Dicranum
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Dicranum  |
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Family: Dicranaceae Media not available |
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 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 ut
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