Aquatic and Wetland Vascular Plants of the Northern Great Plains

4. Polypodiaceae, the Polypody Family

5. Onoclea L. -- Sensitive fern

1. Onoclea sensibilis L.

Rhizomes spreading and branching, 4-7 mm thick, the scales caducous. Fronds annual, erect, dimorphic, the fertile fronds brown, structurally unlike the green sterile fronds. Sterile fronds pinnate at the base, pinnatifid upward, the rachis broader-winged toward the tip; blades mostly 10-30 cm long, 10-35 cm wide, with 8-12 pairs of opposite pinnae, these sinuate to pinnatifid, 1-3 cm wide, sparsely white-hairy on the veins beneath, the veins anastomosing; petioles shorter to about as long as the blade. Fertile frond surpassed by the sterile ones; blade pinnate-pinnatifid, mostly 5-15 cm long; pinnae strongly ascending, 2-5 cm long, 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; sori globose, covered by a delicate, hoodlike indusium. Fertile fronds produced Aug--Sep, often persistent into the following year. Swampy woods, wet meadows and marshes, where water is fresh; scattered from e ND to NE, especially common in the Sand Hills; (Newf. to Man., s to FL and TX).


Onoclea sensibilis, a vegetative frond with pinnatifid divisions and an associated dark brown fertile frond, both arising from a rhizome.

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