Dicranum polysetum
Dicranum fragilifolium
dicranum moss, wavy broom moss, wavy-leaf heron's-bill moss, wavy-leaf moss
fragile leaf dicranum moss
4–15 cm, densely tomentose with whitish or reddish rhizoids.
1.5–6 cm, densely tomentose with dark brown to red rhizoids.
erect to spreading, ± flexuose, little changed when dry, strongly undulate, (5.5–)7–9.5(–10.5) × 1–2 mm, lanceolate, concave proximally, keeled above, acute;
margins strongly toothed in the distal half;
laminae 1-stratose;
costa ending before apex, occupying ca. 1/16–1/8 of leaf base, strong, with two toothed ridges distally on abaxial surface, with one row of guide cells, two stereid bands, adaxial epidermal layer of cells not differentiated, abaxial layer with a few cells enlarged;
cell walls between lamina cells not bulging;
leaf cells smooth;
alar cells 2-stratose, well-differentiated, not extending to costa;
proximal laminal cells elongate, pitted, (45–)78–129(–156) × (5–)9–10(–14) µm;
distal laminal cells shorter, sinuose, pitted, (42–)64–68(–115) × (4–)9–10(–13)µm. Sexual condition pseudomonoicous;
dwarf male plants on stem rhizoids of female plants;
interior perichaetial leaves abruptly long-acuminate, convolute-sheathing.
straight, erect-spreading, rigid, appressed when dry, smooth, (5–)6–7(–7.5) × 0.4–0.6 mm, most of the leaf tips deciduous and absent, concave proximally, canaliculate distally, from a lanceolate base to a long subula formed by the excurrent costa, apex acute;
margins entire to somewhat serrulate above;
laminae 1-stratose or some 2-stratose regions near costa;
costa excurrent, 1/4–1/3 the width of the leaves at base, smooth or slightly rough above on abaxial surface, abaxial ridges absent, with a row of guide cells, two thin stereid bands (2–3 cells thick), adaxial and abaxial epidermal layers not differentiated or sometimes with a few cells in both layers enlarged;
cell walls between lamina cells slightly bulging;
leaf cells smooth;
alar cells 1-stratose, sometimes with some 2-stratose regions, well-differentiated, sometimes extending to costa;
proximal laminal cells elongate-rectangular, usually pitted or indistinctly pitted, (25–)39–55(–84) × (5–)7–8(–10) µm;
median laminal cells rectangular, not pitted, (11–)21–22(–37) × (4–)7–8(–10) µm;
distal laminal cells nearly elliptic, incrassate.
1.5–4 cm, usually aggregate, 3–6 per perichaetium, brown or reddish brown.
1.5–2.5 cm, solitary, yellowish to brown.
dioicous;
male plants as tall as females, usually more slender;
interior perichaetial leaves abruptly long-acuminate, convolute-sheathing.
2–3.5 mm, arcuate, inclined to horizontal, furrowed when dry, yellowish brown or reddish brown;
operculum 2–4 mm.
1.8–2 mm, arcuate to nearly straight, ± erect, smooth, sometimes striate when dry, yellowish brown;
operculum 1–2 mm.
12–24 µm.
16–28 µm.
Dicranum polysetum
Dicranum fragilifolium
W. L. Peterson (1979) recorded Dicranum polysetum from Nunavut. It is one of the largest, most conspicuous, and most easily recognized species in the genus in North America. The species is immediately recognized by the large stems, 4–15 cm, with a dense mat of whitish or reddish tomentum, giving the stems a thickened appearance, by the shiny, strongly undulate, wide-spreading leaves with margins strongly toothed in the distal half and by the clustered sporophytes (3–6 per perichaetium). Microscopically, the species is readily distinguished by the elongate, abundantly pitted cells throughout the leaf and by the toothed ridges on the abaxial surface of the costa in the distal part of the leaf. Dicranum polysetum is one of the few species in North America that has no apparent intergradations with any other species of the genus. It is common in southeastern Canada, northeastern United States, and the Canadian Rocky Mountains, where it extends south to Wyoming and Colorado, occurring in both states in a small number of localities. It is rare west of the Rockies, where it is known from only a few localities in northwestern Montana, southern Idaho and northeastern Washington and Oregon.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Dicranum fragilifolium is a rare boreal species with shiny, light green to yellowish brown, erect-spreading leaves. The distal portion of the leaves is fragile and often broken off, thereby giving the plants a distinctive appearance. The deciduous leaf apices presumably serve as a type of asexual reproduction by regenerating to produce new plants. The species is often confused with D. tauricum, another species with deciduous leaf tips, but the latter occurs only in western North America. Where their ranges overlap they frequently are difficult to tell apart. When sporophytes are present the straight capsules of D. tauricum are distinctive from the usually arcuate ones of D. fragilifolium, which unfortunately rarely produces them. When sterile, the best way to separate the two is by the costa cross section in the proximal half of the leaf: D. fragilifolium has stereid cells in two thin bands while D. tauricum has none. Also, in D. fragilifolium there are 2–3 layers of cells above and below the guide cells, while in D. tauricum there are 1 or rarely 2 layers of cells. One other species with deciduous leaf tips that has sometimes been confused with D. fragilifolium is D. viride of eastern North America. It has a straight capsule like D. tauricum but as in D. fragilifolium capsules are rarely produced. The broad costa of D. viride, covering 1/3 or more of the leaf base, will distinguish it from D. fragilifolium, the costa of which covers 1/4 or less of the leaf base.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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