1 "Plants rooted in soil or mud, or epiphytic." 2 1 "Plants free-floating." 49 2 "Fertile fronds borne as an offshoot of the sterile fronds, the two parts markedly different; vernation not circinate." Ophioglossaceae 2 "Fertile and sterile fronds borne separately on rhizome, or all fronds fertile; vernation circinate." 3 3 "Sporangia completely enclosed in a sporocarp; sterile leaves filiform or with four leaflets." Marsileaceae 3 "Sporangia borne on the surface of the fronds, often covered by an indusium of the recurved margin of the frond; never completely enclosed by a modified frond (sporocarp)." 4 4 "Stipes with an expanded, stipule-like base; sporangia relatively large, ± sessile, rounded to oval in shape, splitting along a central line." 5 4 "Stipes with base lacking stipule-like structures; sporangia smaller, on short stalks, splitting vertically or laterally." 6 5 "Stipule-like structures fleshy, trunk short (to 80 cm) and massive, with a single crown." Marattiaceae 5 "Stipule-like structures thin; trunk taller, usually with 2 or more crowns." Osmundaceae 6 "Sori on narrow segments borne in pinnate groups at tips of the fertile fronds, or projecting from the margins of the pinnae of fertile fronds." Schizaeaceae 6 "Sori not borne on such projections." 7 7 "Aquatic fern with spongy stipes; fronds strongly dimorphic." Parkeriaceae 7 "Terrestrial or epiphytic ferns." 8 8 "Arborescent ferns." 9 8 "Non-arborescent ferns." 10 9 "Trunk and base of stipes scaly; indusia absent or scale-like." Cyatheaceae 9 "Trunk and base of stipes hairy; sori located in 2-lipped cups, the outer lip formed from the recurved margin of the lamina, the inner lip the true indusium." Dicksoniaceae 10 "Fronds pseudodichotomously branched with dormant apical buds." Gleicheniaceae 10 "Fronds not branching in this manner." 11 11 "Sori ± enclosed by the strongly revolute margins of the pinnae, the fronds long and narrow; rhizomes hairy." Platyzomataceae 11 "Sori marginal or superficial, margins of fronds often recurved but never strongly revolute; rhizomes sometimes hairy." 12 12 "Sori restricted to the marginal or submarginal region of the lamina, if submarginal usually covered by a false indusium." 13 12 "Sori superficial." 26 13 "Rhizomes covered with hairs or bristles." 14 13 "Rhizomes covered with scales." 17 14 "Sporangia borne on a columnar or filiform receptacle within a 2-valved or cupular involucre." Hymenophyllaceae 14 "Sporangia borne on the surface of the lamina." 15 15 "Either sori circular and indusium false and formed from the recurved margin or sori linear and with true indusia present or absent." Dennstaedtiaceae 15 "Sori circular, indusia 2-lipped with the inner lip the true indusium." 16 16 "The 2 lips free, inner membranous and obscure, indumentum on stipe base of long hairs; lamina ± leathery.(Calochlaena)." Dicksoniaceae 16 "The 2 lips fused to form a cup, indumentum on stipe base of very short, dense hairs; lamina soft and membranous." Dennstaedtiaceae 17 "True indusia present." 18 17 "Indusia false (formed by recurved lamina margin) or absent." 20 18 "Indusia cup-like, attached at the base and sides.(Davallia)." Davalliaceae 18 "Indusia flap-like." 19 19 "Sori borne along single veins." Aspleniaceae 19 "Sori borne across the tips of a number of veins." Lindsaeaceae 20 "Epiphytes, leaves simple, linear, rhizome scales clathrate." Vittariaceae 20 "Terrestrial plants, leaves compound; rhizome scales not clathrate." 21 21 "Fronds simply pinnate." 22 21 "Fronds at least 2-pinnate or 2-pinnatifid." 23 22 "Pinnae leathery, veins not readily visible; sori continuous in broad bands along each margin of the pinna.(Pellaea)." Sinopteridaceae 22 "Pinnae herbaceous, veins readily visible; sori continuous in narrow bands." Pteridaceae 23 "Recurved margin covering and bearing the sorus, the whole structure being ± reniform." Adiantaceae 23 "Recurved margin not bearing the sorus." 24 24 "Pinnae rarely >5 cm long; sori and indusia short, sori becoming confluent (indusia sometimes absent).