- Distinguishing features
- Native perennial herb with black horizontal rhizomes deep in the soil (often below plow depth), by means of which it spreads and forms large patches; leaves 3-4 feet tall in good sites; leaf stalk forks into three main parts, producing a triangular, bipinnately pinnatifid blade; spores produced in late summer in sporangia protected by the rolled-under edges of the blade.
- Deciduous fern with a horizontal root system that can grow up to several meters long.
- Geographic range
- Found throughout the United States in dry open woodlands. Spreads rapidly due to its extensive root system.
- Toxic principle
- Thiaminase splits the essential vitamin thiamine (B1) into its two inactive components, pyrimidine and thiazole, causing thiamine deficiency.
- Bracken fern is associated with poisoning of cattle, sheep, pigs, horses, and humans. Horses must consume a diet of 3-5% bracken fern for at least 30 days before clinical signs appear. Rhizomes are the most toxic portion of the plant.
- Mechanism of toxicologic damage
- Thiamine is essential in energy metabolism and is broken down by thiaminase. Thiamine deficiency causes CNS depression and polioencephalomalacia.
- Clinical signs
- Depression, muscle tremors, uncoordinated gait. Retinal degeneration and blindness. Hemorrhaging and bone marrow destruction, urinary bladder cancer, and digestive tract cancers.
- Laboratory Diagnosis
- Severe anemia may be seen. Decreased thiamine levels and increased pyruvic acid levels are seen.
- Treat horses with 5 mg/kg body weight of thiamine intravenously. Repeat the dose intramuscularly for several days. Nursing care and systemic antibiotics are also helpful.
- Feed animals a balanced diet free of bracken fern.
Read more in the Poisonous Plants of Pennsylvania Publication