Onoclea sensibilis

Sensitive Fern

Onoclea sensibilis, Sensitive Fern, Photo © by Earl J.S. Rook
Sensitive Fern
Photo © by Earl J.S. Rook

Flora, fauna, earth, and sky...
The natural history of the northwoods


Name:

  • Onoclea, from the Greek onos (onos), "vessel," and kleio (kleio), "to close", referring to the closely rolled fertile fronds.
  • sensibilis, from the Latin, "sensitive"
  • Common Name, from the observation of early settlers that it was very sensitive to frost, the fronds dying quickly when first touched by frost.
  • Other common names include Bead Fern, Meadow Brake, Onoclée Sensible (Qué)

Taxonomy:

  • Kingdom Plantae, the Plants
    • Division Polypodiophyta, the True Ferns
      • Class Filicopsida
        • Order Polypodiales
          • Family Dryopteridaceae
            • Genus Onoclea
  • Taxonomic Serial Number: 17636
  • Also known as Angiopteris sensibilis, Calypterium sensibile, Onoclea augescens, Onoclea interrupta, Onoclea obtusilobata, Ragiopteris obtusilobata, Ragiopteris onocleoides, Riedlea sensibilis

Description:

  • A , , ¾, º, é
  • A deciduous, coarse textured, perennial fern, with broader leaves and pinnae (leaflets) than most other North Country ferns; 18"-24" tall.
  • Sterile Fronds light green, leathery, broad, and almost triangular, typically tilted up and back.
    • Petiole (leaf stalk) brittle, smooth, and usually longer than blade with a shallow furrow in front; yellow/pale tan, and dark brown at base with a few scales.
    • Blade of 8-12 pairs of nearly opposite leaflets with wavy margins, prominent network of veins, and sparse white hairs on underside.
    • Rachis (axis) winged, more broadly toward tip.
    • Pinnae (primary leaflets) lanceolate to oblong, with or without teeth or with a few undulations. Lower leaflets long and tapered at both ends; upper leaflets with little or no tapering toward rachis.
    • Pinnules (secondary leaflets) blades mostly 4"-12" long, 4"-14" wide, with 8-12 pairs of opposite pinnae, these sinuate to pinnatifid, ½"-1¼" wide, sparsely white-hairy on the veins beneath; petioles shorter to about as long as the blade.Sterile leaves yellow-green, deltate, coarsely divided, 5"-13½" × 6"-12". Petiole of sterile leaf black, 22--58 cm, flattened at base; rachis winged, becoming broader toward apex. Pinnae 5--11 per side, lanceolate; proximal pinnae 9--18 cm, margins entire, sinuate, or laciniate.
  • Fertile Fronds brown, shorter than sterile leaves (approximately 1' tall), and structurally unlike the green sterile fronds. Fertile fronds produced Aug--Sep, often persistent into the following year.
    • Petiole (leaf stalk)Petiole 19--40 cm, base sparsely scaly.
    • Blade
    • Rachis (axis)
    • Pinnae (primary leaflets) numerous, compact, upward-pointingPinnae linear, 5--11 per side, 2.5--5 cm; pinnae strongly ascending, 2-5 cm long, Sporophyll leaves green, becoming black at maturity, oblong, 7--17 × 1--4 cm.
    • Pinnules (secondary leaflets) many hardened, beadlike subleaflets that become dark brown when mature. ultimate segments revolute to form beadlike structures, 2--4 mm diam.divided into bead-like pinnules with inrolled margins enclosing the sori, the pinnules 3-4 mm wide, becoming dry, hard, eventually separating to release the spores;
    • Sensitive fern is easily killed with the first frost, leaving behind the stiff, beaded fertile stalks. blade pinnate-pinnatifid, mostly 5-15 cm long;
  • Root System of creeping rhizomes 4mm-7mm thick, growing near the soil surface; stout, brown, smooth, and extensively branched and spreading. Numerous roots grow along the rhizomes and produce a fibrous mat.
  • Fiddleheads The curled leaves (fiddleheads) emerging from rhizomes form a distinctive, pale red mass in the spring
  • Fruit spore cases produced within the hardened, beadlike sections of the fertile leaflets, becoming dark brown at maturity. sori globose, covered by a delicate, hoodlike indusium.
    • Sori clustered like beads or grapes on the upright fertile fronds
    • Spores minute, on separate fertile fronds, within bead-like modified leaflets
  • Leaf forms with pinnae intermediate between those of sporophylls and sterile leaves, or with pinnae fertile only on one side of the blade, can occur on plants that also bear normal leaf forms.
  • As with Matteuccia struthiopteris, sporophylls of Onoclea sensibilis persist through the winter and release the green spores in spring before the sterile leaves expand.

Identification:

  • Identifiable as
  • Distinguished from
  • Field Marks
    • large, deeply pinnatifid fronds
    • spherical spore-bearing bodies borne on a separate stalk

Distribution:

  • Manitoba to Newfoundland, south to Texas, the Gulf Coast, and Florida
  • Also, East Asia
  • Naturalized in western Europe

Habitat:

  • Wet meadows, thickets, and woods; stream and riverbanks; swamps and bogs; usually in slightly acidic soil.
  • In sunny or shaded locations, often forming thick stands; uncommon in forested environments.

Fire:

Associates:

History:

Uses:

  • Implicated in the poisoning and death of horses grazing low, wet areas.

Reproduction:

  • Reproduces by spores and vegetatively by rhizomes

Propagation:

  • By spores or rhizome division in spring.

Cultivation:

  • A low maintenance fern for moist sites which, despite its name, tolerates the toughest of conditions.
  • Hardy to USDA Zone 3 (average minimum annual temperature -40ºF)
  • Cultural Requirements
    • Shade or part shade; will tolerate sun with adequate moisture
    • Average garden soil, on the acidic side
    • Moisture: moist soil; will tolerate wet soils and can be used near water.
    • Fertilization unnecessary
  • Size 18"-24"W x 12"-24"H
  • Good for bogs, natural gardens, woodland drifts, shade groundcover
  • Available by mail order from specialty suppliers or at local nurseries
  • Spreads to form colonies; can become weedy and invasive
  • Winter survival improves if dried fronds are left on plant over winter.

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Last Updated on 26 February, 2004