Key to species of Leptochilus
1. Laminae simple or sometime lamina base lobed...............................................................................................................................2.
- Laminae lobed, pinnatifid, or rarely 2-pinnate to 4-pinnatifid........................................................................................................32.
2. Sori orbicular or elongated, irregularly scattered ..............................................................................................................................3.
- Sori linear, acrostichoid, or elongated then regularly in one row along each side of midrib............................................................4.
3. Petioles and rachises sparely scaly or nearly glabrous, laminae 6–9 × 1.3–1.9 cm ........................................... L. khammouanensis
- Petioles and rachises distinctively scaly, laminae (3.5)8–30 × (0.2) 1.5–5.5 cm ............................................................... L. pteropus
4. Fronds distinctly dimorphic...............................................................................................................................................................5.
- Frond monomorphic or slightly dimorphic .....................................................................................................................................25.
5. Fronds strongly dimorphic, fertile fronds linear, sori fully cover the lower surface.........................................................................6.
- Fronds dimorphic, fertile fronds lanceolate, broadly lanceolate, or ovate, sori shortly linear or long linear .................................17.
6. Sori acrostichoid................................................................................................................................................................................7.
- Sori shortly linear ............................................................................................................................................................................16.
7. Sterile fronds shortly petiolated or sessile.........................................................................................................................................8.
- Sterile fronds distinctly petiolated...................................................................................................................................................13.
8. Sterile fronds less than 10 cm long....................................................................................................................................................9.
- Sterile fronds more than 10 cm long ...............................................................................................................................................11.
9. Apexes of sterile laminae cuneate .................................................................................................................................. L. metallicus
- Apexes of sterile laminae rounded ..................................................................................................................................................10.
10. Length of sterile laminae 3-6 times than lamina width ......................................................................................................... L. minor
- Length of sterile laminae 2-3 times than lamina width .................................................................................................. L. ovatifolius
11. Sterile laminae ca. 0.5 cm wide.............................................................................................................................................. L. wallii
- Sterile laminae more than 1 cm wide ..............................................................................................................................................12.
12. Rhizome sparely scaly with few roots................................................................................................................................ L. axillaris
- Rhizome scaly with many roots ......................................................................................................................................... L. brevipes
13. Laminae lobed .................................................................................................................................................................... L. poilanei
- Laminae entire.................................................................................................................................................................................14.
14. Sterile fronds less than 10 cm long.............................................................................................................................. L. cantoniensis
- Sterile fronds more than 10 cm long ...............................................................................................................................................15. 15. Sterile laminae elliptic or narrowly ovate ....................................................................................................................... L. decurrens
- Sterile laminae lanceolate............................................................................................................................................. L. kachinensis
16. Fertile fronds longer than sterile frond.............................................................................................................................. L. evrardii
- Fertile fronds the same length as, or shorter than sterile frond .............................................................................. L. mengsongensis
17. Fertile fronds shorter than, the same length as, or slight longer than sterile fronds........................................................................18.
- Fertile fronds at least 1.5 times longer than sterile fronds ..............................................................................................................20.
18. Fertile fronds shorter than sterile frond ...................................................................................................................... L. vietnamensis
- Fertile fronds the same length as or slightly longer than sterile frond ............................................................................................19.
19. Laminae thickly chartaceous, petioles of sterile fronds (0.5) 2–5 cm long........................................................................... L. chingii
- Laminae thinly chartaceous, petioles of sterile fronds (0.6)– 1.7 cm long ....................................................... L. luangprabangensis
20. Fertile fronds 1.5 – 2 times longer than sterile fronds.......................................................................................................................21.
- Fertile fronds more than two times longer than sterile fronds.........................................................................................................22.
21. Fertile laminae oblong to broadly oblong ................................................................................................................. L. pedunculatus
- Fertile laminae ovate to narrowly ovate ................................................................................................................................ L. ovatus
22. Fertile laminae narrowly lanceolate .......................................................................................................................... L. sarawakensis
- Fertile laminae broadly lanceolate to ovate.....................................................................................................................................23.
23. Sterile laminae elliptic-lanceolate, base gradually narrowed....................................................................................... L. daklakensis
- Sterile laminae ovate-lanceolate to ovate, base truncate .................................................................................................................24.
24. Fertile laminae 1.5–1.7 cm wide, venation indistinct............................................................................................................... L. locii
- Fertile laminae 3–7 cm wide, venation prominent .................................................................................................................... L. wui
25. Sori interrupted................................................................................................................................................................................26.
