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Key to Pteridaceae

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1 Gametophytes only present; [subfamily Vittarioideae]
1 Sporophytes present.
  2 Leaves undissected and unlobed, linear, 10-60 cm long and 1-3 mm wide; [subfamily Vittarioideae]
  2 Leaves dissected, not linear, > 20 mm wide.
    3 Sori round or oblong, distinct and separate along the pinnule margins; leaves bright-green, glabrous, herbaceous, delicate, and flexible (darker green, thicker, and hairy in A. hispidulum); [subfamily Vittarioideae]
    3 Sori continuous along the pinnule margins (or across the blade in Acrostichum); leaves mostly dark-green or glaucous, often pubescent, coriaceous, tough, and stiff (except Ceratopteris).
      4 Plant aquatic or subaquatic, pale green, delicate; [subfamily Ceratopteridoideae]
      4 Plant epipetric or terrestrial (except Acrostichum), usually dark or bluish green and coriaceous.
        5 Fertile pinnae with entire lower surface covered by sporangia; leaves 1.5-5 m long; [of wetlands, n. FL southward]; [subfamily Ceratopteridoideae]
        5 Fertile pinnae with sori marginal; leaves < 0.5 m long; [of rocky sites, collectively widespread].
          6 Leaves strongly dimorphic, the fertile leaves obviously longer than the sterile and with narrow elongate ultimate segments; [subfamily Cryptogrammoideae]
          6 Leaves essentially monomorphic.
             7 Petioles with alternating longitudinal grooves (2 or 3) and ridges on the upper surface; [subfamily Pteridoideae].
               8 Lower surface of leaf blades with white or yellow farina; sporangia along the veins, not covered by the reflexed leaf margin; [of peninsular FL in our region]
               8 Lower surface of leaf blades lacking farina; sporangia submarginal, typically covered by the reflexed leaf margin; [widespread in our region]
             7 Petioles rounded, flattened, or with a single groove on the upper surface; [subfamily Cheilanthoideae].
                 9 Leaves 1-pinnate or 1-pinnate-pinnatifid; lower leaf blade surfaces densely covered with stellate and ciliate-fringed scales; petiole with 2 vascular bundles
                 9 Leaves 1-pinnate-pinnatifid or more divided (to 5-pinnate); lower leaf blade surfaces glabrous to pubescent and/or farinose; petiole with 1 vascular bundle.
                   10 Lower leaf surface with dense white farina.
                     11 Leaf blade deltoid; white farina on lower blade surface not interspersed with shiny, dark-brown needle-like hairs; [of KY westwards]
                     11 Leaf blade lanceolate; white farina on lower blade surface interspersed with shiny, dark-brown needle-like hairs; [of s. TX only in our region]
                   10 Lower leaf surface not farinose, variously glabrous or hairy; [widespread in our region].
                       12 Leaf blade pentagonal in outline, divided into 3-5 segments which are each merely pinnatifid
                       12 Leaf blade lanceolate or ovate in outline, 1-5-pinnate.
                          13 Leaves 1-3-pinnate, the ultimate leaf-segments 8-100 mm long, glabrous or sparsely and inconspicuously hairy
                            14 Petioles slightly grooved or flattened and ultimate segments thin in texture and not strongly rolled, and also lacking a mucro or cusp at apex
                            14 Petioles either terete (not grooved/flattened), or petiole flattened, and then the ultimate segments also leathery and strongly rolled and with mucronate apex
                          13 Leaves 2-5-pinnate, the ultimate leaf-segments 1-4 (-8) mm long, more-or-less densely hairy (glabrous or glabrescent in Myriopteris alabamensis and M. microphylla).
                              15 Ultimate leaf segments cordate at the base and well-separated from one another on prominent stalks [of ec. TX only in our region]
                              15 Ultimate leaf segments never cordate, approximate to one another

Key A4: small ‘fern-like’ pteridophytes, epipetric or epiphytic, growing on rock, tree bark, or walls

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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]
                                       19 Leaf blade broadly triangular in outline, the basal pinnae by far the largest; rhizome ca. 1 mm in diameter; indusia absent; [native species of mountain peaks from n. NC and VA northwards]
                            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 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

Key A5: small ‘fern-like’ pteridophytes, terrestrial, growing in soil, not associated with rock outcrops

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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 normal leaf blades
               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

Key A6: medium to large ‘fern-like’ pteridophytes, epipetric on rock or walls, or epiphytic on tree trunks

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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 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