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Keyed in multiple places:

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Key to Dryopteridaceae

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1 Leaf blades pentagonal in outline, ca. 1× as long as wide, the terminal pinna by far the largest; [introduced species, naturalized in moist ravines in SC]
1 Leaf blades lanceolate, oblong, or ovate in outline, 1.5× or more as long as wide.
  2 Costae rounded or flat on the upper surface; costae with dense, multicellular hairs
  2 Costae grooved on the upper surface; costae lacking hairs.
    3 Indusium reniform, attached laterally and with a sinus on one side
      4 Rhizomes creeping, leaves single; leaf blade < 40 cm long
      4 Rhizomes erect or ascending, leaves clustered; leaf blade > 40 cm.
        5 Veins anastamosing, rejoining to form a netlike pattern; pinnae 4-25 pairs per leaf; [non-native, rarely naturalized]
        5 Veins branching dichotomously, free, not rejoining to form a netlike pattern; pinnae 25-50 pairs on larger leaves; [plant a common native species]

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).
               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 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
                                    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).
                                           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 A7: medium to large ‘fern-like’ pteridophytes, terrestrial, growing in soil, not associated with rock outcrops

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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
image of plant
Show caption*© Scott Ward; hood-like flap covering sporangia
  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.
                       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.
                                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 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.
                                       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]
                                               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.
                                                        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]