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 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 0.3-1.6 cm long; sporangia solitary in a marginal pocket on the leaves; leaf texture very thin; rhizome 0.1-0.3 mm in diameter

                            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 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 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