1 Sporangia discrete, linear; fertile leaves pinnatifid, pinnate, or pinnate-pinnatifid.

  2 Veins of sterile leaves anastomosing; sori distinct from one another, elongate, in end-to-end rows; [subfamily Woodwardioideae].

    3 Leaves dimorphic, the sterile leaves pinnatifid, the pinnae 7-10 pairs per leaf, basally not distinct from one another, the rachis therefore winged by leaf tissue throughout its length, the pinnae merely finely serrulate

    3 Leaves monomorphic; the leaves pinnate-pinnatifid, the pinnae 15-20 pairs per leaf, fully distinct, the rachis therefore not winged by leaf tissue, the pinnae themselves pinnatifid.

      4 Rachis lacking proliferous buds in its upper portion; longer pinnae of a leaf 10-20 cm long; [widespread, native]

      4 Rachis with proliferous buds in its upper portion; longer pinnae of a leaf 20-45 cm long; [rare, exotic]

  2 Veins of sterile leaves free; sori continuous.

        5 Leaf blades usually < 5 dm long; leaves pinnate-pinnatifid in all or part; margins entire (to sparingly and irregularly serrulate); [subfamily Blechnoideae]

        5 Leaf blades usually > 5 dm long; leaves pinnate throughout; margins serrulate; [subfamily Stenochlaenoideae]

1 Leaf vine-like, 0.3-10 m long, the branching dichotomous, 1 branch of each dichotomy terminating in a pair of pinnae, the pinnae often widely spaced (> 10 cm apart)

1 Leaf not vine-like, 0.3-3 m long, the branching not as described above, the pinnae regularly and more-or-less closely spaced (mostly < 10 cm apart).

  2 Leaves (at least the sterile leaves if the leaves are dimorphic) 1-pinnate-pinnatifid or less divided (the pinnae entire, toothed, lobed or pinnatifid).

    3 Leaves monomorphic; sori not covering the undersurface of the leaves.

      4 Sori marginal, continuous, covered by a reflexed false indusium along the leaf margin; pinnae usually opposite, linear, not toothed or lobed

      4 Sori neither marginal nor continuous, slightly to entirely covered by an elongate or roundish indusium (sometimes ciliate, toothed, or divided into narrow segments); pinnae usually at least in part alternate, mostly lanceolate, toothed, lobed, or pinnatifid.

        5 Sori elongate, the indusium flap-like, attached along the side; leaf blades < 7 cm wide when > 30 cm long

        5 Sori circular or globular, the indusium peltate, reniform, or cuplike; leaf blades > 5 cm wide when > 30 cm long.

          6 Leaves pinnatifid

          6 Leaves 1-pinnate or, 1-pinnate-pinnatifid, or 2-pinnatifid.

             7 Leaves 1-pinnate, the pinnae toothed and each with a slight to prominent lobe near the base on the side toward the leaf tip; indusia peltate, reniform, or crescent-shaped.

               8 Leaves pale green, thin in texture; pinnae articulate to rachis, deciduous with age; rhizome bearing elongate, thin, wiry stolons; indusia reniform or crescent-shaped

               8 Leaves dark-green, subcoriaceous to coriaceous; pinnae not articulate and deciduous with age; rhizome not producing stolons; indusia peltate

                 9 Segment margins

                 9 Segment margins serrate or spinulose

             7 Leaves 1-pinnate-pinnatifid or 2-pinnatifid, the pinnae pinnatifid, generally lacking a prominent basal lobe; indusia either reniform or cuplike.

                   10 Vascular bundles in the petiole 3-7

                   10 Vascular bundles in the petiole 2.

                     11 Indusium reniform, arching over the sorus

                     11 Indusium cuplike, attached beneath the sorus and consisting of 3-6 lanceolate to ovate segments

  2 Leaves (at least the sterile leaves if the leaves are dimorphic) 2-pinnate or more divided (the pinnae divided to their midribs).

                       12 Pinnae dimorphic, sori limited to the basal 2 pinnae

                       12 Pinnae not dimorphic.

                          13 Sori marginal and borne on the underside of the false indusium (modified, marginal flaps of the leaf margin); petioles and rachis shiny black or reddish-black; pinnules fan-shaped or obliquely elongate

                          13 Sori not marginal, borne on the undersurface of the leaf blade (if marginal, as in Pteridium and Dennstaedtia, borne on the undersurface of the leaf); petioles darkened only basally (if at all), rachis green, tan, or reddish; pinnules not notably fan-shaped or obliquely elongate.

                            14 Outline of leaf blade narrowed to base, the widest point > 7 pinna pairs above the base, the lowermost pinnae < 1/4 as long as the longest pinnae; rhizomes long-creeping, the leaves scattered or in small tufts, forming clonal patches

                            14 Outline of the leaf blade slightly if at all narrowed to the base, the widest point < 5 pinna pairs from the base, the lowermost pinnae > 1/2 as long as the longest pinnae; rhizomes short-creeping, the leaves clustered, not forming clonal patches (or with rhizomes long-creeping, leaves scattered, forming clonal patches in Dennstaedtia in DENNSTAEDTIACEAE).

                              15 Rhizomes long-creeping, leaves scattered, forming clonal patches; vascular bundles in the petiole 1, U-shaped (even in the lower petiole); sori very small, marginal in sinuses, the indusium cup-like, 2-parted, the outer part a modified tooth of the leaf blade; leaf blades conspicuously puberulent with septate glandular hairs

                              15 Rhizomes short-creeping, the leaves clustered, not forming clonal patches; vascular bundles in the petiole 2-7 (sometimes uniting to 1 in the upper petiole); sori mostly larger, mostly not marginal, the indusium not as above (though cup-like in Woodsia obtusa); leaf blades either glabrous, glabrescent, with flattened scales, or puberulent with glandular trichomes.

                                16 Vascular bundles (3-) 5 (-7) in the petiole

                                16 Vascular bundles 2 in the petiole (or uniting near the leaf blade into 1).

                                  17 Leaves 25-65 cm wide, with whitish, straight, acicular hairs; [species adventive and weedy]

                                  17 Leaves 5-25 (-30) cm wide, with scales and minute glands (sometimes also with septate hairs); [native species].

                                    18 Leaves 1-pinnate-pinnatifid; indusium cup-like, attached beneath the sorus and consisting of 3-6 lanceolate to ovate segments

                                    18 Leaves 2-pinnate-pinnatifid; indusium flap-like, pocket-like, or hood-like, attached at one side of the sorus and arching over it.

                                       19 Leaves 10-30 cm wide, the tip acute to acuminate; indusium flap-like

                                       19 Leaves 4-9 cm wide, the tip long-attenuate; indusium pocket-like or hood-like