1. Costa in transverse section without clearly defined stereids............................................................................... 2
1. Costa in transverse section with clearly defined stereids.................................................................................... 5
2. Dorsal cells of the costa with very thick walls and small lumina (smaller than the ventral cells), thus qualifying as substereids; leaves usually falcate-secund................................................... 13. C. subfragilis
2. Dorsal cells of the costa with only incrassate walls and large lumina, becoming too large to be qualified as substereids; leaves usually erect................................................................................................................. 3
3. Costa broader, occupying 3/4 the leaf base width; lamina not beyond 1/3 the leaf length; alar cells distinctly protruding into the costa.................................................................................................................... 6. C. gracilis
3. Costa narrower, often less than 2/3 the leaf base width; lamina extending beyond 1/3 the leaf length; alar cells not or slightly protruding into the costa............................................................................................................... 4
4. Costa smooth at back above; upper leaf cells rectangular.................................................... 11. C. schimperi
4. Costa ridged at back above; upper leaf cells subquadrate to short-rectangular.................. 14. C. subulatus
5. Costa in transverse section with both dorsal and ventral stereid bands............................................................... 6
5. Costa in transverse section with only dorsal stereid band.................................................................................... 9
6. Basal leaf cells subquadrate to short-rectangular............................................................................................ 7
6. Basal leaf cells moderately long-rectangular.................................................................................................. 8
7. Leaves broadly lanceolate, contracted at base; costa narrower, occupying ca. 1/3 the leaf base width, with lamellae at back in the upper part, ending in a long, distinct hyaline, serrate hairpoint....... 16. C. umbellatus
7. Leaves narrowly lanceolate, not contracted at base; costa broader, occupying ca. 1/2 the leaf base width, smooth or rarely slightly ridged at back in the upper part, ending in a long concolorous tip........... 8. C. japonicus
8. Costa ending in a subhyaline to hyaline point, ridged at back in the upper part, in transverse section clearly with ventral stereid band; leaf base contracted; calyptrae fringed at base; capsules erect, symmetric and scabrous at base................................................................................................ 3. C. ericoides
8. Costa not ending in a hyaline point, smooth at back in the upper part, with ventral substereid band in transverse section; leaf base not contracted; calyptrae ciliate at base; capsule curved, strumose and smooth at base............................................................................................................................. 2. C. comosus
9. Basal leaf cells rather thin-walled........................................................................................................................ 10
9. Basal leaf cells thick-walled................................................................................................................................. 16
10. Costa ending in a long hyaline hairpoint...................................................................................................... 11
10. Costa not ending in a hyaline hairpoint or ending in a subhyaline point................................................... 12
11. Plants larger, to 8 cm high, in dense cushion, densely tomentose below; costal cells of abaxial surface quadrate to short-rectangular..................................................................................... 7. C. hemitrichius
11. Plants smaller, to 4 cm high, in loose tufts, scarcely tomentose below; costa cells of abaxial surface long-rectangular..................................................................................................................................... 12. C. schmidii
12. Sterile plants not comose foliate; leaves ending in a long, narrow, channeled tip........ 10. C. pyriformis
12. Sterile plants comose foliate; leaves not ending in a channeled tip........................................................ 13
13. Costa widest at base, gradually narrowed upward, ending in a subhyaline point; upper leaf cells rhomboidal to elongate; brood leaves lacking............................................................................................... 9. C. laxitexus
13. Costa widest about in the middle of leaves, gradually narrowed toward leaf base, ending in a concolorous point; upper leaf cells quadrate, oval or rectangular; brood leaves common in comal tufts........................ 14
14. Upper leaf cells rectangular.................................................. 17. C. zollingerianus
14. Upper leaf cells quadrate to short-rectangular or oval.........................................15
15. Upper leaf cells quadrate to short-rectangular......................................................... 5a. C. fragilis ssp. fragilis
16. Costa not ending in a hyaline hairpoint nor in a cucullate tip; upper leaf cells, quadrate to short-rectangular or slightly oblique ............................................................................................. 4. C. flexuosus
16. Costa ending in a hyaline hairpoint, sometimes in a cucullate tip; upper leaf cells rhomboidal or elongate-oval............................................................................17
17. Costa with lamellae at back in the upper part; upper leaf cells rhomboidal........................ 15. C. taiwanensis
17. Costa with ridges at back in the upper part; upper leaf cells elongate-oval........... 18