Key to Families: 1. Plants floating or submerged aquatics (sometimes appearing terrestrial when present in drying vernal pools), with or without floating leaf blades. … 2. 1.’ Plants not floating or submerged aquatics (if submerged then only ephemerally so and not restricted to those conditions), leaf blades various. … 4. 2. Plants floating aquatics, not rooting in soil. … Salviniaceae 2.’ Plants rooted in soil, not floating. … 3. 3. Leaves all fertile, linear, in dense rosettes from subterranean corm, each with sporangium imbedded in base. … Isoetaceae 3.’ Leaves of two forms, one linear with 0-4 fan-shaped pinnae at apex, the other modified into a bean-shaped sporocarp that is submerged and on a short stalk near the rhizome. … Marsileaceae 4. Stems grooved lengthwise and jointed at nodes; spores in terminal, fleshy cones. … Equisetaceae 4.’ Stems not grooved lengthwise or jointed at nodes; spores in leaf axils or underside of leaf surface. … 5. 5. Plants moss-like, leaves simple and needle-like; spores in leaf axils … Selaginellaceae 5.’ Plants fern-like, leaves compound or pinnately lobed; spores on underside of leaf surface. … 6. 6. Plants with leaves split into separate vegetative and reproductive sections. … Ophioglossaceae 6.’ Plants with leaves not separated into distinctive vegetative and reproductive parts. … 7. 7. Spore clusters (sori) near the leaflet margins, appearing elongate, usually at least partially covered by the in-rolled or curled leaflet margins. … 8. 7.’ Sori on or along veins between leaflet margin and midrib, mostly round in outline; leaflet margins usually flat, rarely inrolled or curled. … 9. 8. Generally 5-20 dm tall, sori continuous on leaf edge and covered by inrolled margin. … Dennstaedtiaceae 8.’ Generally less than 2 dm, if taller then sori covered by individual reflexed lobe tips of the leaf segments. … Pteridaceae 9. Indusium peltate or kidney-shaped. … Dryopteridaceae 9.’ Indusium absent, or if present then a hyline flap along vein margin, or segmented in sections, sometimes hair-like, never peltate or kidney-shaped. … 10. 10. Leaves divided to once-pinnate. … Polypodiaceae 10.’ Leaves twice-pinnate or more. … 11. 11. Leaves 2-8 dm; persistent petiole bases course, flattened, at least 3 mm wide. … Athyriaceae 11.’ Leaves not more than 3.5 dm; petioles less than 2 mm wide. … 12. 12. Veins on leaf blades extenting to margin (very noticable on adaxial side up leaf); petiole bases not persistent. … Cystopteridaceae 12.’ Veins on leaf blades not extending to margin (sometimes veins hard to see on adaxial side of leaf); petiole bases persistent. … Woodsiaceae