Sensitive fern is common in temperate regions of Asia and North America.
Its common and species names reflects the fact that its fronds give out at the first sign of frost (though its roots
remain intact for next spring). Onoclea, from Greek meaning “closed vessel,”
refers to the closely rolled fertile fronds. This genus has only a single species.
Identification: This robust fern favors wet areas,
where its roots put up irregular rows of erect or tilted fronds. Young stems are red, and the
emerging “fiddleheads” are pale red. Sterile
fronds are 8-40" (20-101 cm) long, with 8-12 pairs of opposing light green pinnae (leaflets).
Fertile fronds are 10-20" (25-50 cm) long, composed of pinnae so tightly rolled up as
to resemble beads—the sori are inside the rolled leaves. The “beads” are ¹/₁₆-⅛" (2-4 mm)
In winter, the sterile fronds die back and disappear, but the fertile fronds,
now dark brown and hard, remain as an unmistakable sign of this species.
Onoclea sensibilis on Earl J.S. Rook's Flora, Fauna, Earth, and Sky ...
The Natural History of the Northwoods