l. Protonemata persistent; leaves small and appressed on stems, without lamellae.....................................2
l. Protonemata not persistent; leaves large and clasping stems with a sheathing base; lamellae numerous........ 3
2. Costa stout, setulosely aristate, coarsely spinose above..........................................16. P. spinulosum
2. Costa slender, disappearing at leaf apex, smooth.....................................................2. P. camusii
3. Lamellae present only on ventral surface or lateral sides of the costa.................................................4
3. Lamellae densely covering the upper part of leaves except at margins................................................5
4. Plants rather robust, up to 8 cm high; leaf apices broad; margins grossly toothed; lamellae only on the ventral surface of the costa.................................................................................................. 15. P. proliferum
4. Plants slender, only 2 cm high; leaf apices narrow; margins serrulate; lamellae on ventral surface and lateral sides of the costa................................................................................................... 12. P. nudiusculum
5. Apical cells of lamellae double, flask-like.................................................................9. P. microstomum
5. Apical cells of lamellae single or sometimes double, but not flask-like....................................................6
6. Plants usually only 5 mm high; apical cells of lamellae 1–2................................................10. P. minus
6. Plants usually more than 2 cm high; apical cells of lamellae mostly single, rarely 2...............................7
7. Leaf margins mostly bistratose, occasionally unistratose....................................................................8
7. Leaf margins always unistratose.....................................................................................................12
8. Lamellae mostly 4–5 cells high, apical cells usually double, smaller than other cells of lamellae.......... 9
8. Lamellae mostly (1–)2–4 cells high, apical cells single, similar to other cells of lamellae................... 10
9. Plants usually 8 cm high or higher; leaves lanceolate..........................................13. P. pergranulatum
9. Plants less than 8 cm high; leaves narrowly lanceolate.........................................8. P. japonicum
10. Sheath-margins remotely dentate, wide, mostly unistratose except at outermost margins; lamellae more or less crenate as seen in side view, mostly 2–3(–4) cells high................................ 4. P. contortum
10. Sheath-margins serrate, narrower, mostly bistratose; lamellae mostly straight as seen in side view, usually 1–2 cells, sometimes up to 4 cells high......................................................................................... 11
11. Plants larger, up to 8.0(–10) cm high; leaves up to 1.0 cm long; lamellae 1–2 cells high with apical cells partially in pairs; leaf margins typically bistratose........................................... 3a. P. cirratum subsp. cirratum
11. Plants smaller, only up to 3.0 cm high; leaves less than 0.5 cm long; lamellae sometimes up to 4 cells high with apical cells not in pairs; leaf margins typically unistratose.................... 3b. P. cirratum subsp. fuscatum
12. Margins of the sheathing base ciliate.....................................................6. P. fastigiatum
12. Margins of the sheathing bases entire......................................................................................13
13. Apical cells of lamellae usually yellowish brown, distinctly thick-walled.........................................14
13. Apical cells of lamellae not yellowish brown, not distinctly or rarely thick-walled above.......................... 16
14. Apical cells of lamellae oblong-oval....................................................................18. P. urnigerum
14. Apical cells of lamellae transversally rectangular.................................................................................15
15. Costa aristate; apical cells of lamellae smooth.....................................................14. P. perichaetiale
15. Costa not aristate; apical cells of lamellae densely papillose.................................5. P. dentatum
16. Leaf lamellae on the ventral surface disappearing at 5–7 rows of marginal cells; lamellae 3–4 cells high
...............................................................................................................17. P. subfuscatum
16. Leaf lamellae densely covering nearly entire ventral surface, lamellae 3–6 cells high......................... 17
17. Leaves strongly crisped when dry; the width of apical cells of lamellae larger than length, emarginate above in cross section..............................................................................................7. P. inflexum
17. Leaves usually incurved when dry; the length of apical cells of lamellae larger than width, not emarginate above in cross section......................................................................................................................18
18. Apical cells of lamellae in cross section mostly elliptic, sometimes finely papillose..........11. P. neesii
18. Apical cells of lamellae in cross section rounded or rounded-oval, smooth......................1. P. aloides