1. Costa slender, ending at or below the leaf apex; leaf cells smooth or unipapillose......................................... 2
1. Costa stout, percurrent or excurent; leaf cells multi-papillose or sometimes unipapillose............................ 3
2. Leaves triangular-lanceolate; costa ending well below the apex; leaf cells smooth; capsules ovoid...........
................................................................................................................................................... 16. D. rufidulus
2. Leaves ovate-lanceolate; costa ending at the apex; leaf cells usually unipapillose; capsules cylindrical....
........................................................................................................................................................... 15. D. rivicola
3. Leaves short and broad, usually broadly ovate to oblong-ovate or ligulate, blunt or rounded at the apex....... 4
3. Leaves narrowly ovate, triangular or linear-lanceolate, gradually acute or acuminate..................................... 7
4. Plants only ca. 0.5 cm high; leaves imbricate, broadly ovate at the base
......................... 13. D. perobtusus
4. Plants (1.0–)2.5–6.0 cm high; leaves spreading, narrowly oblong-ovate at the base.................................. 5
5. Plants bright green; leaf apex broad and rounded, slightly cucullate
........................................ 18. D. tophaceus
5. Plants reddish brown; leaf apex narrowly and acuminate, not cucullate............................................................. 6
6. Cells of the abaxial surface of costa linear-oblong, walls slightly sinuate; upper leaf cells smooth, or occasionally with 1 indistinct low papilla
............................................................................ 10. D. japonicus
6. Cells of the abaxial surface of costa quadrate to short-rectangular, walls not sinuate; upper leaf cells usually with 1 blunt papilla
................................................................................................... 11. D. nigrescens
7. Leaves squarrose when moist; leaf cell walls strongly and irregularly thickened............................................. 8
7. Leaves erect-spreading when moist; leaf cell walls not particularly thickened.............................................. 15
8. Leaf bases very broad, deltoid, narrowly lanceolate toward the apex; basal cells linear, very thick-walled, sinuose because of porose walls
................................................................................ 9. D. giganteus
8. Leaf bases ovate-lanceolate; basal cells shortly rectangular, slightly thick-walled, not porose................ 9
9. Leaf apices shorter and broader; leaf cells mostly unipapillose, occasionally with 2 papillae..................... 10
9. Leaf apices longer and narrower; leaf cells mostly multipapillose, rarely with 1–2 papillae....................... 11
10. 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. D. asperifolius
10. 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. D. eroso-denticulatus
11. Plants dark green to reddish brown, rather robust, to 8 cm high; leaves strongly squarrose; dorsal surface of costa roughened
.................................................................................................................... 8. D. ferrugineus
11. Plants yellowish green, usually less than 4 cm high; leaves slightly squarrose; dorsal surface of costa smooth.............12
12. Leaves triangular-lanceolate; upper leaf margins bistratose
.............................................. 14. D. rigidulus
12. Leaves broadly ovate-lanceolate; upper leaf margins unistratose........................................................... 13
13. Basal leaf cells not clearly differentiated, short-rectangular; peristome teeth elongate, twisted counterclockwise three times
........................................................................................................... 7. D. fallax
13. Basal leaf cells distinctly differentiated, narrowly rectangular; if present, peristome teeth short, twisted counterclockwise once...................................................................................................................................... 14
14. Plants 5–8 mm high, in dense tufts; leaves narrowly ovate at the base, not plicate
........12. D. pallidobasis
14. Plants 10–20 mm high, in loose tufts; leaves broadly ovate at the base, plicate
.............. 19. D. vinealis
15. Leaf apices cyneous, apically swollen as a propagulum; leaf cells smooth
............. 2. D. anserinocapitatus
15. Leaf apices erect or not particularly bent, not swollen; at least upper leaf cells papillose......................... 16
16. Leaves broadly acute at the apex; leaf margins indistinct revolute
.................................. 17. D. tectorum
16. Leaves linear at the apex; leaf margins distinctly revolute...................................................................... 17
17. Leaves triangular or deltoid at the base; margins distinctly revolute throughout; leaf cells usually quadrate to hexagonal, regularly arranged, cell walls thinner........................................................................................ 18
17. 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. Plants 5–10 mm high; leaf cells with 2–4 blunt papillae; peristome teeth erect, usually fragile; opercula obliquely conic-rostrate
............................................................................................. 1. D. acutus
18. Plants up to 35 mm high; leaf cells with single papilla; peristome teeth twisted, persistent; opercula erect, shortly rostrate
....................................................................................................... 5. D. ditrichoides
19. Costa percurrent; leaf apices straight; leaf bases narrower, lower half of the margins not revolute...............
19. Costa long excurrent, usually awns longer than leaf length; leaf apices flexed; leaf bases broader, lower half of the margins often revolute
.................................................................. 4b. D. constrictus var. flexicupis