1 Leaf blades 7-25 (-30) cm long, triangular, < 2× as long as wide (or lanceolate and > 4× as long as wide in the rarely naturalized P. decursive-pinnata); rachis with adnate wings between the pinnae; sori without indusia; midribs of pinnae lacking an adaxial groove; [subfamily Phegopteridoideae]; [Phegopteroid clade]

1 Leaf blades (15-) 20-100 cm long, lanceolate, oblong-lanceolate, or triangular, > 2× as long as wide; rachis without adnate wings between the pinnae; sori with reniform indusia; midribs of pinnae with an adaxial groove (adaxial groove lacking in Macrothelypteris).

..2 Midribs of the pinnae lacking an adaxial groove; leaf bipinnate to tripinnate; [subfamily Phegopteridoideae]; [Phegopteroid clade]

..2 Midribs of the pinnae with an adaxial groove; leaf pinnate to pinnate-pinnatifid; [subfamily Thelypteridoideae.

....3 Leaves 1-pinnate (the pinnae entire or serrate, and also often undulate); veins forming parallel rows of more than 5 areoles between the pinna margin and the main vein, the areoles with a single excurrent, free veinlet; sori elongate; [Goniopteroid clade]

....3 Leaves 1-pinnate-pinnatifid (the pinnae lobed to pinnatifid); veins all free or at most with a single areole between the sinus and the main vein; sori round or reniform (elongate in Leptogramma).

......4 Stellate hairs present on rachis, veins, and upper leaf blade surface; [n. FL south to s. FL]; [Goniopteroid clade]

......4 Stellate hairs absent; [collectively widespread].

........5 Sori elongate; sporangia with hairs 0.1-0.2 mm long; [endemic to nc. AL]; [Stegnogrammoid clade]

........5 Sori round or slightly longer than wide; sporangia glabrous; [collectively widespread].

..........6 Basal veins from adjacent lobes of the pinna not meeting at all; lowermost pinnae pinnae of a leaf either as long as the pinnae above (or only slightly smaller), or strongly reduced (with an obvious and strong taper of the blade outline towards the base).

............ 7 Lowermost pinnae of a leaf as long as the pinnae above, or only slightly smaller (> 80% as long).

............ ..8 Veins of the pinna-lobes unbranched; lower leaf surface with sessile, reddish, resinous glands; lower surface of costae lacking scales; [montane w. NC and e. TN northeastwards]; [Amauropeltoid clade]

............ ..8 Veins of the pinna-lobes mostly Y-forked; lower leaf surface lacking glands; lower surface of costae with persistent ovate scales; [widespread in our region]; [Thelypteroid clade].

..........6 Basal veins from adjacent lobes of the pinna either uniting either below the sinus (between the sinus and the costa) and therefore forming a united vein continuing to the sinus, or reaching the sinus at the same point; lowermost pinnae of a leaf as long as the pinnae above, or only slightly smaller (> 80% as long) (except in Christella); pinnae 3.5-45 cm long, usually at least the longer > 15 cm long (except in Christella).

............ ....9 Basal veins from adjacent lobes of the pinna reaching the sinus at the same point (but not uniting to form a united vein to the sinus); rhizomes 3-6 mm in diameter.

............ ......10 Lower leaf surface with sessile, opaque, sulfur-colored or pale yellow glands (obvious without magnification); [Sphaerostephanoid clade]

............ ......10 Lower leaf surface lacking sessile glands (sometimes short-stipitate light yellowish glands present)

............ ....9 Basal veins from adjacent lobes of the pinna uniting below the sinus (between the sinus and the costa) and therefore forming a united vein continuing to the sinus (this easiest to see on the upper surface of the leaf); rhizomes 3-12 mm in diameter.

............ ........11 Lowermost pinnae reduced, smaller than some of those above; costae abaxially lacking scales; blades abaxially lacking glands or with short-stipitate, light yellow or orangish glands; rhizomes relatively short-creeping, brown, scaly; ]Pseudocyclosoroid clade]

............ ........11 Lowermost pinnae the longest or nearly so; costae abaxially with ovate scales; blades abaxially with sessile orangish or reddish, hemispherical glands; rhizomes very long-creeping, blackish, nearly naked; [Goniopteroid clade]

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 dimorphic, the sterile leaves 1-pinnate, the fertile leaves bipinnate; sori covering the entire undersurface of the fertile leaves

....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 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