Sensitive fern
General poisoning notes:
Sensitive fern (Onoclea sensibilis) is a native plant that is found through eastern Canada into Manitoba. The plant, often abundant in low, wet areas, has been implicated in the poisoning and death of horses in field cases. Only one set of experimental poisonings has been undertaken, but the resulting symptoms were similar when horses were fed hay containing sensitive fern (Waller et al. 1944).
Description
Leaves irregularly spaced along stem. Sterile leaves yellow-green, deltate, coarsely divided, 13--34 × 15--30 cm. 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. Sporophyll leaves green, becoming black at maturity, oblong, 7--17 × 1--4 cm. Petiole 19--40 cm, base sparsely scaly. Pinnae linear, 5--11 per side, 2.5--5 cm; ultimate segments revolute to form beadlike structures, 2--4 mm diam. Sori borne on free veins, enclosed by ultimate segments. 2 n = 74.
Nomenclature:
Scientific Name: Onoclea sensibilis L.
Vernacular name(s): sensitive fern
Scientific family name: Polypodiaceae
Vernacular family name: frern
Onoclea sensibilis L.
Geographic Information
Labrador, Manitoba, New Brunswick, Nova Scotia, Ontario, Prince Edward Island, Quebec.
Notes on Poisonous plant parts:
When the fronds (aboveground leaves) are included in hay, they produce toxic symptoms in horses. The fertile fronds (spore-bearing stalks) are also included in hay. A literature search did not reveal any reports on the toxin, nor was the plant organ that contains the toxin identified.
Toxic parts:
Leaves.
Toxic plant chemicals:
Unknown chemical.
Animals/Human Poisoning:
Note: When an animal is listed without additional information, the literature (as of 1993) contained no detailed explanation.
Horses
General symptoms of poisoning:
brain, congestion of
colic
death
falling down
gait, unsteady
icterus
incoordination.
Notes on poisoning:
Ingesting hay containing sensitive fern produces the following symptoms: difficulty in eating, falling down, walking as if blind, rubbing against objects, and death. Postmortem examination showed extreme icterus, swollen liver, paralysis of the alimentary tract, and brain edema. Old horses are more affected than younger ones. Horses that are worked and are fed a grain supplement, in addition to hay that includes the fern, are not affected. Recovery may occur if the horses are given good hay and grain before serious nervous symptoms develop Waller et al. 1944).
