1a. Sterile leaves monomorphic, spirally arranged, linear or linear-lanceolate, with long white apical seta.
2a. Leaves thickly leathery, obtuse at apex ...................................................................................... 1. S. sibirica
2b. Leaves thinly leathery, acuminate at apex.
3a. Apical seta ca. 1/3 as long as leaves ..................................................................................... 2. S. vardei
3b. Apical seta ca. 1/5 as long as leaves ....................................................................................... 3. S. indica
1b. Sterile leaves dimorphic, arranged in 4 ranks, 2 dorsal and 2 ventral leaves, rarely nearly monomorphic, without long white apical seta.
4a. Stems and branches cylindrical, often reddish; sterile leaves nearly monomorphic, adpressed to stems and branches.
5a. Leaves not white-margined ......................................................................................... 4. S. sanguinolenta
5b. Leaves distinctly white-margined ................................................................................. 5. S. albocincta
4b. Branches often compressed; leaves dimorphic, dorsal leaves ascending, ventral leaves spreading.
6a. Strobili lax, not distinct from sterile stems; sporophylls monomorphic or dimorphic, almost conform with sterile leaves at same rank (non-resupinate) (see also 42b).
7a. Strobili cylindrical; sporophylls monomorphic, smaller than ventral leaves .......................... 6. S. helvetica
7b. Strobili rather loosely dorsiventrally compressed; sporophylls dimorphic, nearly conform with sterile leaves at same rank.
8a. Leaves denticulate at margin ............................................................................................ 7. S. nipponica
8b. Leaves shortly ciliolate at margin ......................................................................... 8. S. pseudonipponica
6b. Strobili compact, distinct from sterile stems; sporophylls in 4 ranks, monomorphic or dimorphic (dorsal sporophylls larger than ventral ones, rarely smaller).
9a. Strobili tetragonal; sporophylls nearly monomorphic.
10a. Stems forming rosettes, curling inward when dry.
11a. Dorsal and ventral leaves denticulate at margin .......................................... 9. S. tamariscina
11b. Dorsal leaves reflexed at margin; acroscopic margin of ventral leaves brown, membranous, lacerate ................................................................ 10. S. pulvinata
10b. Stems not forming rosettes, not curling inward when dry.
12a. Main stems creeping or prostrate in basal portion to scandent; rhizophores borne throughout stems.
13a. Main stems scandent, up to 1–2 m or longer.
14a. Axillary and ventral leaves with large basal auricles; dorsal leaves slightly white-margined; sporophylls ovate, acute or cuspidate; base of rhizophores without spines ................... 11. S. willdenowii
14b. Axillary and ventral leaves with small basal auricles; dorsal leaves white-margined; sporophylls ovate-lanceolate, acuminate; base of rhizophores with a few spines .................................. 12. S. helferi
13b. Main stems creeping, decumbent, or scandent, usually less than 1 m.
15a. Plants xerophytic, curling when dry; leaves ciliolate at margin.
16a. Dorsal leaves slightly smaller than and overlapping ventral leaves; leaves slightly lacerate and densely long ciliolate at margin ....................................... 13. S. nummularifolia
16b. Dorsal leaves much smaller than and not largely overlapping ventral leaves.
17a. Stems and branches scarlet; ventral leaves reflexed; margin of leaves sparsely toothed and long ciliolate at acroscopic base, entire elsewhere .................................. 14. S. rossii
17b. Stems and branches stramineous; ventral leaves not reflexed; margin of leaves shortly ciliolate throughout ..................................................... 15. S. sinensis
15b. Plants not xerophytic, not curling when dry; leaves entire or denticulate at margin.
18a. Leaves entire.
19a. Dorsal leaves auriculate at basiscopic base ...................................................................... 16. S. limbata
19b. Dorsal leaves not auriculate.
20a. Sporophylls not carinate on abaxial surface ........................................................... 17. S. uncinata
20b. Sporophylls carinate on abaxial surface .............................................................. 18. S. hainanensis
18b. Leaves denticulate or ciliolate at margin.
21a. Stems not articulate; rhizophores borne on ventral side in axils of branches.
22a. Leaves not white-margined, leaves on main stems and lateral branches ciliolate at margin, those on ultimate branches often subentire .............................. 19. S. siamensis
22b. Leaves white-margined, denticulate or shortly ciliolate ............................................... 20. S. davidii
21b. Stems slightly articulate beneath branching; rhizophores borne on dorsal side in axils of branches.
23a. Stems with a single vascular bundle ................................................................... 21. S. remotifolia
23b. Stems with 3 vascular bundles ......................................................................... 22. S. kraussiana
12b. Main stems erect, suberect, or ascending with short prostrate basal portion; rhizophores usually borne on basal to middle portions of main stem.
24a. Rhizophores borne on basal and middle portions of main stem or sometimes also on upper portion; leaves on main stem dimorphic.
25a. Plants erect; lateral branches regularly pinnately branched, twice forked, or simple; leaves entire or minutely denticulate at apex.
