1 Leaf vine-like (with indeterminate growth), 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).

  2 Vine-like leaves scrambling or trailing; sporangia borne 6-12 per sorus

  2 Vine-like leaves twining; sporangia borne singly, each subtended by an indusium-like flap

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).

    3 Leaf blades broadly (about equilaterally) triangular, pentagonal, or flabellate in outline, 0.7-1.3× as long as wide.

      4 Leaf blades flabellate or fan-shaped in outline, the petiole branched once dichotomously, each branch bearing 3-7 pinnae on one side of the rachis only

      4 Leaf blades pentagonal or broadly triangular in outline, the petiole not branched dichotomously.

        5 Leaf blade pentagonal in outline, the terminal pinna the largest; sori either submarginal, roundish, the indusium reniform, or marginal and continuous, covered by a false indusium; [exotic, uncommonly naturalized].

          6 Sori submarginal, roundish, the indusium reniform; leaf blade 2.4-4 dm long and wide

          6 Sori marginal, linear, covered by a false indusium; leaf blade 10-20 dm long and wide

        5 Leaf blade broadly triangular in outline, the basal pinnae the largest; sori marginal, linear, indusium absent, the sporangia either protected by the revolute leaf margin and a minute false indusium (Pteridium), or borne in a stalked, specialized, fertile portion of the blade (Botrypus); [native, collectively common].

             7 Sporangia borne in a stalked, specialized, fertile portion of the blade; texture of mature blades somewhat fleshy; plants solitary from a short underground rhizome with thick, mycorrhizal roots; [primarily of moist forests]

             7 Sporangia borne in marginal, linear sori, indusium absent, the sporangia protected by the revolute leaf margin and a minute false indusium; texture of mature leaf blades hard and stiff; plants colonial from deep-seated rhizomes; [primarily of moist to dry woodlands and savannas]

    3 Leaves elongate in outline, mostly ovate, lanceolate, oblanceolate, or narrowly triangular, 1.5-10× or more as long as wide.

               8 Leaves 2-pinnate or more divided (the pinnae divided to their midribs).

                 9 Leaf blade divided into sterile and fertile portions, the sterile pinnae basal, the sterile pinnules 30-70 mm long and 8-23 mm wide, serrulate, rounded basally, rounded to somewhat acute apically, the fertile pinnae terminal and greatly reduced in size, the fertile pinnules 7-11 mm long and 2-3 mm wide

                 9 Leaf blade not divided into sterile and fertile portions (though often not all pinnules on a leaf bearing sporangia), the sporangia-bearing pinnules only slightly if at all reduced in size, both fertile and sterile pinnules usually 4-20 mm long and 2-10 mm wide.

                   10 Rhizomes long-creeping, leaves scattered, forming clonal patches; vascular bundles in the petiole either 1, U-shaped (even in the lower petiole) or 3 or more; 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 hairs or glabrous to puberulent with glandular trichomes

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

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

                     11 Vascular bundles 2 in the petiole.

                       12 Undersurface of leaf with white or yellow farina (waxy exudate); [FL peninsula]

                       12 Undersurface of leaf green, lacking farina; [collectively widespread]

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

                          13 Leaves 5-25 (-50) cm wide, with scales and minute glands (sometimes also with septate hairs); [native species, widespread].

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

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

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

                              15 Leaves 9-30 cm wide, the tip acute to acuminate; indusium flap-like

               8 Leaves 1-pinnate-pinnatifid or less divided (the pinnae entire, toothed, lobed or pinnatifid).

                                16 Leaves 1-pinnatifid, most of the pinnae not fully divided from one another (the rachis winged by leaf tissue most or all of its length); leaves either dimorphic, the fertile much modified, stiff and/or woody (Onoclea in ONOCLEACEAE or Lorinseria in BLECHNACEAE), or not dimorphic (Pecluma in POLYPODIACEAE).

