Toxic Parts:
Flower Color:
  • flower color
waterside, meadows, woodlands

Time of Greatest Risk


Geographical Distribution

Horsetail distribution - United States


Equisetum spp

Canuela, Monkey Grass, Snake Grass, Scouring Rush
6/ 10
Horsetails are perennial, non-flowering, erect plants which are composed of more than 30 species in the genus, belonging to the Equisetaceae family. This fern-like, spore-producing plant is generally found in moist-to-wet areas across Europe and North America. It is also sometimes a contaminate in hay.

Horsetail Toxic Components

The plant contains several toxic compounds, but its toxicity is believed to be due to the presence of the enzyme thiaminase, the alkaloid nicotine and piperidine alkaloids. Thiaminase is an enzyme that destroys thiamine, an important B vitamin that is needed for proper brain function.

Symptoms of poisoning in horses develop slowly, and begin with unthrifty appearance, weight loss without loss in appetite, diarrhea, and slight incoordination. Without treatment, signs will progress to more extreme--leading to balance problems and loss of control of muscle movement, eventually leading to death in approximately 1-2 weeks.