1 Stem obviously jointed; leaves scale-like, borne in a whorl at each of the distant joints; spores borne in a terminal strobilus with peltate scales

1 Stem (or rhizome) not jointed; leaves scale-like or larger, but if scale-like not borne in whorls at distant joints; spores borne variously, but if in a terminal strobilus the scales not peltate.

  2 Leaves linear, grass-like, 1-60 cm long, 20× or more as long as wide.

    3 Leaves solitary (though often the internodes very short from a thin, creeping rhizome); sporangia borne in a spherical (ca. 3 mm in diameter) sporocarp on a separate branch from the rhizome

    3 Leaves numerous from a corm or short-creeping rhizome; sporangia either borne in the expanded leaf bases (Isoetes in ISOETACEAE) or in 2 rows at the tip of the linear fertile leaves (Schizaea in SCHIZAEACEAE), or in a sub-marginal groove on either side of the midrib (Vittaria in PTERIDACEAE).

      4 Leaves straight and stiff, arching, or flaccid, from a 2-3-lobed corm; sporangia borne in the expanded, hyaline leaf bases

      4 Leaves either straight and stiff or notably spiral-curly, from a short-creeping rhizome; sporangia borne in 2 rows either at the expanded pectinate tip of the fertile leaves or along much of the length of the linear leaves.

        5 Leaves 10-60 cm long, straight, stiff; plants epiphytic or rarely epipetric, the leaves pendent

        5 Leaves 1-12 cm long, spiral-curly; plants terrestrial in peaty substrate, the leaves erect

  2 Leaves various (scale-like, awl-like, moss-like, or flat), but not linear and grass-like, mostly 1-10 (-20)× as long as wide.

          6 Leaves inconspicuous, reduced to a few nerveless scales (< 1.5 mm long), the internodes much longer than the leaves; sporangia yellowish, 3-locular, 1-2 mm in diameter; stems upright, repeatedly branched dichotomously

          6 Leaves either larger or, if scale-like, with 1 or more nerves and longer than the internodes (the leaves thus overlapping); sporangia yellowish to brownish, 1-locular, < 1 mm in diameter; stems either subterranean or surficial rhizomes or erect or ascending (and sometimes dichotomously branched in whole or in part in Huperzia in HUPERZIACEAE, and Diphasiastrum and Dendrolycopodium in LYCOPODIACEAE).

             7 Plant with leaves very numerous and overlapping along the creeping, ascending, erect, or pendant stems, the leaves scale-like or awl-like, 0.5-2 (-3) mm wide, typically acute, acuminate, or hair-tipped; sporangia either in terminal strobili (axillary to specialized, smaller leaves) or axillary to normal leaves; [Lycophytes].

               8 Sporangia borne in flattened or quadrangular strobili sessile at the tips of leafy branches; spores and sporangia each of two sizes, the megasporangia larger and borne basally in the strobili

               8 Sporangia borne either in the axils of normal foliage leaves, or in strobili sessile at the tips of leafy branches or stalked on specialized branches with fewer and smaller leaves; spores and sporangia each of one size.

                 9 Leafy stems erect or pendant, simple or dichotomously branched, the ultimate branches vertically oriented (upwards or downwards); sporophylls like the sterile leaves or only slightly reduced, in annual bands along the stem; vegetative reproduction by leafy gemmae near the stem apex (Huperzia) or lacking gemmae (Phlegmariurus)

                 9 Leafy stems prostrate or erect, if erect then generally branched, the ultimate branches spreading (horizontal) or ascending; sporophylls differing from sterile leaves, either broader and shorter, or more spreading, aggregated into terminal cones; lacking vegetative reproduction by gemmae.

             7 Plant with leaves not as above (see below for details); [Pteridophytes].

                   10 Leaves palmately lobed.

                     11 Leaves divided into separate sterile and fertile segments, the sterile leaf blade 30-90 cm long, ovate to lanceolate, entire-margined, obtuse, the longer fertile portion with 2 rows of sporangia somewhat imbedded in it

                     11 Leaves with fertile portions in patches near the tips of the lobes

                   10 Leaves unlobed (or if lobed, pinnately so).

                       12 Plant with 1 (-several) leaves, divided into separate sterile and fertile segments, the sterile leaf blade 0.3-90 cm long, ovate to lanceolate, entire-margined, unlobed, obtuse, the longer fertile portion with 2 rows of sporangia somewhat imbedded in it

                       12 Plant with many leaves, generally 5 or more, not divided into separate sterile and fertile segments, the leaves either (a) small, 0.3-1.6 cm long, obovate, scattered along a very thin creeping rhizome, or (b) larger, (2-) 8-30 cm long, cordate at base, the tip long-attenuate (often proliferous, bearing a plantlet at the tip).

                          13 Leaf blades (2-) 8-30 cm long, cordate at the base, the tip long-attenuate, often proliferous (bearing a plantlet at the tip); sporangia grouped into indusiate sori on the undersurface; leaf texture moderately thick; rhizome erect or ascending, 1.0-1.5 mm in diameter, the leaves clustered from its tip

                          13 Leaf blades 0.3-15 cm long, cuneate at the base, acute to rounded or obtuse at the tip, not proliferous; sporangia solitary in a marginal pocket on the leaf; leaf texture very thin; rhizome creeping on the surface of rock or bark, either 0.1-0.3 or 0.5-1.5 mm in diameter, the leaves scattered along it

                            14 Leaf blades 2-15 cm long; sporangia borne in round sori on the lower surface of the leaves; leaf texture herbaceous to subcoriaceous; rhizome 0.5-1.5 mm in diameter

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 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 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 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