(Cheilanthes)." Sinopteridaceae 24 "Pinnae usually >5 cm long; sori and indusia linear." 25 25 "Rhizomes tufted or short-creeping.(Pteris)." Pteridaceae 25 "Rhizomes long-creeping.(Histiopteris)." Dennstaedtiaceae 26 "Fronds simple." 27 26 "Fronds pinnatifid or more compound." 33 27 "Sori circular." 28 27 "Sori elongated or confluent and covering whole areas of the frond." 29 28 "Fronds articulate on the rhizome, scales of rhizome peltate and/or clathrate." Polypodiaceae 28 "Fronds not articulated, scales of rhizome neither peltate nor clathrate." Grammitaceae 29 "Indusia present." 30 29 "Indusia absent." 31 30 "Indusia parallel with the primary vein." Blechnaceae 30 "Indusia running along the secondary veins." Aspleniaceae 31 "Sporangia borne on the much narrowed tail-like apex of the fertile frond.(Belvisia)." Polypodiaceae 31 "Apex of fronds not very narrow and tail-like." 32 32 "Sporangia scattered, becoming confluent; stipe and lamina bearing stellate hairs.(Pyrrosia)." Polypodiaceae 32 "Sori oblique, usually remaining distinct; stipe and lamina bearing simple or branched hairs." Grammitaceae 33 "Sori elongated along the veins or sporangia scattered over much of the surface of the lamina." 34 33 "Sori circular." 40 34 "Bracket epiphytes with 2 kinds of fronds, green fertile fronds plus brown or green sterile nest-fronds.(Platycerium)." Polypodiaceae 34 "Plants usually terrestrial, fronds of one kind but may be dimorphic." 35 35 "Indusia present." 36 35 "Indusia absent." 38 36 "Sori parallel with the primary and secondary veins of the frond, fronds 1-pinnatifid to 1-pinnate." Blechnaceae 36 "Sori oblique with respect to main vein of the segment, or a main vein lacking; fronds more compound, usually at least 2-pinnatifid." 37 37 "Rhizome scales not clathrate; indusia often double (i.e., one on each side of a vein), especially at the base of the segment." Athyriaceae 37 "Rhizome scales clathrate; indusia always single." Aspleniaceae 38 "Fronds pinnate, segments with distinct petiolules; sporangia covering the entire lower surface of the fertile pinnae.(Acrostichum)." Pteridaceae 38 "Fronds otherwise; sporangia, at least when first formed, along veins." 39 39 "Rhizome scales clathrate, fronds and stipes covered with long hairs.(Pleurosorus)." Aspleniaceae 39 "Rhizome scales not clathrate, fronds glabrous or the lower surface covered with a waxy powder." Taenitidaceae 40 "Fronds delicate and membranous.(Cystopteris)." Athyriaceae 40 "Fronds herbaceous to leathery." 41 41 "Fronds of 2 kinds (green fertile fronds plus brown nest-fronds), veins anastomosing.(Drynaria)." Polypodiaceae 41 "Fronds of 1 kind, but may vary in shape." 42 42 "Rhizomes covered with hairs.(Hypolepis)." Dennstaedtiaceae 42 "Rhizomes covered with scales." 43 43 "Rhizome scales peltate, stipe often articulate on the rhizome." 44 43 "Rhizome scales not peltate, stipe not articulate on rhizome." 45 44 "Fronds pinnatifid (or simple), veins anastomosing; sori large, usually 2 mm or more diam.(Microsorum)." Polypodiaceae 44 "Fronds 1-pinnate or more divided, veins free; sori small, <2 mm diam." Davalliaceae 45 "Fronds pinnatisect.(Doodia)." Blechnaceae 45 "Fronds at least 1-pinnate." 46 46 "Fronds 1-pinnate to 2-pinnatifid (sometimes pinnatifid at apex)." 47 46 "Fronds 2-pinnate or more compound." 48 47 "Pinnae ± oblong in outline, never divided completely into pinnules at the base, veins anastomosing at the bases of the lobes and running to the fork between the lobes." Thelypteridaceae 47 "Pinnae ovate to lanceolate in outline, veins free or copiously anastomosing." Dryopteridaceae 48 "Fronds with lamina membranous, sori without indusium, rhizome scales finely ciliate.(Macrothelypteris)." Thelypteridaceae 48 "Fronds with lamina usually leathery, sori indusiate (except for 1 sp.), rhizome scales entire or finely toothed" Dryopteridaceae 49 "Leaves c. 20 mm long, covered in long papillae." Salviniaceae 49 "Leaves small, 1–2 mm long, imbricate in 2 rows." Azollaceae