26a. Main stems 3–5 mm in diam., apical part black when dry; stomata invisible on dorsal leaves .............. 23. S. picta
26b. Main stems 2–3 mm in diam., apical part not black when dry; stomata on adaxial surface of dorsal leaves visible.
27a. Lateral branchlets simple or forked, or basal branchlets often forked; dorsal leaves overlapping distally ................................................................................. 24. S. delicatula
27b. Lateral branchlets simple, sometimes with irregular longer branches; dorsal leaves parallel, not overlapping distally ............................................................... 25. S. wallichii
25b. Plants erect, suberect, or ascending with prostrate rhizome; lateral branches many times pinnately branched; leaves denticulate.
28a. Leaves subleathery, shiny when dry; dorsal leaves aristate, arista ca. 1/2 as long as leaves or longer ......................................................................................... 26. S. commutata
28b. Leaves herbaceous, not shiny when dry; dorsal leaves acuminate to aristate, arista very short.
29a. Ventral leaves 4.5–7 mm ..................................................................... 27. S. rolandi-principis
29b. Ventral leaves less than 4.5 mm.
30a. Ventral leaves ovate-triangular or ovate-lanceolate; dorsal leaves aristate; surface of dorsal and ventral leaves scabrous ................ 28. S. scabrifolia
30b. Ventral leaves ovate-oblong or oblong-falcate; dorsal leaves acuminate or very shortly aristate; surface of leaves glabrous or that of ventral leaves scabrous.
31a. Dorsal and ventral leaves glabrous ................................................................. 29. S. doederleinii
31b. Ventral leaves scabrous ........................................................................................ 30. S. trachyphylla
24b. Rhizophores restricted to basal or lower portion of main stem or to prostrate rhizome; leaves on main stem monomorphic.
32a. Stems and branches pubescent.
33a. Main stems isotomously branched ............................................................................. 31. S. pubescens
33b. Main stems pinnately branched.
34a. Plants 45–100 cm high or more; axillary leaves biauriculate at base, ventral leaves auriculate at acroscopic base.
35a. Leaf portion of main stems and branches pubescent on both sides; main stems zigzag; leaves white-margined ............................................................. 32. S. trichoclada
35b. Leaf portion of main stems glabrous, ventral side of branches pubescent; main stems not zigzag; leaves not white-margined ................................... 33. S. pseudopaleifera
34b. Plants 10–45 cm high; axillary leaves not auriculate at base.
36a. Leaves thick, shrunken when dry; leaves on main stems peltate .................. 34. S. braunii
36b. Leaves thin, not shrunken; leaves on main stems basifixed ................................. 35. S. biformis
32b. Stems and branches glabrous.
37a. Plants usually more than 50 cm high, main stems robust, up to 4–5 mm in diam.; branches including leaves 5–10 m......................................................... 36. S. superba
37b. Plants usually less than 50 cm high, main stems 1–2 mm in diam., not so robust; branches including leaves less than 5 mm wide.
38a. Leaves on main stems approximate.
39a. Main stems reddish ....................................................................................... 37. S. stauntoniana
39b. Main stems stramineous ................................................................................. 38. S. involvens
38b. Leaves on main stems distant.
40a. Leaves on main stems peltate at base, not white-margined, ciliolate, very shrunken when dry .... 39. S. mairei
40b. Leaves on main stems basifixed, white-margined, denticulate, not shrunken when dry ...... 40. S. moellendorffii
9b. Strobili dorsiventrally complanate; dorsal and ventral sporophylls dimorphic.
41a. Strobili non-resupinate, i.e., dorsal sporophylls smaller than ventral ones.
42a. Strobili rather lax, often forked (see also 6a).
43a. Fertile branches short, pinnately branched; leaves up to 3.2 × 1.8 mm, margin denticulate, shortly ciliolate at base ....................................................................................................... 41. S. pallidissima
43b. Fertile branches erect or ascending, forked; leaves up to 2.3 × 1.2 mm, shortly ciliolate at margin, ciliolate at base ................................................................................... 42. S. laxistrobila
42b. Strobili shortly compact, solitary (or sometimes forked in S. prostrata).
44a. Leaves denticulate at margin ............................................................................. 43. S. tama-montana
44b. Leaves long ciliolate at margin.
45a. Strobili less than 4 mm; sporophylls plane .................................................................... 44. S. prostrata
45b. Strobili usually over 8 mm, up to 25 mm; larger ventral sporophylls navicular .............. 45. S. longistrobilina
41b. Strobili resupinate, i.e., dorsal sporophylls larger than ventral ones.
46a. Main stems erect or suberect; rhizophores restricted to basal or lower portion of main stems.
47a. Plants more than 30 cm high.
48a. Plants erect, 40–75 cm high; rhizophores restricted to basal portion of main stems .......... 46. S. decipiens
48b. Plants suberect, 30–40 cm high; rhizophores present in lower part of main stems ...... 47. S. bodinieri
47b. Plants usually less than 30 cm high.
