Sensitive Fern (Onoclea sensibilis)

Family:

Fern Family (Polypodiaceae)

Other Names:

bead fern, meadow brake.

Origin and Distribution:

Sensitive fern is a native species common throughout northeastern and central North America. It grows in damp, wet areas in meadows, along wood edges, on banks and along walls, doing well in either full sun or shade.

Plant Description:

Sensitive fern is a perennial fern that has a rather unfernlike appearance. This species can grow 2 feet tall, and is characterized by its beaded fertile leaves that turn dark brown at maturity. Sensitive fern is a primitive perennial. Unlike our more typical broadleaf perennials, sensitive fern lacks true stems, and each leaf arises directly from the rhizome (horizontal underground stem), supported on a rigid leaf stalk. In addition, it does not produce flowers or seeds. Instead, sensitive fern reproduces by spores and creeping rhizomes.

  • Root System:

    Creeping rhizomes (horizontal underground stems) grow near the soil surface, and are stout, brown, smooth and extensively branched. Numerous roots grow along the rhizomes and produce a fibrous mat.

  • Seedlings and Shoots:

    The curled leaves (fiddleheads) emerging from rhizomes form a distinctive, pale red mass in the spring.

  • Stems:

    The erect leaf stalk (not a true stem) is brittle, yellow, and mostly smooth, with a brown, thickened base. The stalk is usually longer than the leaf, and has a shallow furrow in front.

  • Leaves:

    Leaves are of 2 types, sterile (vegetative) and fertile (reproductive), and are produced on separate stalks. STERILE LEAVES (Approximately 2 feet tall) are light green, leathery, broad, and almost triangular, and are tilted up and back. They are composed of 12 nearly opposite leaflets with wavy margins. Lower leaflets are long and tapered at both ends. Upper leaflets have little or no tapering toward the leaf stalk. Sterile leaves have a prominent network of veins, and are sparsely covered with white hairs on the underside. FERTILE LEAVES are shorter (approximately 1 foot tall) than sterile leaves, and are composed of numerous, compact, upward-pointing leaflets. Each leaftlet, in turn, is composed of many hardened, beadlike subleaflets that become dark brown when mature.

  • Fruits and Seeds:

    Spore cases (spore-producing structures) are produced within the hardened, beadlike sections of the fertile leaflets, which become dark brown when mature. Spores are minute.

Biology:

Spores of sensitive fern are produced August through September. The sterile leaves of sensitive fern wither quickly with the first frost, leaving behind the stiff, beaded fertile leaves.

Toxicity:

Sensitive fern contains toxic compounds that have not yet been identified, and little is known regarding conditions of toxicity. Poisonings have been reported for horses consuming sensitive fern foliage.

Facts and Folklore:

  • The genus name, 'Onoclea', means 'closed vessel' in Greek, referring to the closed, beadlike subleaflets of the fertile leaves.

  • The species name, 'sensibilis', means 'sensitive', referring to how quickly the sterile leaves die back after the first frost.