NOTABLE FERN FAMILIES
OSMUNDA (Flowering Ferns)
Tall swamp ferns, growing in large crowns, with the fertile fronds or portions conspicuously unlike the sterile; sporangia opening by a longitudinal cleft into two valves.
Coarse ferns, with the fertile fronds rolled up into necklace-like or berry-like segments, and entirely unlike the broad, pinnatifid sterile ones. Fertile fronds unrolling at maturity, allowing the spores to escape, and remaining long after the sterile fronds have perished; sporangia stalked, ringed, bursting transversely.
Small or medium-sized ferns, growing among rocks, with 1–2 pinnate or pinnatifid fronds and round fruit-dots; indusium thin and often evanescent, attached by its base under the sporangia, either small and open, or else early bursting at the top into irregular pieces or lobes; sporangia stalked, ringed, bursting transversely.
CYSTOPTERIS (Bladder Ferns)
Delicate rock or wood ferns, with 2–3 pinnate fronds and round fruit-dots; indusium hood-like, attached by a broad base to-the inner side, soon thrown back or withering away; sporangia as above.
ASPIDIUM (Shield Ferns)
Ferns with 1–3 pinnate fronds and round fruit-dots; indusium more or less flat, fixed by its depressed centre; sporangia as above.