1 Leaves pinnatifid or bipinnatifid, the pinnae not fully divided from one another (the rachis winged by leaf tissue most or all of its length).

  2 Leaves pinnatifid, the pinnae not lobed.

    3 Leaf blades with a long-attenuate apex, blade lobed for up to 2/3 its length; sori elongate

    3 Leaves without a long-attenuate apex, blade lobed for > 4/5 of its length; sori round

  2 Leaves bipinnatifid, at least the lowermost pinnae deeply lobed.

      4 Leaves of a very delicate texture, 1 cell thick; sori borne in cups on the leaf margins; [rock outcrops with high air humidity]

      4 Leaves of an herbaceous, subcoriaceous, or coriaceous texture, > 1 cell thick; sori otherwise; [various habitats, not strictly of moist sites].

        5 Leaf blades 1-7 cm long, hairy with some hairs > 1 mm long

        5 Leaf blades > 7 cm long, glabrescent or hairy with hairs < 1 mm long.

          6 Lowermost (and other) pinnae with numerous, rather even lobes

          6 Lowermost pinnae with a few, irregular lobes (the upper pinnae unlobed)

1 Leaves pinnate, pinnate-pinnatifid, 2-pinnate, or even more divided, to 5-pinnate (the rachis naked for most of its length, often winged in the apical portion).

             7 Leaves pinnate or pinnate-pinnatifid.

               8 Leaves of a very delicate texture, 1 cell thick; sori borne in cups on the leaf margins; [rock outcrops with high air humidity]

               8 Leaves of an herbaceous, subcoriaceous, or coriaceous texture, > 1 cell thick; sori otherwise or sporangia not grouped in sori; [various habitats, not strictly of moist sites].

                 9 Pinnae > 1 cm wide; leaves subcoriaceous to coriaceous

                   10 Sporangia borne on 2 specialized fertile pinnae (in rows on segments of the 2 basalmost fertile pinnae of the leaf); [native; TX westwards]

                   10 Sporangia borne on the lower surface of green leaves; [collectively widespread]

                     11 Veins free; [native; s. FL]

                     11 Veins anastamosing (rejoining one another) to form a netlike pattern of areoles.

                       12 Costae with a groove on the upper side, sometimes with tan, filiform scales; margins of segments denticulate, crenate, or spinulose

                       12 Costae rounded or flat on the upper side, with red, multicellular hairs; margins of segments entire or with rounded lobes

                 9 Pinnae < 1 cm wide; leaves herbaceous to subcoriaceous.

                          13 Sori on the undersurface of the leaf, located away from the margins

                          13 Sori on the undersurface of the leaf, marginal and more-or-less hidden beneath either the unmodified revolute leaf margin or under a modified, reflexed false indusium

             7 Leaves bipinnate or more divided.

                            14 Leaf blade pentagonal, broadly triangular, or narrowly triangular in outline, ca. 1-2.5× as long as wide.

                              15 Leaf blade narrowly triangular in outline, mostly 2-2.5× as long as wide.

                                16 Sporangia borne either in many sori on fertile blades or on fertile pinnules borne at the base of the otherwise sterile blades

                                16 Sporangia borne in a solitary sorus terminal on the truncate apex of wedge-shaped leaf segments

                              15 Leaf blade either ovate, pentagonal, or broadly triangular in outline, mostly 0.8-2× as long as wide.

                                  17 Leaves dimorphic, fertile leaves with longer and narrower segments than the sterile leaves

                                  17 Leaves monomorphic.

                                    18 Leaf segments strongly revolute; sporangia scattered along veins or submarginal, not grouped into indusiate sori; lower surface of leaf segments either densely covered with a whitish farina or distinctly bluish-green

                                    18 Leaf segments planar; sporangia borne in round, indusiate sori; lower surfaces of leaf segments green.

                                       19 Leaf blade pentagonal in outline, the terminal pinna by far the largest; rhizome 5-8 mm in diameter; indusia present, thick, persistent, and reniform; [introduced species, rarely naturalized]

                            14 Leaf blade elongate, mostly lanceolate, generally > 4× as long as wide (except in Adiantum, with leaf blade often only 1.5-3× as long as wide, but not notably triangular or pentagonal in outline).