49a. Sporophylls strongly dimorphic, ventral sporophylls up to 1/2 as long as dorsal ones.
50a. Plants up to 30 cm high; main stems robust; dorsal leaves obovate-aristate .............. 48. S. pennata
50b. Plants 5–15(–25) cm high; main stems thin.
51a. Ventral leaves up to 3 mm; sporophylls minutely denticulate ........................ 49. S. leptophylla
51b. Ventral leaves up to 3 mm; sporophylls sparsely ciliate ................................... 50. S. minutifolia
49b. Sporophylls not strongly dimorphic, ventral sporophylls ca. 2/3 as long as dorsal ones.
52a. Main stems tuberous at base .............................................................................. 51. S. chrysocaulos
52b. Main stems not tuberous at base.
53a. Axillary leaves ovate-deltoid ................................................................................. 52. S. effusa
53b. Axillary leaves ovate-lanceolate.
54a. Plants erect, main stems simple, branched in upper portion; leaves on stems and branches rather distant; rhizophores restricted to basal portion of main stems; base of ventral leaves shortly ciliolate .................. 53. S. labordei
54b. Plants ascending to erect, main stems branched in lower and upper portions; leaves on main stems rather approximate; rhizophores on lower portion of main stems; base of ventral leaves long ciliolate ............... 54. S. repanda
46b. Main stems prostrate or at least lower part prostrate, branches creeping or erect; rhizophores at intermittent intervals.
55a. Stems long creeping, fertile branches not erect, plants up to 30 cm or more; rhizophores on main stems and branches at intermittent intervals.
56a. Dorsal leaves obovate, long ciliolate in upper portion ..................................................................... 55. S. bisulcata
56b. Dorsal leaves not as above.
57a. Ultimate branches including leaves 10–15 mm wide ................................................. 56. S. megaphylla
57b. Ultimate branches including leaves less than 8 mm wide.
58a. Dorsal leaves long aristate; sporophyll-pteryx of dorsal sporophylls not reaching apex (incomplete).
59a. Basiscopic margin of ventral leaves entire .................................................................................. 57. S. ornata
59b. Basiscopic margin of ventral leaves ciliolate ..................................................................... 58. S. amblyphylla
58b. Dorsal leaves acuminate or shortly aristate; sporophyll-pteryx of dorsal sporophylls reaching apex or almost so (complete).
60a. Leaves glabrous ................................................................................................... 59. S. monospora
60b. Leaves scabrous .............................................................................................. 60. S. trichophylla
55b. Main stems and branches prostrate or fertile branches suberect, plants usually less than 20 cm, or main stems erect, normally less than 25 cm high; rhizophores on prostrate stems or restricted to basal portion of erect main stems.
61a. Prostrate stems very short, thin; plants small; fertile stems prominent.
62a. Sporangia only on ventral side of strobilus; sporophylls denticulate ................................................ 61. S. devolii
62b. Sporangia on both sides of strobilus; sporophylls long ciliolate ....................................................... 62. S. ciliaris
61b. Plants not as above.
63a. Acroscopic base of ventral leaves not long ciliolate; leaves denticulate or shortly ciliolate at margin.
64a. Dorsal leaves rounded or obtuse at apex; leaves denticulate at margin .............................. 63. S. kouytcheensis
64b. Dorsal leaves acuminate or aristate; leaves denticulate or shortly ciliolate at margin.
65a. Fertile branches short, complanate with sterile main stems and branches, creeping or ascending.
66a. Leaves shortly ciliolate at margin ...................................................................................... 64. S. boninensis
66b. Leaves minutely denticulate at margin ......................................................................... 65. S. heterostachys
65b. Fertile branches long, erect.
67a. Dorsal leaves cordate at base, margin shortly ciliolate ......................................................... 53. S. labordei
67b. Dorsal leaves not cordate at base, margin minutely denticulate .................................. 65. S. heterostachys
63b. Acroscopic base of ventral leaves long ciliolate.
68a. Fertile branches erect; ventral leaves involute in dry conditions.
69a. Basiscopic base of ventral leaves with few long cilia .................................................................. 66. S. kurzii
69b. Basiscopic base of ventral leaves shortly ciliolate, elsewhere subentire.
70a. Sporophylls obviously dimorphic ....................................................................................... 67. S. xipholepis
70b. Sporophylls slightly dimorphic ............................................................................................. 68. S. vaginata
68b. Fertile branches creeping; ventral leaves not involute in dry conditions.
71a. Ventral leaves oblong-falcate; dorsal leaves ovate-lanceolate ........................................ 69. S. drepanophylla
71b. Ventral leaves not oblong-falcate; dorsal leaves ovate or suborbicular.
72a. Leaves not white-margined, sparsely ciliolate ................................................................. 70. S. chaetoloma
72b. Leaves distinctly white-margined.
73a. Ventral leaves denticulate at margin, bearing several long hairs at basal portion ........ 71. S. lutchuensis
73b. Ventral leaves long ciliolate at margin ........................................................................... 72. S. albociliata