The following key is a traditional dichotomous key and is based on the more conspicuous characters of sporophyte generation. The key can be navigated by the links at each couplet and each family name leades to the coresponding family treatment.
||Plants free floating...
||Plants rooted in the mud or soil beneath water, or in
floating mats of vegetation, or on banks beside water...
||Leaves simple or bilobed, stem short- or long-creeping,
+/- hairy, plants spreading vegetatively by fragmentation; spores of 2 sizes...
||Leaves 2 - 3 - pinnately lobed, stem (rhizome) short
and radial, scaly; sterile fronds sometimes spreading vegetatively by marginal
proliferous buds; spores uniform...
||Expanded leaves large (1 cm or more), simple, borne
in opposite pairs, on the surface of the water, a third lead finely divided
and root-like beneath the water bear the sporocarps...
||Leaves small (c. 1 mm), bilobed, scale-like and overlapping,
roots thin and thread-like...
||Plants fully submerged, rarely exposed for short periods
during dry spells; leaves simple, numerous, long and quill-like, borne on
a compact, radial, corm-like rootstock; spores or 2 sizes...
||Plants generally emergent, or at water margin, or on
floating mats of vegetation; leaves compound, or lobed, or reduced to scale-like
||Plants erect and rush-like, stems pointed and finely
grooved, green, leaves reduced to a whorl of minute brown teeth at each
node; spores green, borne in a terminal cone...
||Plants not rush-like, stems not jointed, fully expanded
leaves present; spores brown or black, produced in variously protected sori
or sporocarps, not cones...
||Leaves divided into 4 equal +/- radial lobes at the
end of a long stalk; spores bornein a capsule-like sporocarp, of 2 sizes...
||Leaves (fronds) pinnately lobed or compound, not 4-patite;
spores borne in thin-walled sporangia variously grouped into sori, uniform...
||High-climbing epiphytes starting from the ground, less
commonly scrambling and thicket-forming in the absence of trees; fronds
pinnate, sterile with close parallel venation with a single series of very
narrow areoles along the midrib, fertile very narrow and completely covered
||Ground ferns with radial or creeping rhizomes, in one
case thicket-forming but never epiphytic; fronds pinnatifid to pinnately
compound, veins freely anastomosing, or in pinnate groups, anastomosing
or not, sporangia borne in discrete or continuous sori on non-contracted
fronds, or if on contracted fronds, protected by the reflexed margin of
||Rhizome +/- erect, sometimes decumbent, radial, woody
or fleshy, plants not stoloniferous; venation freely reticulate without
included free veinlets, not in pinnate groups; sporangia completely covering
the lower surface of pinnae, or on contracted fertile fronds and protected
by the reflexed margin...
||Rhizome creeping, not radial, or if thin and radial
plants spreading by wiry stolons; venation in pinnate groups, free or uniting,
or reticulate with included free veinlets; sporangia borne in discrete +/-
||Large erect plants, stem stout, erect, woody; sporangia
completely covering the entire lower surface of the upper few pinnae, the
pinnae not contracted...
||Plants of moderate size, stem small, fleshy or spongy,
with numerous air canals; sporangia borne on contracted fertile fronds and
protected by the reflexted margin...
||Fronds pinnate; veins forked, free and +/- parallel
to the margin or in pinnate groups, free or uniting with neighbouring groups;
sori small, often protected by an indusium...
||Fronds pinnately lobed or simple with entire margins;
veins feely reticulate, with included free veinlets; sori large, not protected
||Sterile pinnae mostly entire or obscurely toothed, articulate
to the rachis; veins forked, free and +/- parallel to the margin; plants
propagating by wiry rhizomes; sori indusiate...
||Pinnae deeply or shallowly toothed, not articlate to
the rachis; veins in pinnate groups in the lobes, free or united with veins
of adjacent groups to form a single excurrent vein; plants not stoloniferous;
sori indusiate or not...