1. Costa in transverse section lacking guide cells, with a median layer of connected or disconnected small green cells or stereid cells.................................................................................................................................... 2
1. Costa in transverse section nearly always with large guide cells, without a median layer of green cells or stereid cells............................................................................................................................................................. 4
2. Alar cells clearly inflated; costal green cells in a median band, enclosed dorsally and ventrally by larger, thick-walled, hyaline cells or sometimes interspersed among the dorsal hyaline cells; annuli not developed.............................................................................................................................................................
........................................................................................................................................... 27. Paraleucobryum
2. Alar cells not much differentiated; costal green cells in a group of disconnected median stereids, enclosed dorsally and ventrally by large, thin-walled, hyaline cells; annuli well developed...................... 3
3. Costa generally narrower, less than 1/3 the leaf base width, with a few ventral stereids in the middle of costa; peristome teeth divided; plants usually green or yellowish brown when dry; brood bodies absent; leaf apex serrulate.................................................................................................................................. 8. Campylopodiella
3. Costa generally broader, more than ½ the leaf base width, without ventral stereids in the middle of costa; peristome teeth undivided; plants usually grayish green when dry; brood bodies common; leaf apex smooth
................................................................................................................................................................ 6. Brothera
4. Neck of capsules well developed, broad or very long..................................................................................... 5
4. Neck of capsules none, rarely very short and narrower.................................................................................. 7
5. Neck of capsules very long and narrow, at least as long as the urn............................................ 31. Trematodon
5. Neck of capsules short and generally broad, rarely as much as ½ the total length of the urn.......................... 6
6. Opercula and peristome teeth none; setae very short; leaves sheathing at base, gradually narrowed to a
short or long subula............................................................................................................................ 7. Bruchia
6. Opercula and peristome teeth well developed; setae elongate; leaves not sheathing at base, gradually
acuminate with obtuse apices.................................................................................................... 32. Wilsoniella
7. Alar cells not or not noticeably differentiated...................................................................................................... 8
7. Alar cells clearly differentiated in a group, usually inflated.............................................................................. 22
8. Upper laminal cells mammillose or papillose................................................................................................. 9
8. All laminal cells smooth.................................................................................................................................. 12
9. Peristome teeth absent; capsules 8-ribbed when dry; laminal cells pluripapillose...................... 1. Amphidium
9. Peristome teeth well developed; capsules smooth or furrowed when dry; laminal cells mammillose or conically
to coarsely papillose............................................................................................................................................ 10
10. Capsules furrowed when dry; leaves narrowly lanceolate, mostly acute at the apex, keeled; laminal cells often coarsely papillose..................................................................................................... 11. Cynodontium
10. Capsules smooth when dry; leaves broadly lanceolate or oblong-ligulate, broadly acute to rounded at the
apex, subtubulose; laminal cells mammillose or conically papillose........................................................ 11
11. Peristome teeth forked, papillose........................................................................................... 12. Dichodontium
11. Peristome teeth not forked, smooth............................................................................................ 25. Oreoweisia
12. Peristome teeth absent; stems julaceous; leaves broad, oval to oblong-ovate, rounded-obtuse or broadly acute at the apex............................................................................................................................. 13
12. Peristome teeth present; stems not julaceous; leaves narrow, lanceolate, gradually narrowed to a sharp acute apex or abruptly narrowed from a strongly sheathing base to a subulate apex............................. 14
13. Dioicous; leaves oval, broadly acute, sharply bent to one side at the tips; costa percurrent; apical laminal cells irregular hexagonal or rhombic....................................................................................... 2. Aongstroemia
13. Autoicous; leaves oblong-ovate, rounded-obtuse, straight at the apex; costa excurrent; apical laminal cells oblong-rectangular to rhomboidal..................................................................................... 3. Aongstroemiopsis
14. Capsules deeply 8-ribbed when dry; leaves oblong-lanceolate, slightly narrowed upward, sharply acute at the apex......................................................................................................................... 29. Rhabdoweisia
14. Capsules smooth or irregularly furrowed when dry, not ribbed; leaves narrowly to linear-lanceolate, abruptly narrowed from a strongly sheathing or nonsheathing base, subulate at the apex.................... 15
15. Setae curved or cygneous when moist............................................................................................................... 16
15. Setae straight or sometimes flexuose when moist........................................................................................... 18
16. Autoicous; peristome teeth entire or slightly perforate, vertically striate throughout; leaf margins bistratose
.......................................................................................................................................................... 24. Oreas
16. Dioicous; peristome teeth divided to the middle, vertically striate only at the base; leaf margins unistratose
...................................................................................................................................................................... 17
17. Capsules with stomata in the neck; spores finely papillose................................................ 9. Campylopodium
17. Capsules without stomata in the neck; spores warty....................................................... 21. Microcampylopus
18. Leaves strongly crispate when dry; upper laminal cells short, subquadrate to short-rectangular......... 19
18. Leaves not crispate or contorted when dry; upper laminal cells elongate, narrowly to oblong-rectangular........................................................................................................................................................