                                  17 Sporangia borne in circular sporangia on the undersurface of monomorphic leaves; [n. FL southwards]

                                  17 Sporangia borne on modified, stiff and/or woody leaves; [widespread in our area]

                                    18 Fertile leaf stiff but herbaceous, the pinnae linear, not at all bead-like; margins of sterile pinnae finely serrulate, otherwise slightly wavy or straight; pinnae mostly with acute apices, tending to be borne alternate

                                    18 Fertile leaf woody, with bead-like segments; margins of sterile pinnae entire, often wavy or the lowermost even somewhat lobed; pinnae mostly with obtuse apices, tending to be borne opposite

                                16 Leaves 1-pinnate or 1-pinnate-pinnatifid, the pinnae fully divided from one another (the rachis naked for most of its length, often winged in the terminal portion); leaves dimorphic or not.

                                       19 Rhizomes long-creeping, leaves scattered, forming clonal patches.

                                         20 Sori roundish, borne away from the main veins.

                                       19 Rhizomes short-creeping, the leaves clustered, not forming clonal patches (or rhizomes of both types, but leaves borne only in clusters on the short erect ones, in Matteuccia)

                                           21 Plants moderately to very robust, the leaves typically 6-50 dm tall; leaves either strongly dimorphic, the fertile leaves very unlike the sterile, brown at maturity (Matteuccia and Osmundastrum cinnamomeum), or the fertile pinnae very unlike the sterile, brown at maturity, borne as an interruption in the blade, with normal green pinnae above and below (Osmunda claytoniana), or the fertile pinnae toward the tip of the leaf and with sporangia entirely covering the lower surface (Acrostichum); rachises scale-less, petioles scale-less (except at the base in Matteuccia).

                                             22 Leaves 1.5-5 m long; fertile pinnae with sporangia covering the lower surface; [n. FL southward]

                                             22 Leaves 0.6-2.5 m long; fertile portions otherwise.

                                               23 Leaves strongly tapering to the base from the broadest point (well beyond the midpoint of the blade), the basal-most pinnae much < ½ as long as the largest pinnae

                                               23 Leaves slightly if at all tapering to the base, about equally broad through much of their length, the basal-most pinnae much > ½ as long as the largest pinnae

                                           21 Plants mostly less robust, the leaves 3-10 dm tall (except Dryopteris ludoviciana, D. celsa, D. goldiana, and Nephrolepis exaltata to 15 dm); leaves not at all or only slightly dimorphic, the fertile differing in various ways, such as having narrower pinnae (as in Dryopteris ludoviciana, Polystichum acrostichoides, Diplazium, Deparia, and Thelypteris palustris) or the fertile leaves taller and more deciduous (as in Asplenium platyneuron and Dryopteris cristata), but not as described in the first lead; rachises and petioles variously scaly or scale-less, but at least the petiole and often also the rachis scaly if the plants over 1 m tall.

                                                 24 Sori elongate, the indusium elongate, attached along one side as a flap.

                                                    25 Petiole and rachis lustrous brownish-black; fertile leaves 2-8 (-12) cm wide

                                                    25 Petiole and rachis green; fertile leaves 10-20 (-30) cm wide.

                                                      26 Leaves 1-pinnate-pinnatifid (the pinnae pinnatifid)

                                                      26 Leaves 1-pinnate (the pinnae entire)

                                                 24 Sori roundish, the indusium kidney-shaped or roundish, attached by a central stalk.

                                                        27 Leaves 1-pinnate, the pinnae toothed and each with a slight to prominent lobe near the base on the side toward the leaf tip (except Nephrolepis exaltata in NEPHROLEPIDACEAE); indusium peltate (Polystichum in DRYOPTERIDACEAE) or reniform or crescent-shaped (Nephrolepis in NEPHROLEPIDACEAE).

                                                          28 Leaves pale green, thin in texture; pinnae articulate to rachis, deciduous with age; thin, rhizome bearing elongate, thin, wiry stolons; [mostly, if not entirely, exotic in our area, rare]

                                                          28 Leaves dark-green, subcoriaceous to coriaceous; pinnae neither articulate nor deciduous with age; rhizome not producing stolons; [native, common]

                                                        27 Leaves 1-pinnate-pinnatifid, the pinnae pinnatifid, generally lacking a prominent basal lobe; indusium reniform.

                                                            29 Vascular bundles in the petiole 4-7

                                                            29 Vascular bundles in the petiole 2, uniting above