Dicranum
Sp. Musc. Frond., 126. 1801 ,.
Plants in loose to dense tufts, yellowish green to dark green, dull or shiny. Stems (0.5–)2–12(–18) cm, erect, simple or forked, densely tomentose with white or reddish brown, smooth to papillose rhizoids, these sometimes nearly absent, rhizoids arising at bases of branches (macronemata) and sometimes in rows scattered along stems (micronemata). Leaves usually lanceolate, rarely ovate, proximal part concave, rarely flat, distal subula keeled to tubulose, erect-appressed, erect-patent or spreading, straight, weakly curled, crispate or cirrate when dry, generally falcate-secund, less often straight, undulate, rugose or smooth; apices acute to obtuse, tips sometimes deciduous, apparently a means of asexual reproduction; margins plane to incurved or involute, entire to serrate in distal part, entire proximally; laminae 1- or 2-stratose at margins or sometimes near costa; laminal cells smooth; costa single, ending before apex to excurrent, smooth or toothed on abaxial surface, sometimes with 2–4 serrated ridges abaxially, 1–2 rows of guide cells, two well-developed stereid bands above and below, sometimes slightly differentiated or absent, extending to apex, or ending before the apex, adaxial and (or) abaxial epidermal layers of cells differentiated or undifferentiated, sometimes only a few cells in both layers enlarged; laminal cell walls weakly to strongly bulging, or bulges absent; leaf cells pitted or nonpitted, smooth or sometimes abaxially, rarely adaxially, mammillose, papillose or toothed by projecting cell ends, walls often thickened; distal and median laminal cells short or long, quadrate, rectangular or irregularly angled, proximal cells rectangular to linear, alar cells inflated, 1- or 2-stratose, rarely more, generally orange to brown, rarely poorly differentiated. Specialized asexual reproduction absent or as clusters of 1–6, deciduous, terete, flagelliform branchlets, borne in axils of distal leaves. Sexual condition dioicous or pseudomonoicous; male plants as large as female plants or dwarfed and epiphytic on stem rhizoids of female plants; perigonial leaves ovate, concave, short-acuminate; perichaetial leaves usually convolute-sheathing, abruptly subulate or rarely interior leaves gradually acuminate. Seta solitary or up to 6 per perichaetium, smooth, elongate, erect, twisted when dry, yellow, brown or reddish. Capsule erect or inclined, cylindric, straight or arcuate, smooth, striate or furrowed when dry, annulus of 1–3 rows of usually large, deciduous or persistent cells, sometimes indistinctly differentiated; operculum long-rostrate, straight or arcuate; peristome single, 16 teeth, split 1/3–1/2 their length into 2, rarely 3, divisions, vertically pitted-striolate proximally, papillose above, reddish brown. Calyptra cucullate, smooth, naked, covering most of capsule, fugacious. Spores 12–30 µm, spherical, finely papillose.
Distribution
North America, Mexico, West Indies, Central America, South America, Europe, Asia, Africa, Australia.
Discussion
Species ca. 140 (26 in the flora).
For this treatment the segregate Orthodicranum is not recognized. Whether to recognize that genus or not has been debatable for years. W. L. Peterson (1979) listed the following six characters that he considered important in separating it from Dicranum: (1) capsules straight vs. curved; (2) capsules smooth to slightly wrinkled vs. ribbed; (3) alar cells 1-stratose vs. 2-stratose; (4) peristome teeth relatively narrow (ca. 60 µm) vs. relatively wide (70–95 µm or more); (5) specialized asexual reproduction by broken leaf tips or flagellated branches common vs. rare; (6) specialized habitat of rocks and wood vs. habitat of wood or rock rare, usually on soil or humus. The species placed in Orthodicranum by him as well as by other bryologists are D. flagellare, D. fulvum, D. montanum, D. tauricum, and D. viride. Dicranum fragilifolium is another species in the flora area that also has been placed in Orthodicranum by some bryologists (e.g., J. Podpera 1954). The problem with recognizing that genus is that some of the members otherwise remaining in Dicranum share one or more of the six character states Peterson outlined for the segregate genus. Dicranum fragilifolium and D. rhabdocarpum are two of the species that commonly have some of the characters of Orthodicranum and some of those of Dicranum. Other species in Dicranum less commonly have characters of both genera. If for no other reason but the sake of utility it is more practical at this time to leave all the species in one genus so they can be keyed out together and compared more readily. Perhaps when a world monograph of Dicranum is done it will become more evident whether it is important to recognize Orthodicranum and perhaps even other segregate genera.
Leaf cross sections are necessary to observe cell features of the costa and laminal cells. The costa stereid and guide cells, the adaxial and abaxial epidermal cells, the number of layers of alar and laminal cells, and the bulges in the cell walls between the laminal cells are all observable in cross section. These characters are extremely important because they can reliably differentiate many species of Dicranum. The leaf cross section characters are usually less variable and less influenced by the environment than other gametophytic characters, such as leaf habit, shape, margins and costa length characters, and are utilized to a great extent since they are considered much more dependable in species identification than some of the other characters in the genus.
