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Key to Asplenium

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1 Leaves simple, unlobed (or with a few, irregular forkings in A. septentrionale); veins free or anastamosing-areolate.
  2 Leaf blades 0-3 mm wide, linear, forking or with a few toothlike projections; [V. Schaffneria clade; A. septentrionale subclade]
  2 Leaf blades 10-40 mm wide, lanceolate, lance-attenuate, or oblong.
    3 Leaf apex long-attenuate and characteristically producing plantlets at the tip; veins anastomosing; [V. Schaffneria clade; A. cordatum subclade]
    3 Leaf apex acuminate to obtuse, not producing plantlets at the tip; veins free.
      4 Leaf blade cuneate at base; [of FL southwards]; [III. Neottopteris clade]
      4 Leaf blade cordate at base; [of AL northwards]; [II. Phyllitis clade; Phyllitis subclade].
        5 Longer indusia of each frond avg. 1.2 cm long; leaves (1-) avg. 2.3 (-3.5) dm long; [native in TN, AL, and elsewhere, in natural limestone sinkholes]
        5 Longer indusia of each frond avg. 1.7 cm long; leaves (1-) avg. 3 (-6) dm long; [rarely introduced in North America, typically in artificial settings, such as old well shafts]
1 Leaves pinnatifid (at least in the lower half of the leaf), pinnate, pinnate-pinnatifid, bipinnate, or tripinnate, the apex obtuse, acute, acuminate, or attenuate; veins free.
          6 Rachis shiny black or dark brown throughout its length; rachis not grooved on its upper surface; leaves pinnate, the outline of the leaf blade linear, lanceolate, or oblanceolate, with more-or-less parallel sides for much of its length.
             7 Pinnae orbicular to obovate-oblong, 1-2× as long as wide, the base more-or-less symmetrical (if auriculate, only slightly so and on the side of the pinna toward the base of the leaf); old leaf rachises often with persistent projections left from the disarticulation of the pinnae; [VI. A. trichomanes clade; A. trichomanes subclade].
               8 Sori 4-9 (-12) per pinna, up to 3 mm long; rhizome scales up to 5 mm long; petiole relatively thicker, blackish-brown; pinnae mostly opposite, oblong, spaced more closely, thicker in texture, set at a nearly right angle to the rachis, rarely at all auriculate; spores mostly 34-43 μ long; stomate guard cells mostly 41-49 μ long; [of calcareous rocks]
               8 Sori 4-6 (-9) per pinna, up to 2 mm long; rhizome scales up to 3 mm long; petiole relatively thin, shiny, coppery or bronze; pinnae mostly alternate, suborbicular, spaced more distantly, thinner in texture, set at a fairly oblique angle to the rachis, often slightly auriculate on the side of the pinna toward the leaf base; spores mostly 29-36 μ long; stomate guard cells mostly 38-43 μ long; [mostly of noncalcareous rocks]
             7 Pinnae oblong-rectangular, 2× or more as long as wide, the base asymmetrical or auricled (more prominently auricled on the side of the pinna toward the tip of the leaf); old leaf rachises lacking persistent projections left from the disarticulation of the pinnae.
                 9 Leaves slightly dimorphic, the fertile upright and larger, the sterile spreading and smaller; pinna auricles prominent, often overlapping the rachis; [terrestrial, often not associated with rock outcrops]; [V. Schaffneria clade; A. incisum subclade]
                 9 Leaves not dimorphic; pinna auricles less prominent, usually not overlapping the rachis; [epipetric, always growing in crevices of rock outcrops or in thin soil immediately adjacent to exposed rock]; [VI. A. trichomanes clade; A. monanthes subclade].
                   10 Main vein of the pinna running along the basal edge; sori 1 (-3) per pinna, 1.5-3 mm long, borne along the basal edge, the indusium translucent, whitish, opening toward the leaf tip
                   10 Main vein of the pinna running more-or-less medially; sori 4-10 per pinna (on well-developed pinnae), 1.0-1.5 mm long, borne on both sides of the main vein, the indusium opaque, greenish, opening toward the pinna tip.