- Sori continuous................................................................................................................................................................................27.
26. Circumvascular sheaths present in rhizome, interrupted sori mostly oblong, irregular in shape............................. L. hemionitideus
- Circumvascular sheaths absent in rhizome, interrupted sori shortly linear to linear, regular in shape ..................... L. macrophyllus
27. Venation indistinct ................................................................................................................................................................. L. henryi
- Venation distinct ..............................................................................................................................................................................28.
28. Lamina base with outgrows or lobed...............................................................................................................................................29.
- Lamina base entire...........................................................................................................................................................................31.
29. Petioles distinctively winged......................................................................................................................................... L. hemitomus
- Petioles wingless or slightly winged ...............................................................................................................................................30.
30. Lamina base slightly lobed................................................................................................................................................. L. saxicola
- Laminae distinctly lobed, lobes irregular .................................................................................................................... L. shintenensis
31. Laminae widest at middle or above middle part ................................................................................................................. L. leveillei
- Laminae widest bellow middle part ................................................................................................................................... L. wrightii
32. Laminae 2-pinnate to 4-pinnatifid ............................................................................................................................. L. heterophyllus
- Laminae lobed, pinnatifid................................................................................................................................................................33.
33. Laminae lobed in different extent, from 2- or 3-forked, pedately lobed, to digitately lobed..........................................................34.
- Laminae pinnatifid...........................................................................................................................................................................35.
34. Laminae trilobed, lobe base not narrowed ................................................................................................................... L. ornithopus
- Laminae often digitately lobed, or if trilobed then lobe base distinctly narrowed............................................................ L. digitatus
35. Fronds large, 60–120 cm .................................................................................................................................................................36.
- Fronds less than 60 cm ....................................................................................................................................................................38.
36. Lobes often more than 6 pairs, occurs in mountains with acid soils................................................................................... L. elegans
- Lobes 2 – 6 pairs, occurs in limestone mountains.............................................................................................................................37.
37. Laminae thinly chartaceous.................................................................................................................................... L. sinovietnamica
- Laminae thickly chartaceous ........................................................................................................................................ L. wusugongii
38. Sori oblong, close to the lobe margins ............................................................................................................................. L. oblongus
- Sori linear, rarely oblong, located on main lateral veins between midribs and lobe margins .........................................................39.
39. Rachis broadly winged ....................................................................................................................................................................40.
- Rachis narrowly winged, partial rachis wingless ............................................................................................................................44.
40. Widest of lobes 2.5–4 cm .............................................................................................................................................. L. pothifolius
- Widest of lobes less than 2 cm ........................................................................................................................................................41.
41. Lobes 10 – 12 pairs.................................................................................................................................................... L. dissimilialatus
- Lobes 6 – 9 pairs.................................................................................................................................................................................42
42. Basal most pair of lobes forked................................................................................................................................. L. sanjiangensis
- Basal most pair of lobes not forked.................................................................................................................................................43.
43. Lamia margins flat or sometimes slightly undulate, lobes 12–15 × 1.9–2.4 cm ........................................................ L. neolongipes
- Lamina margins distinctly undulate-repand, lobes 5–12 × 0.9–1.6 cm ........................................................................... L. flexilobus
44. Fronds oblong, lobes 5–8(–14) pairs..............................................................................................................................................45.
- Fronds broad oblong to ovate-deltoid, lobes 1 – 4 pairs ...................................................................................................................46.
45. Sori oblong to shortly linear........................................................................................................................................... L. multilobus
- Sori linear ......................................................................................................................................................................... L. ellipticus
46. Fronds less than 18 cm long ............................................................................................................................................................47.
- Fronds more than 20 cm long..........................................................................................................................................................49.
47. Sori oblong .......................................................................................................................................................... L. bolikhamsaiensis
- Sori shortly linear ............................................................................................................................................................................48. 48. Lobes 1–2 pairs.................................................................................................................................................................... L. gracilis
- Lobes 4–6 pairs............................................................................................................................................................ L. chilangensis
49. Laminae chartaceous to thickly chartaceous ..................................................................................................................... L. longipes
- Laminae herbaceous to thinly chartaceous......................................................................................................................................50.
50. Petioles the same length or slightly longer than laminae ................................................................................................. L. scandens
- Petioles almost as two times as laminae..................................................................................................................... L. pentaphyllus