Dicranum acutifolium
Dicranum howellii
acuteleaf dicranum moss, sharp-leaf heron's-bill moss
Howell's broom moss, Howell's dicranum moss
1.5–7 cm, generally branched above, somewhat tomentose with reddish brown rhizoids.
2–8 cm, densely tomentose with white to 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.
falcate-secund to straight and erect, sometimes slightly crisped, smooth, (5–)8–10(–12) × 0.8–1.5 mm, concave proximally, keeled or tubulose above, lanceolate, apex acute;
margins strongly serrate in the distal part, entire proximally;
laminae 1-stratose;
costa ending before apex to shortly excurrent, 1/12–1/5 the width of the leaves at base, with 2, rarely 4, toothed ridges on the abaxial surface extending from about the leaf middle nearly to the apex, rarely almost smooth, with a row of guide cells, two thin stereid bands, adaxial epidermal layer of cells not differentiated, the abaxial layer interrupted by several enlarged cells that form part of the abaxial ridge, not extending to the apices;
cell walls between lamina cells not bulging;
leaf cells smooth;
alar cells 2-stratose, well-differentiated, sometimes extending to costa;
proximal laminal cells linear-rectangular, pitted, (52–)65–105(–120) × (10–)12–18(–22) µm;
distal laminal cells shorter, sinuose, pitted, (42–)54–90(–108) µm × (10–)12–14(–16) µm. Sexual condition pseudomonoicous or dioicous;
dwarf males on rhizoids of female plants or male plants as large as females and growing intermixed or in ± separate tufts;
perichaetial leaves gradually acuminate, not or partially convolute-sheathing.
1.2–2.5 cm, solitary, yellow to reddish yellow.
1.5–4 cm, solitary, sometimes 2 per perichaetium, yellow to reddish 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.
2–3.8 mm, arcuate, inclined to horizontal, smooth to striate when dry, yellow to dark reddish brown;
operculum 2–3.8 mm.
14–28 µm.
18–26 µm.
Dicranum acutifolium
Dicranum howellii
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 howellii occurrs only in the northwestern part of North America. It is closely related to the common and nearly ubiquitous D. scoparium. The shape of the interior perichaetial leaves is the most reliable way to distinguish the two. Gradually acuminate perichaetial leaves that loosely surround the seta are characteristic of D. howellii. Dicranum scoparium has abruptly acuminate exterior perichaetial leaves, interior ones that are abruptly acuminateto blunt at the apex and are convolute-sheathing around the seta. The interior perichaetial leaves of D. howellii are also longer and narrower than those of the D. scoparium. Other less significant features of D. howellii are the consistently glossy, long leaves, mostly 8–10 mm, with long distal cells, averaging 54–90 µm, and the common occurrence of only two, rarely four, serrated ridges on the abaxial surface of the costae. Dicranum scoparium by comparison has glossy to sometimes dull leaves that are often shorter, mostly 5–8.5 mm, with shorter distal cells, averaging 27–43 µm, and the costae usually have four, rarely two, serrated ridges on the abaxial surface. The perichaetial leaves are undoubtedly the most important feature separating the two species, as well as being the easiest to observe. Eastern North American plants of D. scoparium all have the abruptly acuminate perichaetial leaves that are characteristic of the species, as do plants elsewhere in the world. The perichaetial leaf character was one reason D. howellii was believed to be a distinct species by F. Renauld and J. Cardot (1889, plate 12B) who first illustrated that character and this remains the most significant reason for maintaining it as a distinct species.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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USDA Plants Database
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