly papillose above, and by its leaf cross section that shows only the abaxial row of cells differentiated, a few 2-stratose marginal cells and the cell walls between lamina cells smooth to slightly bulging. Dicranum acutifolium has often been confused with D. fuscescens but the latter species has a longer, rougher subula that in leaf cross section in the distal half reveals very large and obvious papillae, compared to the smaller and less distinct ones in the former, and margins that are almost completely 2-stratose, while those of D. acutifolium are mostly 1-stratose. It has also been confused with 13. D. brevifolium and for distinctions see discussion thereunder.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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