                     11 Pinnae margins subentire; pinnae blue-green, coriaceous, borne at right angles to the rachis or slightly reflexed, usually strictly opposite throughout the entire length of the leaf blade
                     11 Pinnae margins shallowly crenate or crenate-serrate; pinnae bright-green, subcoriaceous, borne at right angles to the rachis or ascending, opposite below but usually becoming alternate in the apical 1/3-1/2 of the leaf blade
                       12 Pinna margins crenate to serrate; pinna base lacking an auricle, or the auricle rudimentary; veins evident; spores 64 per sporangium
                       12 Pinna margins shallowly crenate; pinna base with auricle; veins obscure; spores 32 per sporangium
          6 Rachis dull green throughout its length, or at least toward the tip; rachis grooved on the upper surface, at least in the green portion; leaves pinnatifid to tripinnate, the outline of the leaf blade narrowly to broadly triangular, widest at the base (or slightly above the base in A. abscissum) (except A. dentatum).
                          13 Petiole shiny black or brown throughout its length (from base to first leaflet).
                            14 Leaves bipinnate at the base, pinnate-pinnatifid above; spores normal; [XI. Pleurosorus clade; Onopteris subclade]
                            14 Leaves pinnate at the base, pinnatifid above; spores abortive (or normal in A. tutwilerae, known only from Hale County, AL); [V. Schaffneria clade; reticulation between two subclades].
                              15 Spores abortive
                              15 Spores normal; [endemic (as far as known) to Hale County, AL]
                          13 Petiole partially or entirely green (darkened or not at its base).
                                16 Leaves pinnatifid or 1-pinnate through most or all of their lengths (sometimes pinnate-pinnatifid at the base of the leaf).
                                  17 Leaves pinnatifid, sometimes fully pinnate at the base; spores normal
                                  17 Leaves pinnate (sometimes pinnate-pinnatifid at the base of the leaf in A. ×trudellii and A. dentatum); spores normal or abortive.
                                    18 Pinnae 1-8 on each side of the rachis below the merely pinnatifidly lobed upper half of the leaf; blades deltoid to broadly isosceles-triangular, 1-3× as long as wide; [of FL and rarely n. AL].
                                       19 Pinnae 4-8 on each side of the rachis below the merely pinnatifidly lobed upper half of the leaf; basalmost pinnae ca. 3× as long as wide, toothed but not cut; [VIII. Asplenium clade]
                                       19 Pinnae 0-2 (-4) on each side of the rachis below the merely pinnatifidly lobed upper half of the leaf; basalmost pinnae ca. 1.5× as long as wide, both toothed and cut (lobed); [V. Schaffneria clade; A. delavayi subclade]
                                    18 Pinnae 5-35 on each side of the rachis; blades lanceolate or linear, 4-7× as long as wide; [collectively widespread].
                                         20 Pinnae lanceolate, 3-10× as long as wide, with an acroscopic auricle at the base of the larger pinnae; epiphytic on bark; [of FL peninsula]; [I. A. erosum clade]
                                         20 Pinnae ovate, obovate, or deltoid, 1-2.5× as long as wide, lacking an auricle; epipetric; of FL peninsula and also inland from nc. GA and nc. AL northwards].
                                           21 Leaf blade outline with nearly parallel margins, with a blunt tip; spores normal; on moist outcrops of limestone; [of FL peninsula]
                                           21 Leaf blade outline tapering evenly from near or at the base, with a long-attenuated tip; spores abortive; on moist outcrops of felsic sedimentary or metamorphic rocks, such as sandstone, phyllite, schist; [inland from nc. GA and nc. AL northwards]
                                16 Leaves 2-pinnate at least basally, to 3-pinnate.
                                             22 [inland and more northern, from c. AL and c. GA northwards].
                                               23 Petiole darkened toward the base; pinnules toothed, lacerate, pinnatifid, or pinnate; leaves bipinnate to tripinnate, the leaf blades lanceolate-ovate to lanceolate-oblong; ultimate leaf segments sessile or nearly so; [of acidic rocks] ; [XI. Pleurosorus clade; Onopteris subclade]
                                               23 Petiole entirely green; pinnules toothed; leaves bipinnate, the leaf blades ovate-triangular; ultimate leaf segments mostly stalked; [of calcareous rocks]; [XI. Pleurosorus clade; Pleurosorus subclade]
                                             22 [Coastal Plain and southern, of FL]; [VIII. Asplenium clade].
                                                 24 Rachis darkened, at least in its lower portion.
                                                    25 Leaves 2-pinnate basally and pinnate-pinnatifid upwards; spores of different and irregular shapes and sizes
                                                    25 Leaves 2-3-pinnate; spores normal
                                                 24 Rachis green throughout.
                                                      26 Leaves 2-pinnate through most of their length; spores normal
                                                      26 Leaves 2-pinnate only basally, mostly pinnate-pinnatifid to merely pinnate upwards; spores of different and irregular shapes and sizes

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
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