1. Plant free-floating, raft-like, or stranded along shoreline or on drying mud
2. Lvs 0.5–1.5 mm, alternate [each with a thick green or ± red-tinged floating lobe and a thin, colorless submersed lobe]; upper surface of floating lobe papillate or with short, inconspicuous hairs ..... AZOLLACEAE {G2}
2' Lvs 5–25 mm, appearing opposite [actually 2 floating leaves plus a 3rd submersed leaf dissected into root-like lobes]; upper surface of floating leaves conspicuously hairy ..... SALVINIACEAE {G2}
1' Plant anchored in soil or growing on another plant [if plant aquatic, rooted in bottom sediments]
3. Lvs linear or scale- or needle-like, entire or toothed (sometimes divided into linear lobes in Asplenium septentrionale); veins generally 0 or 1 (–few in Asplenium septentrionale)
4. Lvs basal, linear
5. Sporangia in 1 or more linear sori on abaxial leaf face ..... ASPLENIACEAE (Asplenium septentrionale)
5' Sporangia underground, embedded in adaxial face of widened leaf base or enclosed in hard, spheric sporangium case near leaf base
6. Plant tufted, base corm-like; new leaves erect, never coiled; sporangium solitary, embedded in adaxial face of widened leaf base, ± covered by a translucent membrane ..... ISOETACEAE {G2}
6' Plant creeping by rhizomes; new leaves ± coiled, unrolling as they develop; sporangia several, enclosed in short-stalked, hard case attached near leaf base ..... MARSILEACEAE (Pilularia) {G2}
4' Lvs cauline, scale- or needle-like; sporangia in cone at tip of aerial shoot or in axils of distal leaves
7. St hollow, jointed at nodes; leaves whorled, fused at base; sporangia several on undersides of peltate structures that are clustered in terminal cone ..... EQUISETACEAE {G2}
7' St solid, not jointed; leaves alternate or opposite; sporangia in axils of distal scale-like leaves, the aggregation of fertile leaves sometimes cone-like
8. Fertile leaves not in well defined ranks, the aggregation appearing round when viewed along axis from tip; sporangia all of 1 kind, producing only 1 kind of spore ..... LYCOPODIACEAE
8' Fertile leaves 4-ranked, the aggregation appearing square when viewed along axis from tip; sporangia of 2 kinds, some with 4 large spores and others with many small spores ..... SELAGINELLACEAE
3' Lvs with well developed blades, not linear or scale- or needle-like, often lobed or compound; veins many
9. Plant aquatic or in dried pools or creek beds; leaf palmately compound, leaflets 4; sporangia borne underground or underwater, enclosed in short-stalked, hard case attached near petiole base ..... MARSILEACEAE (Marsilea) {G2}
9' Plant terrestrial or strongly emergent if in wet soil, or growing on another plant; leaf simple or 1–4-pinnate, if compound, leaflets generally >> 4; sporangia borne on aerial portion of leaf
10. Lf divided into dissimilar sterile (trophophore) and fertile (sporophore) parts; sterile part with an entire or 1–3-pinnate blade; fertile part bladeless, sporangia borne in stalked cluster arising from petiole or blade base; new leaves never coiled ..... OPHIOGLOSSACEAE
10' Lf not divided into dissimilar sterile and fertile parts; sporangia borne on underside of leaf blade, sometimes near margin; new leaves generally coiled, unrolling as they develop
11. Lvs of 2 dissimilar kinds, the fertile (sporangium-bearing) blades with greatly narrowed segments
12. Blade deeply pinnately lobed or 1-pinnate; leaf generally > 30 cm ..... BLECHNACEAE (Blechnum)
12' Blade 2 or more × pinnate or divided; leaf <= 30 cm ..... PTERIDACEAE (4)
11' Lvs all alike or nearly so, the fertile [sporangium-bearing] blades very similar in size and shape to sterile blades
13. Sori borne along or near margin of leaf; indusia 0 or sori covered by reflexed or recurved leaf margin or leaf margin segment
14. Pinnae all entire or minutely toothed ..... PTERIDACEAE (4)
14' Pinnae [some or all of them] conspicuously toothed or lobed
15. Rhizome and base of petiole covered by hairs; rhizome long-creeping; leaf often > 80 cm, sometimes >= 2 m — blade widely triangular, 2–4-pinnate ..... DENNSTAEDTIACEAE
15' Rhizome and base of petiole bearing linear to ovate scales; rhizome short and compact to long-creeping; leaf generally < 80 cm, often much shorter ..... PTERIDACEAE (4)
13' Sori borne away from margin on underside of leaf or leaflet, or sporangia scattered along veins and not clustered into sori; indusia present or 0
16. Sporangia scattered along veins, not clustered into distinct sori; indusia 0 ..... PTERIDACEAE (4)
16' Sporangia clustered in distinct sori; indusia sometimes present
17. Indusia 0
18. Blade deeply pinnately lobed ..... POLYPODIACEAE
18' Blade 2–3 pinnate ..... WOODSIACEAE (Athyrium distentifolium var. americanum)
17' Indusia present
19. Sori linear to oblong or J-shaped
20. Veins of leaf segment forming a network; sori generally 2–4 mm, linear-oblong, end-to-end in rows parallel to midvein of leaf segment — leaves 1 pinnate with deeply pinnately lobed pinnae ..... BLECHNACEAE (Woodwardia)
20' Veins of leaf segment free, minor veins extending to segment margin without rejoining; sori 0.5–15 mm, linear, oblong, J-shaped, or reniform, not end-to-end in rows parallel to midvein of leaf segment
21. Lf 3–30 cm, 1-pinnate with pinnae < 1.5 cm or leaf simple, linear, undivided or forked ..... ASPLENIACEAE
21' Lf 20–200 cm, 1–2 pinnate with pinnae generally 5–25 cm, toothed or pinnately lobed ..... WOODSIACEAE (Athyrium filix-femina var. cyclosorum)
19' Sori ± round
22. Blade with 1-celled, clear, needle-like hairs ..... THELYPTERIDACEAE
22' Blade without needle-like hairs
23. Indusium peltate or round-reniform, attached ± in center of sorus, generally present and readily observable in late-season specimens ..... DRYOPTERIDACEAE
23' Indusium attached to one side of sorus or cup-like, attached beneath sorus and often of hair- or scale-like fragments or lobes, generally delicate, often difficult to observe in late-season specimens ..... WOODSIACEAE (2)
