Aerial stems develop from horizontal rhizomes, which are highly branched and perennial. Because the rhizomes can grow quite rapidly, Equisetum is often invasive. If livestock pastures are invaded by Equisetum, it can cause problems for farmers and ranchers, as the aerial stems of Equisetum are poisonous. Equisetum arvense, a species found in the United States and southern Canada, is especially toxic in dry hay. Horses, sheep, and cows are all susceptible to Equisetum poisoning. Symptoms include trembling, rapid pulse, weakness, excitability, diarrhea, staggering, and cold in the extremities. The
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