                                         20 Sori marginal, usually more-or-less hidden under the revolute margin of the pinnule

                                         20 Sori not marginal, either exposed, or slightly to strongly hidden by indusia.

                                           21 Leaf blades 3-12 cm long; sori elongate, covered by a flap-like, entire indusium

                                           21 Leaf blades 4-30 (-50) cm long; sori globular, surrounded or covered by an entire, ciliate, or divided indusium.

                                             22 Veins reaching the margin; indusium attached under one side of the sorus, hood-like or pocket-like, arching over the sorus; petioles glabrous or sparsely beset with scales, the petiole bases not persistent

                                             22 Veins ending short of the margin; indusium attached under the sorus, either cup-like (divided into 3-6 lanceolate to ovate lobes which surround the sorus from below) or of minute numerous septate hairs, which extend out from under the sorus on all sides; petioles often densely beset with scales, the petiole bases persistent

1 Leaf blades appearing to be digitate (the segments arising at a single point); [FL peninsula]

1 Leaf blades pinnate or pinnatifid (in various degrees); [collectively widespread]

  2 Petiole branched once dichotomously, each branch then bearing 3-7 pinnae on the same side of the 2 rachis branches, the overall outline of the blade in the shape of a fan and often broader than long

  2 Petiole not branched dichotomously, the outline of the blade either longer than broad or triangular and about as wide as long.

    3 Leaves pinnatifid or bipinnatifid, most of the pinnae not fully divided from one another (the rachis winged by leaf tissue most or all of its length).

      4 Sporangia borne on an erect stalk that arises at or above ground level from the petiole of the sterile leaf blade (joining the petiole of the sterile leaf above the rhizome)

      4 Sporangia either borne on normal leaf blades or on specialized (fertile) leaves separate from the rhizome.

        5 Leaves monomorphic, the sori borne on normal leaf blades

        5 Leaves dimorphic, the sori borne on leaves significantly different from normal leaves.

          6 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 oppositely

          6 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 alternately

    3 Leaves pinnate, pinnate-pinnatifid, 2-pinnate, or even more divided (the rachis naked for most of its length, often winged in the apical portion).

             7 Leaves broadly triangular in outline, about as broad as long.

               8 Sporangia borne on an erect stalk that arises at or above ground level from the petiole of the sterile leaf blade (joining the petiole of the sterile leaf above the rhizome)

             7 Leaves lanceolate in outline, definitely longer than broad; sporangia either borne on normal leaf blades, or on slightly dimorphic blades, or on the basalmost pinnae of the leaf, or on an erect stalk that arises at or above ground level from the petiole of the sterile leaf blade (joining the petiole of the sterile leaf above the rhizome).

                 9 Leaf blades 1-8 cm long; sporangia borne on an erect stalk that arises at or above ground level from the petiole of the sterile leaf blade (joining the petiole of the sterile leaf above the rhizome)

                 9 Leaf blades 10-30 (-100) cm long; sporangia either borne on normal leaf blades, or on slightly dimorphic blades, or on basalmost pinnae of the leaf.

                   10 Leaves dark green, subcoriaceous in texture, evergreen

                   10 Leaves light to medium green, herbaceous in texture, deciduous to semi-evergreen.

                     11 Sori continuous along the midrib of the pinna.

                     11 Sori distinct.

                       12 Sori elongate; leaf blades somewhat dimorphic, the fertile larger and erect, the sterile smaller and prostrate, the larger leaf blades 2-4 (-6.5) cm wide; petiole with 2 vascular bundles, uniting upwards into 1 ×-shaped bundle

                       12 Sori round; leaf blades monomorphic (or slightly dimorphic in Cystopteris); the larger leaf blades 5-15 cm wide; petiole with 2 vascular bundles, uniting upwards into 1 U-shaped or V-shaped bundle.

                          13 Leaf vestiture nearly lacking (if present, not of unicellular acicular hairs or gland-tipped hairs)

                          13 Leaf vestiture of unicellular acicular hairs 0.2-1 mm long intermixed with short-stalked or sessile yellowish glands