Dicranum scoparium
Dicranum flagellare
broom heron's-bill moss, broom-moss, dicranum moss
dicranum moss, whip fork moss, whip heron's-bill moss
2–10 cm, tomentose with white to brown rhizoids.
0.5–6 cm, densely tomentose with light brown to reddish brown rhizoids.
very variable, usually falcate-secund, rarely straight and erect, slightly contorted and crisped when dry, sometimes slightly rugose or undulate, (4–)5–8.5(–15) × 0.8–1.8 mm, concave proximally, keeled above, lanceolate, apex acute to somewhat obtuse;
margins strongly serrate in the distal 1/3 or rarely slightly serrulate;
laminae 1-stratose;
costa percurrent, excurrent, or ending before apex, 1/10–1/5 the width of the leaves at base, usually with 2–4 toothed ridges above on abaxial surface, 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, (25–)47–100(–132) × (5–)7–12(–13) µm;
distal laminal cells shorter, broad, sinuose, pitted, (11–)27–43(–53) × (5–)8–12(–20) µm. Sexual condition pseudomonoicous or dioicous;
dwarf males on rhizoids of female plants or male plants as large as females;
interior perichaetial leaves abruptly long-acuminate, convolute-sheathing.
falcate-secund to nearly straight, crisped to weakly crisped when dry, smooth, (1–)2–4(–5) × 0.3–0.6 mm, concave below, tubulose above, from a lanceolate or ovate-lanceolate base to an acuminate subula, apex acute;
margins smooth to serrulate above;
laminae 1-stratose;
costa percurrent or sometimes ending just before apex, 1/6–1/4 the width of the leaves at base, smooth to ± rough with papillae or small teeth on abaxial surface near apex of leaf, abaxial ridges absent, with a row of guide cells, two stereid bands above and below not extending above the leaf middle, adaxial epidermal layer of cells not differentiated, the abaxial layer with some cells differentiated;
cell walls between lamina cells not bulging;
leaf cells smooth or weakly abaxially prorate above;
alar cells 1-stratose, distinctly differentiated, not extending to costa;
proximal laminal cells elongate-rectangular, not pitted or with few pits, (12–)24–38(–70) × (4–)10–15(–18) µm;
distal laminal cells short-rectangular to quadrate, not pitted, (5–)12–14(–23) × (5–)7–12(–14) µm. Sexual condition dioicous;
male plants as large as females;
interior perichaetial leaves abruptly long-acuminate, convolute-sheathing.
2–4 cm, solitary, rarely two per perichaetium, yellowish brown to reddish brown.
1–2.5 cm, solitary, yellowish to brown.
2.5–4 mm, arcuate, inclined to horizontal, smooth to striate when dry, yellowish brown to reddish brown;
operculum 2–3.5 mm.
1.5–3 mm, straight and erect or nearly so, striate when dry, yellowish brown to brown;
operculum 0.5–l.6 mm.
14–24 µm.
12–19 µm.
Dicranum scoparium
Dicranum flagellare
Dicranum scoparium is undoubtedly the most polymorphic species of the genus in North America. It is commonly called the broom moss because the leaves are “swept” or turned in the same direction. However, the habit of the leaves varies from strongly falcate-secund, i.e., the swept state, to straight and erect, especially prevalent in northern plants. The leaf shape varies from the typical lanceolate and long-acuminate to the odd ovate-lanceolate and short-acuminate. The leaves are typically smooth, in sharp contrast to the strongly undulate leaves of D. polysetum, but on rare occasion they can be somewhat undulate-rugose. The leaf margins are usually distinctly toothed in the distal 1/3 but at times plants in some populations have extremely weak serrations, appearing nearly entire. The costae vary in extent from subpercurrent to shortly excurrent. The abaxial surface of the costae have two to four toothed ridges, compared to the two in D. polysetum, but in some forms they are almost nonexistent. The distal areolation of the leaves seems to remain constant in the myriad forms of D. scoparium, the cells being short-sinuose with pitted walls, generally containing conspicuous oil-drops.
Plants growing in arctic North America and those in extremely wet habitats, such as bogs, often have a different superficial appearance. The leaves are straight, erect, ovate-lanceolate, short-acuminate with weak serrations on the margins, and the abaxial ridges on the costae are poorly developed. Sometimes the plants have distal shoots with abnormal appearing leaves that are shorter and broader than those below. Some of these collections have been referred to Dicranum latifolium, which I consider to be a synonym of D. scoparium. Further field and laboratory studies are required to clarify the taxonomic status of those plants. In the sterile state, large-leaved plants of D. scoparium can be confused with D. majus. The latter is immediately distinguished by a double row of guide cells, instead of the single row in the former, thicker stereid bands, distal cells that are narrower and more elongate and costae that have small teeth or serrulations distally on the abaxial surface instead of the characteristic 2–4 toothed ridges of D. scoparium. When fruiting, the solitary, rarely paired, sporophytes of D. scoparium distinguish it from D. majus, which has multiple sporophytes, 2–5 per perichaetium.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Dicranum flagellare has been reported from Northwest Territories by W. L. Peterson (1979) and Arizona by I. M. Haring (1961). It is easily recognized because of the presence of unique axillary, flagelliform branchlets, in clusters of 2–6, which some plants in each colony almost always possess. The branchlets are deciduous and represent another type of asexual reproduction present in species of Dicranum, e.g. deciduous branchlets with linear, crisped leaves in D. montanum, and deciduous leaf tips in D. fragilifolium, D. tauricum and D. viride. C. E. Correns (1899) discussed the flagelliform branchlet type of asexual reproductive in D. flagellare as well as the other types of asexual reproduction occurring in the genus. The only species likely to be confused with D. flagellare if the flagelliform branchlets are overlooked or cannot be found is 25. D. montanum. For distinctions see the discussion under that species.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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