| 1 | Aquatic plants. |
| 1' | Land plants or epiphytes. |
| 2 | Plants floating. Leaves small, simple or bilobed |
| 2' | Plants rooted in earth or on rocks. Leaves larger, more divided. |
| 3 | Leaves 4-partite. Sporocarps attached to stipes |
| 3' | Leaves not 4-partite. Sporangia singly or in sori on lower surface of lamina. |
| 4 | Sporangia borne singly, protected by reflexed edges of narrow lamina. |
| 4' | Sporangia grouped in sori, on lower surface of lamina, not protected by reflexed edges. |
| 5 | Fern of stream-beds in deep shade. Fronds pinnatifid, sori without indusia |
| 5' | Fern of open swamps. Fronds bipinnatifid, sori indusiate |
| 6 | Epiphytes. |
| 6' | Terrestrial plants, or climbers starting from the ground, or rock-plants. |
| 7 | Fronds simple, not over 2 mm wide, with a single vein, or with a few simple lateral soriferous veins close to the main vein |
| 7' | Fronds branched, or if simple with a more complex venation. |
| 8 | Lamina one cell thick apart from midribs of segments |
| 8' | Lamina throughout more than one cell thick. |
| 9 | Sporangia embedded in slender cylindrical appendages attached to surface of frond. |
| 9' | Sporangia not so arranged. |
| 10 | Sori not indusiate (sometimes otherwise protected). |
| 10' | Sori indusiate. |
| 11 | Sporangia not acrostichoid. |
| 11' | Sporangia acrostichoid, covering entirely part or whole of a frond. |
| 12 | Sori superficial (not in pockets or grooves). |
| 12' | Sori in pockets or grooves (which are sometimes marginal). |
| 13 | Fronds simple, pinnatifid or pinnate; if pinnate, pinnae not articulate to rachis. |
| 13' | Fronds pinnate, pinnae articulate to rachis. |
| 14 | Veins much anastomosing |
| 14' | Veins not or slightly anastomosing. |
| 15 | Frond and stipe ± hairy; spores trilete |
| 15' | Frond and stipe not hairy; spores monolete |
| 16 | Pinnae entire |
| 16' | Pinnae lobed |
| 17 | Sori in pockets or depressions, +- circular. |
| 17' | Sori elongate, in grooves. |
| 18 | Veins anastomosing; or, if free, fronds not hairy |
| 18' | Veins free, fronds more or less hairy |
| 19 | Grooves all evenly oblique to costa |
| 19' | Grooves marginal or parallel to margin, or uneven in direction, sometimes anastomosing. |
| 20 | Scales entirely opaque, usually brown |
| 20' | Scales nearly black, strongly clathrate, lumina of cells translucent |
| 21 | Veins much anastomosing; spores without perispore |
| 21' | Veins free or slightly anastomosing near edge; perispore present. |
| 22 | Sori elongate along veins |
| 22' | Sori otherwise. |
| 23 | Sori elongate along edge of lamina. |
| 23' | Sori otherwise. |
| 24 | Pinnae articulate to rachis |
| 24' | Pinnae (if any) not articulate to rachis. |
| 25 | Rhizome protostelic |
| 25' | Rhizome with more complex vascular system |
| 26 | Fronds articulate to rhizome. |
| 26' | Fronds not articulate to rhizome |
| 27 | Sori at ends of veins, near edge of lamina. |
| 27' | Sori close to costa of the simple frond |
| 28 | Pinnae (if present) not jointed to rachis |
| 28' | Pinnae jointed to rachis |
| 29 | High-climbing rhizome starting from the ground. |
| 29' | Terrestrial or rock plants |
| 30 | Rhizome not dorsiventral; veins anastomosing in a narrow series of costal areoles (seen at apex of pinna) |
| 30' | Rhizome dorsiventral; veins either free or much anastomosing. |
| 31 | Caudex massive, erect; stipes succulent, with stipule-like outgrowths at their bases; bases of pinnae swollen |
| 31' | Not these characters. |
| 32 | Lamina one or two cells thick apart from midribs of segments of lamina; no stomata. |
| 32' | Lamina throughout more than two cells thick; stomata present. |
| 33 | Sporangia attached to elongating slender receptacles in funnel-shaped pockets at ends of veins. |
| 33' | Sporangia attached to surface of veins |
| 34 | Caudex or rhizome at apex, and bases of stipes, hairy or bristly (no flat scales) or apparently naked. |
| 34' | Caudex or rhizome at apex, and bases of stipes (at least when young) scaly. |
| 35 | Rootstock massive, erect (in a few cases tree-like) or more or less decumbent, radially or- ganized, its apex above ground, bearing a close group of fronds. |
| 35' | Rootstock otherwise, usually entirely below ground. |
| 36 | Fronds simply pinnate; apex of caudex not densely hairy. |
| 36' | Fronds more amply divided; apex of caudex densely hairy. |
| 37 | Aerophores at bases of stipes (sometimes also at bases of pinnae) |
| 37' | Aerophores lacking |
| 38 | Fertile part of frond not leaf-like, erect and attached to base of leafy part |
| 38' | Fertile part of frond leaf-like, sometimes reduced in size as compared with sterile. |
| 39 | Fronds palmately divided; leaflets 3 or 5; veins anastomosing. |
| 39' | Fronds otherwise. |
| 40 | Veins much anastomosing, with free veins in the areoles. |
| 40' | Veins in most cases free; where anastomosing, no free veins in areoles. |