Excluded Species:
Dicranum subporodictyon (Brotherus) C. H. Gao & T. Cao (= Dicranodontium subporodictyon Brotherus)
Selected References
Lower Taxa
Key
| 1 | Leaves mostly straight, erect-spreading, the tips deciduous and absent | > 2 |
| 1 | Leaves rarely straight, usually crisped or falcate, the tips mostly present | > 4 |
| 2 | Costa without stereid bands, with 1-2 layers of cells above and below the guide cells in the basal part of the leaf; alar cells 1-stratose; capsule straight, erect. | Dicranum tauricum |
| 2 | Costa with stereid bands, although sometimes weak, with 2-3 layers of cells above and below the guide cells in the basal part of the leaf; alar cells 1- or 2-stratose; capsule straight and erect or arcuate | > 3 |
| 3 | Leaves shiny, with proximal cells pitted, distal cells rectangular, alar cells 2-stratose or with a few 1-stratose regions, lamina rarely with 2-stratose regions. | Dicranum fragilifolium |
| 3 | Leaves dull, with proximal cells not pitted (or with few pits), distal cells quadrate, alar cells 1-stratose or with few 2-stratose regions, lamina often with 2-stratose regions. | Dicranum viride |
| 4 | Distal leaf cells usually elongate, sinuose, pitted | > 5 |
| 4 | Distal leaf cells usually short (quadrate, rectangular, or irregularly angled), neither sinuose nor pitted (or with few pits) | > 14 |
| 5 | Costa with 2 rows of guide cells, without abaxial ridges; leaves 10-15 mm; setae often aggregate | Dicranum majus |
| 5 | Costa with 1 row of guide cells, often with abaxial ridges; leaves often less than 10 mm; setae solitary or aggregate | > 6 |
| 6 | Leaves keeled distally, margins strongly serrate to toothed in distal half; costa with 2-4 well-developed dentate ridges on abaxial surface in distal part of leaf | > 7 |
| 6 | Leaves tubulose to somewhat keeled distally, margins entire to serrate in distal half; costa without or with poorly developed dentate ridges distally on abaxial surface | > 9 |
| 7 | Leaves spreading, strongly undulate; setae aggregate, 3-6 per perichaetium. | Dicranum polysetum |
| 7 | Leaves falcate-secund, not or slightly undulate; setae solitary, rarely 2 per perichaetium | > 8 |
| 8 | Interior perichaetial leaves abruptly acuminate. | Dicranum scoparium |
| 8 | Interior perichaetial leaves gradually acuminate. | Dicranum howellii |
| 9 | Costa subpercurrent to percurrent; alar cells usually 1-stratose, rarely 2-stratose in part; capsule slightly arcuate to straight and erect | > 10 |
| 9 | Costa subpercurrent to excurrent; alar cells 2-stratose; capsule slightly to strongly arcuate | > 11 |
| 10 | Leaves spreading to slightly falcate-secund, margins serrate near apex; capsule 1.5-3.5 mm. | Dicranum rhabdocarpum |
| 10 | Leaves erect-spreading to erect-appressed, margins entire; capsule 1.5- 2 mm | Dicranum groenlandicum |
| 11 | Leaves with a long, narrow subula, apex acute to somewhat obtuse. | Dicranum spadiceum |
| 11 | Leaves with a short subula, apex obtuse to somewhat acute | > 12 |
| 12 | Leaves usually with twisted apex when dry; portion of some stems julaceous and composed of short, broad, concave, appressed, somewhat obtuse leaves; proximal leaf margins ± involute | Dicranum leioneuron |
| 12 | Leaves seldom or never with twisted apex when dry; without julaceous portions of stems; proximal leaf margins flat | > 13 |
| 13 | Leaves not or little rugose-undulate, dull, cells often somewhat rough on abaxial surface | Dicranum scoparium |
| 13 | Leaves rugose-undulate, shiny, cells smooth on abaxial surface. | Dicranum bonjeanii |
| 14 | Proximal leaf cells not pitted (or with few pits); alar cells usually 1-stratose, rarely 2-stratose; capsule generally straight; plants small, seldom more than 4 cm | > 15 |
| 14 | Proximal leaf cells pitted; alar cells 1- or often 2-stratose; capsule generally arcuate; plants large, often more than 4 cm | > 17 |
| 15 | Leaf lamina mostly 2-stratose above, costa usually more than 1/4 the width of leaf base. | Dicranum fulvum |
| 15 | Leaf lamina 1-stratose above, costa less than 1/4 the width of leaf base | > 16 |
| 16 | Plants without flagelliform branchlets; usually with weak, slender, brood branches with linear, strongly crisped leaves when dry; leaves semi-keeled distally and strongly papillose on abaxial surface, generally strongly cirrate when dry; distal leaf cells regularly quadrate. | Dicranum montanum |
