Published In:
Species Muscorum Frondosorum 183, pl. 42, f. 8–12. 1801. ( Sp. Musc. Frond.)   
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(Last Modified On 2/22/2011)
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Acceptance
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Accepted
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(Last Modified On 2/22/2011)
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Discussion:
Bryum dichotomum is a
widespread, weedy species better known in the Northern Hemisphere as B.
bicolor. It is a small Bryum with short, broad leaves that are not
or scarcely bordered, a stoutly excurrent costa and short, thick‑necked,
purple‑red capsules. It has firm-walled leaf cells that are elongate
above but quadrate below.
There are three other Central
American species (B. argenteum, B. chryseum, and B.
leptocladon) similar to B. dichotomum in size and leaf shape. Bryum
argenteum differs from B. dichotomum in its silvery color, while B.
chryseum differs in having long, slender capsules and quadrate stem
epidermal cells. The presence of thin‑walled, rectangular basal leaf
cells and percurrent to very short‑excurrent costae in Bryum
leptocladon separates it from B. dichotomum. Bryum coronatum
and B. dichotomum are similar in capsule shape and in having
weakly limbate leaves. The larger plant size and lax, thin-walled leaf cells
that are short above but short‑rectangular at base will separate B.
coronatum from B. dichotomum.
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Illustrations:
(mostly as B.
bicolor). Hedwig (1801, 42 8–12); Bruch and Schimper (1839, Pls. 378–379,
as B. atropurpureum and B. versicolor); Sullivant (1856, Pls.
6–7, as B. californicum and B. occidentale); Dixon and Jameson
(1896, Pl. 45 H, as B. atropurpureum); Brotherus 1923, Fig. 53 F–G);
Nyholm (1958, Fig. 138); Breen (1963, Pl. 62 5–7); Ochi (1970, Figs. 5–9);
Lawton (1971, Fig. 90 1–7); Ochi (1972, Fig. 33); Flowers (1973, Pl. 82 1–8);
Gangulee (1974, Fig. 485); Smith (1978, Fig. 199 1–4); Catcheside (1980, Fig.
158); Crum and Anderson (1981, Fig. 262); Orbán and Vajda (1983, Fig. 387);
Reese (1984, Fig. 37 C–E); Magill (1987, Fig. 103 21–28); Noguchi (1988, Fig.
211 A); Nyholm (1993, Fig. 181); Sharp et al. (1994, Fig. 345 f–k);
Allen (1995 Fig. 5); Jóhannsson (1995, Figs. 103–105); Churchill and Linares
(1995, Fig. 26 a–c). Figure 143 A–H.
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Habitat:
On moist bank; 1050–1350
m.
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Distribution in Central America:
BELIZE. Cayo: Allen 18177I (BRH, MO). NICARAGUA. Jinotega: Standley
10300 (F, MO).
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World Range:
Western and Eastern
Canada, Northwestern, North‑Central, Northeastern, Southwestern, South‑Central,
and Southeastern U.S.A.; Mexico; Central America; Western and Southern South
America, Brazil; Subantarctic Islands; Northern, Middle, East, Southwestern,
and Southeastern Europe; Russian Far East, Caucasus, Middle Asia, China,
Eastern Asia, Western Asia, Arabian Peninsula; Macaronesia, Northern Africa,
Northeast, East, and South Tropical Africa, Southern Africa, Western Indian
Ocean; Indian Subcontinent, Malesia; Australia, New Zealand; Southwestern
Pacific.
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Bryum dichotomum Hedw., Sp. Musc. Frond. 183. 1801.
Protologue: New Zealand. Nova Seelandia, s. coll.
Bryum bicolor Dicks., Pl. Crypt. Brit. 4: 16. 1801. Protologue: Great Britain. In arenosis gramineis, s. coll.
Plants small, green to yellow‑green in loose tufts to 2 mm high; rhizoids dense at base. Leaves 1–1.7 mm long, erect‑imbricate, firm when dry, erect‑spreading when wet, ovate to ovate‑lanceolate; apices acuminate; margins recurved below, not or indistinctly bordered, entire; costae short to long‑excurrent; upper cells elongate-rhomboidal, thick‑walled, to 60 μm long, basal cells quadrate, occasionally short‑rectangular, firm‑walled, 16–28 μm long. At times with bud‑like, axillary gemmae or rhizoidal tubers. Dioicous. Setae 5–10 mm long, red or purple. Capsules 1–3 mm long, dark‑red, pendent, obovate to oblong-cylindrical, neck short, somewhat broader than the urn; annuli compound and revoluble; opercula 0.5 mm long, conic apiculate; exostome teeth yellow‑brown, densely papillose, endostome yellowish hyaline, lightly papillose, basal membrane to ½ of exostome teeth length, segments well-developed, broadly perforate, cilia 2–4, nodose to appendiculate. Spores 8–12 μm, lightly roughened. Calyptra not seen.
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