| 41 | Sori quite superficial, on lower surface of lamina, or in a marginal groove. |
| 41' | Sori at ends of veins or on special appendages. |
| 42 | Sori indusiate; fronds fan-shaped or slender and trailing. |
| 42' | Sori not indusiate. |
| 43 | Fronds repeatedly pseudo-dichotomous, with a dormant apex between each pair of branches |
| 43' | Fronds otherwise |
| 44 | Sporangia on special appendages which are at ends of veins of leaflets or attached near apex of frond or of its branches |
| 44' | Sporangia in sori at ends of Single veins or uniting ends of several veins, not on special appendages |
| 45 | Sporangia acrostichoid. |
| 45' | Sporangia not acrostichoid. |
| 46 | Rhizome dorsiventral, creeping on rocks. |
| 46' | Rhizome not dorsiventral, often massive, bearing a tuft of fronds at its apex. |
| 47 | Veins free, or if anastomosing the free veins almost all pointing outwards; spores with perispore |
| 47' | Veins much anastomosing with free veins in areoles pointing all ways; no perispore. |
| 48 | Only the upper pinnae fertile; veins much anastomosing, no free veins in areoles. |
| 48' | Whole frond fertile; in sterile frond veins free or anastomosing otherwise. |
| 49 | Veins free in sterile fronds, or a single row of costal areoles present. |
| 49' | Veins much anastomosing in sterile fronds |
| 50 | Fertile frond simply pinnate |
| 50' | Fertile frond bipinnate |
| 51 | Sorus along edge of lamina, continuous or nearly so. |
| 51' | Sorus otherwise. |
| 52 | Edge of lamina reflexed, protecting sori. |
| 52' | Edge of lamina not reflexed; sorus protected by indusium attached below it, opening towards edge of lamina |
| 53 | Rachis grooved on upper surface, groove open to admit groove of midrib of pinna. |
| 53' | Rachis not so grooved (if grooved, edge of lamina may be decurrent on edge of groove). |
| 54 | Sorus elongate, continuous along each side of costa of pinna. |
| 54' | Sorus otherwise. |
| 55 | Sporangia on surface of reflexed marginal lobes |
| 55' | Sporangia not on such lobes. |
| 56 | Sorus along veins (at least some of them). |
| 56' | Sori not along veins. |
| 57 | Sorus indusiate. |
| 57' | Sorus not indusiate. |
| 58 | Sorus symmetrically divided by line of vein. |
| 58' | Sorus asymmetric, or on one side of vein. |
| 59 | Rachis grooved, groove open to admit groove of branch; scales lacking superficial hairs |
| 59' | Rachis somewhat grooved, groove not open to admit groove of pinna; scales with superficial hairs |
| 60 | Sori along outer veins of costular or costal areoles. |
| 60' | Sori otherwise. |
| 61 | Two strands in stipe, uniting upwards to form a single X-shaped Strand. |
| 61' | Two strands in stipe, uniting upwards to form a single U-shaped Strand. |
| 62 | Sori spreading along all veins of lower surface. |
| 62' | Sori not spreading along all veins. |
| 63 | Slender unicellular hairs present on frond and on scales. |
| 63' | Slender unicellular hairs lacking |
| 64 | Several vascular bundles in stipe |
| 64' | Two vascular bundles at base of stipe, uniting upwards. |
| 65 | Waxy powder on lower surface of lamina |
| 65' | No waxy powder present |
| 66 | Sori at ends of veins, at or close to edge of lamina, each in the base of a cup, or protected by an indusium attached below it or by the reflexed edge of the lamina. |
| 66' | Sori not at ends of veins, or if so not close to edge of lamina. |
| 67 | Sori each in the base of a cup |
| 67' | Sori protected by indusia or by edge of lamina. |
| 68 | Sori protected by indusia opening outwards. |
| 68' | Sori protected by reflexed edge of lamina. |
| 69 | Pinnae articulate to rachis |
| 69' | Pinnae not articulate |
| 70 | An inner indusium also present; rachis grooved, groove open to admit groove of midrib of pinna |
| 70' | An inner indusium lacking; rachis not grooved, or if grooved, edge of pinna decurrent on edge of groove |
| 71 | Rhizome dorsiventral. |
| 71' | Rhizome not dorsiventral. |
| 72 | Sori without indusium. |
| 72' | Sori indusiate. |
| 73 | Fronds lacking dormant apices |
| 73' | Fronds always having some dormant apices |
| 74 | Fronds simple |
| 74' | Fronds pinnately branched |
| 75 | Fronds simple and jointed at base, or pinnate with pinnae jointed to rachis. |
| 75' | Fronds otherwise. |
| 76 | Tree-ferns; sporangia with complete oblique annulus; many vascular bundles in stipe |
| 76' | Not tree-ferns; annulus vertical, interrupted; vascular bundles in a simple ring (except Pleocnemia). |
| 77 | Rachis grooved, groove open to admit groove of branch-rachis or pinna. |
| 77' | Rachis not grooved, or if grooved groove not open to admit groove of branch. |
| 78 | Several vascular bundles in stipe |
| 78' | Two bundles, joining to form one of U-shape. |
| 79 | Hairs (if present) multicellular; scales lacking superficial hairs or glands. |
| 79' | Hairs unicellular; scales bearing superficial hairs or glands |
| 80 | Several vascular bundles in stipe |
| 80' | Two bundles, joining to U-shape |
