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Moss China | Family List | Moss China V. 2 | Pottiaceae

9. Didymodon Hedw., Sp. Musc. Frond. 1801.


Plants small to rather robust, usually growing on calcareous soil or rocks, brownish green to reddish brown, in loose or dense tufts. Stems erect, simple or sometimes branched; central strand present, rarely absent. Leaves appressed or contorted when dry, erect-spreading to squarrose-recurved when moist, ovate-lanceolate or broadly lanceolate; margins entire or occasionally crenulate, narrowly revolute; costa strong, percurrent or excurrent, or occasionally ending below the apex, ventral cells of costa narrowly elliptic or rounded quadrate, in cross section with 2 stereid bands; upper leaf cells rounded to rounded quadrate or rhombic, somewhat thick-walled, smooth or bluntly papillose, cell outlines clear; basal cells firm, shortly rectangular to oblong-ovate or rounded quadrate, light green to brownish. Gemmae sometimes present in specialized rhizoids or in leaf axils. Dioicous. Perichaetial leaves similar to stem leaves or slightly differentiated. Setae elongate, erect, reddish brown at the base, yellowish brown at the upper part; capsules erect, oblong-ovoid or cylindrical; annuli not differentiated or in 1–3 rows of cells; opercula shortly rostrate; peristome teeth with a low basal membrane, 16 undivided or split into 32 linear, straight or twisted counterclockwise, densely papillose, occasionally peristome teeth absent. Calyptrae cucullate, smooth, naked. Spores spherical, yellowish green.

Some authors (Hilpert 1933, P.-C. Chen et al. 1963, X.-J. Li 1985, 1996) submerged Didymodon in Barbula. However, others (Saito 1975, Crum & Anderson 1981, Zander 1993) separated Didymodon from Barbula on the basis of axillary rhizoids, shape and color of basal leaf cells, and the peristome teeth. Barbula has low and twisted peristome teeth above a low basal membrane, while Didymodon has shorter and erect or merely inclined peristome teeth. We recognize the genus Didymodon in this study. Nineteen species and one variety are found from China. Didymodon gaochienii B. C. Tan & Y. Jia was recently described as new from Qinghai, China (Tan & & Jia 1997). Didymodon subandreaeoides (Kindb.) Zand. was reported from Tibet, China by T. Cao and C. Gao (1995) based on Andreaea kashyapii Dix. ex Vohra & Wadhwa. These two species are not included in this treatment.

1 Costa slender, ending at or below the leaf apex; leaf cells smooth or unipapillose   (2)
+ Costa stout, percurrent or excurent; leaf cells multi-papillose or sometimes unipapillose   (3)
2 (1) Leaves triangular-lanceolate; costa ending well below the apex; leaf cells smooth; capsules ovoid   16 Didymodon rufidulus
+ Leaves ovate-lanceolate; costa ending at the apex; leaf cells usually unipapillose; capsules cylindrical   15 Didymodon rivicolus
3 (1) Leaves short and broad, usually broadly ovate to oblong-ovate or ligulate, blunt or rounded at the apex   (4)
+ Leaves narrowly ovate, triangular or linear-lanceolate, gradually acute or acuminate   (7)
4 (3) Plants only ca. 0.5 cm high; leaves imbricate, broadly ovate at the base   13 Didymodon perobtusus
+ Plants (1.0-)2.5-6.0 cm high; leaves spreading, narrowly oblong-ovate at the base   (5)
5 (4) Plants bright green; leaf apex broad and rounded, slightly cucullate   18 Didymodon tophaceus
+ Plants reddish brown; leaf apex narrowly and acuminate, not cucullate   (6)
6 (5) Cells of the abaxial surface of costa linear-oblong, walls slightly sinuate; upper leaf cells smooth, or occasionally with 1 indistinct low papilla   10 Didymodon japonicus
+ Cells of the abaxial surface of costa quadrate to short-rectangular, walls not sinuate; upper leaf cells usually with 1 blunt papilla   11 Didymodon nigrescens
7 (3) Leaves squarrose when moist; leaf cell walls strongly and irregularly thickened   (8)
+ Leaves erect-spreading when moist; leaf cell walls not particularly thickened   (15)
8 (7) Leaf bases very broad, deltoid, narrowly lanceolate toward the apex; basal cells linear, very thick-walled, sinuose because of porose walls   9 Didymodon giganteus
+ Leaf bases ovate-lanceolate; basal cells shortly rectangular, slightly thick-walled, not porose   (9)
9 (8) Leaf apices shorter and broader; leaf cells mostly unipapillose, occasionally with 2 papillae   (10)
+ Leaf apices longer and narrower; leaf cells mostly multipapillose, rarely with 1-2 papillae   (11)
10 (9) Stems without central strand; leaf margins entire to subentire; leaf cells rounded-oblong to elliptical, almost smooth or papillose with a single, large papilla   3 Didymodon asperifolius
+ Stems with central strand; leaf margins regularly toothed in the distal 1/2 -2/3; leaf cells rounded quadrate to transversely elliptical, with 1-2 papillae   6 Didymodon eroso-denticulatus
11 (9) Plants dark green to reddish brown, rather robust, to 8 cm high; leaves strongly squarrose; dorsal surface of costa roughened   8 Didymodon ferrugineus
+ Plants yellowish green, usually less than 4 cm high; leaves slightly squarrose; dorsal surface of costa smooth   (12)
12 (11) Leaves triangular-lanceolate; upper leaf margins bistratose   14 Didymodon rigidulus
+ Leaves broadly ovate-lanceolate; upper leaf margins unistratose   (13)
13 (12) Basal leaf cells not clearly differentiated, short-rectangular; peristome teeth elongate, twisted counterclockwise three times   7 Didymodon fallax
+ Basal leaf cells distinctly differentiated, narrowly rectangular; if present, peristome teeth short, twisted counterclockwise once   (14)
14 (13) Plants 5-8 mm high, in dense tufts; leaves narrowly ovate at the base, not plicate   12 Didymodon pallido-basis
+ Plants 10-20 mm high, in loose tufts; leaves broadly ovate at the base, plicate   19 Didymodon vinealis
15 (7) Leaf apices cyneous, apically swollen as a propagulum; leaf cells smooth   2 Didymodon anserinocapitatus
+ Leaf apices erect or not particularly bent, not swollen; at least upper leaf cells papillose   (16)
16 (15) Leaves broadly acute at the apex; leaf margins indistinct revolute   17 Didymodon tectorum
+ Leaves linear at the apex; leaf margins distinctly revolute   (17)
17 (16) Leaves triangular or deltoid at the base; margins distinctly revolute throughout; leaf cells usually quadrate to hexagonal, regularly arranged, cell walls thinner   (18)
+ Leaves broadly ovate-lanceolate to narrowly ovate-lanceolate; margins revolute usually only in the upper part; leaf cells triangular to pentagonal, irregularly arranged, cell walls thicker   (19)
18 (17) Plants 5-10 mm high; leaf cells with 2-4 blunt papillae; peristome teeth erect, usually fragile; opercula obliquely conic-rostrate   1 Didymodon acutus
+ Plants up to 35 mm high; leaf cells with single papilla; peristome teeth twisted, persistent; opercula erect, shortly rostrate   5 Didymodon ditrichoides
19 (17) Costa percurrent; leaf apices straight; leaf bases narrower, lower half of the margins not revolute   4a var. constrictus
+ Costa long excurrent, usually awns longer than leaf length; leaf apices flexed; leaf bases broader, lower half of the margins often revolute   4b var. flexicuspis

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