...................................................................................................................................................................... 20
19. Capsules curved, distinctly strumose ........................................................................................ 23. Oncophorus
19. Capsules erect, not strumose................................................................................................... 30. Symblepharis
20. Autoicous; calyptrae very large, longer than capsules; peristome teeth divided to the base.....................
.......................................................................................................................................... 5. Atractylocarpus
20. Dioicous; calyptrae shorter than capsules; peristome teeth irregularly divided only to the middle.... 21
21. Capsules globose, erect, symmetric; peristome teeth short, simple or irregularly split only at the tips........
............................................................................................................22. Microdus
21. Capsules subglobose to oblong-cylindric, asymmetric; peristome teeth elongated, clearly divided about halfway down or to the base.......................................................................................................... 13. Dicranella
22. Costa very broad, more than 1/3 the leaf base width.................................................................................. 23
22. Costa narrow, less than 1/3 the leaf base width.......................................................................................... 24
23. Capsules usually deeply furrowed when dry; annuli compound; calyptrae often fringed at the base; peristome teeth divided only to the middle; leaves not conspicuously setaceous................ 10. Campylopus
23. Capsules smooth when dry; annuli none; calyptrae often entire at the base; peristome teeth divided nearly to the base; leaves conspicuously long-setaceous............................................................ 14. Dicranodontium
24. Margins distinctly bordered by linear cells, usually hyaline near the leaf base; inner laminal cells differentiated............................................................................................................................................... 25
24. Margins not clearly bordered; inner laminal cells usually not differentiated from marginal cells...... 26
25. Laminal cells coarsely compound-papillose............................................................................... 20. Leucoloma
25. Laminal cells smooth................................................................................................................. 15. Dicranoloma
26. Upper laminal cells rounded or isodiametric, strongly incrassate; perichaetial leaves with markedly elongated, convolute sheaths enfolding the setae and extending 1/3 – 2/3 the seta length.................... 18. Holomitrium
26. Upper laminal cells rectangular or elongate, moderately thick-walled; perichaetial leaves with short sheaths enfolding the setae only at the base............................................................................................. 27
27. Leaves crispate when dry.................................................................................................................................... 28
27. Leaves falcate-secund, not crispate when dry................................................................................................... 29
28. Peristome teeth undivided or only slightly divided at the tips, without vertical striate, smooth or papillose throughout........................................................................................................ 16. Dicranoweisia
28. Peristome teeth divided in the upper half or lower, with vertical striate nearly throughout......................
......................................................................................................................................... 26. Orthodicranum
29. Autoicous; costa in cross section lacking stereid band or with only a few poorly developed stereids; peristome teeth undivided or variously divided to the middle or less........................................................... 30
29. Dioicous; costa in cross section with 2 stereid bands; peristome teeth divided in the upper ½ –2/3, sometimes the teeth poorly developed or lacking........................................................................................... 31
30. Setae 3–6 mm long, stout; capsules erect, obovoid, nearly symmetric, contracted below the mouth, tapered to the base when dry; peristome teeth irregularly divided in the upper half or less..... 4. Arctoa
30. Setae 7–16 mm long, slender; capsules suberect to inclined, oblong-cylindric, curved, sometimes strumose, not contracted below the mouth or tapered to the base when dry; peristome teeth clearly bifid halfway down....................................................................................................................... 19. Kiaeria
31. Peristome teeth absent; capsules erect; plants often yellowish green................. 28. Pseudochorisodontium
31. Peristome teeth well developed; capsules curved, suberect, horizontal or inclined; plants often bright green or brownish green................................................................................................................. 17. Dicranum