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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 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 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 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
............ ............ ............ ............ ..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
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