| 16 | Plants with 2-6 flagelliform branchlets (rigid and terete branches with appressed leaves) in the distal leaf axils; brood branches absent; leaves tubulose distally and slightly papillose on abaxial surface, curled to crisped when dry; distal leaf cells short-rectangular to quadrate. | Dicranum flagellare |
| 17 | Leaves tubulose in distal half; costa often indistinct and scarcely prominent on abaxial surface | > 18 |
| 17 | Leaves keeled in the distal half; costa prominent and rounded on abaxial surface | > 21 |
| 18 | Leaf cells strongly papillose in distal half of leaf; costa without stereid bands in distal 1/4-1/3 of leaf, adaxial epidermal layer of cells gradually enlarged but not noticeably differentiated from cells below; capsule sometimes strumose, 1-3 per perichaetium; nw North America. | Dicranum pallidisetum |
| 18 | Leaf cells smooth or weakly papillose in distal half of leaf; costa with stereid bands in distal part of leaf as well as below, adaxial epidermal layer of cells noticeably enlarged and differentiated from stereid cells below; capsule not strumose, solitary; across North America | > 19 |
| 19 | Leaves cirrate to crisped when dry; distal leaf cells short-rectangular to quadrate, with thin walls, proximal cells 9-12 µm wide; costa with adaxial epidermal layer of cells enlarged (seen in cross section near leaf middle); capsule 2-4 mm. | Dicranum muehlenbeckii |
| 19 | Leaves erect-appressed or slightly curled when dry; distal leaf cells elliptical to rectangular, with thick walls, proximal cells 5-6 µm wide; costa with only a few cells in adaxial epidermal layer enlarged; capsule 1-2 mm | > 20 |
| 20 | Proximal leaves with acute apices; proximal leaf cells usually less than 40 µm, median cells pitted mainly proximal to middle of leaf. | Dicranum elongatum |
| 20 | Proximal leaves often with blunt apices; proximal leaf cells usually more than 40 µm, median cells pitted well beyond middle of leaf. | Dicranum groenlandicum |
| 21 | Leaves plane or indistinctly undulate near apex | > 22 |
| 21 | Leaves undulate or rugose (D. condensatum indistinctly undulate) | > 24 |
| 22 | Leaves strongly cirrate to crisped when dry, proximal cells usually less than 45 µm; cells walls between lamina cells strongly bulging as seen in cross section; capsule 2-4 mm | Dicranum brevifolium |
| 22 | Leaves straight to ± curled when dry, proximal cells usually more than 45 µm; cell walls smooth or only slightly bulging between lamina cells as seen in cross section; capsule mostly 1-3 mm | > 23 |
| 23 | Leaves with distal margins ± involute, laminae with few 2-stratose regions on margins in the distal part; leaf cells smooth to slightly papillose on abaxial surface in distal part of leaf | Dicranum acutifolium |
| 23 | Leaves with distal margins erect, laminae with one or both distal margins 2-stratose; leaf cells papillose on abaxial surface in distal part of leaf. | Dicranum fuscescens |
| 24 | Costa ending well before apex, rarely nearly percurrent. | Dicranum undulatum |
| 24 | Costa percurrent to excurrent | > 25 |
| 25 | Leaves erect-spreading to erect and compressed when moist; distal-median leaf cells irregularly angled, with unequally thickened walls | > 26 |
| 25 | Leaves falcate-secund when moist; distal-median leaf cells short-rectangular to quadrate, with equally thickened walls | > 28 |
| 26 | Leaves gradually narrowed to a long-acuminate apex; costa with a few differentiated cells in adaxial epidermal layer, cell walls between lamina cells not bulging. | Dicranum drummondii |
| 26 | Leaves acute to gradually narrowed to a short-acuminate apex; costa absent differentiated cells in adaxial epidermal layer, cell walls between lamina cells weakly to strongly bulging | > 27 |
| 27 | Leaves broadly lanceolate, not arched, slightly crisped when dry, not imbricate | Dicranum condensatum |
| 27 | Leaves ovate to ovate-lanceolate, concave and arched, loosely imbricate when dry | Dicranum spurium |
| 28 | Leaf margins strongly toothed distally, laminae with toothlike projections scattered distally on abaxial surface; setae often aggregate, (1-)2-5 per perichaetium; capsule not strumose. | Dicranum ontariense |
| 28 | Leaf margins slightly serrate distally, laminae smooth to slightly rough distally on abaxial surface; seta always solitary; capsule ± strumose | > 29 |
| 29 | Leaves strongly crisped to cirrate when dry, proximal leaf cells usually less than 45 µm; stems densely tomentose. | Dicranum brevifolium |
| 29 | Leaves straight to curled when dry, proximal leaf cells often more than 45 µm; stems somewhat tomentose. | Dicranum acutifolium |