General key No 1 to Pteropsida

1. Aquatic plants. 2. Plants floating. Leaves small, simple or bilobed . . . . . . . . . Salviniaceae 2. Plants rooted in earth or on rocks. Leaves larger, more divided. 3. Leaves 4-partite. Sporocarps attached to stipes. . . . . . . . . Marsileaceae 3. Leaves not 4-partite. Sporangia singly or in sori on lower surface of lamina. 4. Sporangia borne singly, protected by reflexed edges of narrow lamina . Adiantum Group 4. Sporangia grouped in sori, on lower surface of lamina, not protected by reflexed edges. 5. Fern of stream-beds in deep shade. Fronds pinnatifid, sori without indusia Polypodiaceae 5. Fern of open swamps. Fronds bipinnatifid, sori indusiate. . . . . Thelypteris Group