Onoclea sensibilis Linnaeus

Sensitive fern, bead fern

Etymology Sensibilis means sensitive; responds quickly by wilting on picking the fronds, or maybe to frost susceptibility.
Description Rhizome: long-creeping, 4mm-7mm thick, growing near the soil surface; stout, brown, smooth, and extensively spreading, producing a fibrous mat.
Frond: 60 cm high by 30 cm wide, sterile deciduous; fertile persistent, dimorphic, blade/stipe ratio: 1:1.
Stipe: inflated base (tropophod), dark brown at base, a few light-brown scales, deciduous, vascular bundles: 2, elongate.
Blade: sterile blades, 1-pinnate-pinnatifid at base, less upward, triangular, papery, linear to lanceolate scales and/or multicellular hairs.
Pinnae: 5 to 11 pair, lowest pinnae largest or nearly so, stemless or attached laterally to the rachis; pinnules fertile ones roll up into bead-like segments, enclosing the sporangia; costae flat above; margins entire to sinuate; veins sterile: netted, fertile:free.
Sori: round, covered by rolled-up margins, indusium: vestigial, not seen, sporangia: green, the enveloping fertile pinnules becoming black in maturity; spores are green in maturity, maturity: winter.
Culture Habitat: swamps, thickets, marshes, or low woods, in sunny or shaded locations, often forming thick stands. Distribution: eastern North America, eastern Asia. Hardy to -40C, USDA Zone 2.
Distinctive Characteristics Separated from Woodwardia areolata by entire margins here and finely serrate margins there, by pinnatifid pinnae here and simple pinnae there, and by very different fertile pinnae. Once seen, never forgotten. Onoclea sensibilis has a reputation for aggressiveness.
Onoclea sensibilis
Onoclea sensibilis. Left to right, fertile, sterile fronds, rhizome.  Illustration by Edgar Paulton, from How to Know the Ferns and Fern Allies, John T. Mickel, 1979 Wm. C. Brown Co.
Onoclea sensibilis
Onoclea sensibilis. Two elongated vascular bundles at 90 at the stipe base, uniting upwards at the back, forming an inverted u-shape.  Drawing from Ferns of Northeastern United States, Farida A. Wiley, 1936.

Onoclea sensibilis. Sterile frond: 1-pinnate-pinnatifid at base, pinnatifid above.  Web pages of the Connecticut Botanical Society, with permission.
Onoclea sensibilis
Onoclea sensibilis.rhizome  Robbin Moran
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