Petasites hybridus (L.)G.Gaertn., B.Mey. & Scherb. Asteraceae. Butterbur, Bog rhubarb. Distribution: Europe, NW Asia. Culpeper (1650) writes: “The roots are ... exceeding good in violent and pestilential fevers, they provoke the terms, expel poison, and kill worms.” Modern herbalists recommend it for a wide range of therapies, but it contains pyrrolizidine alkaloids, which are hepatotoxic and cause liver cancers. Nevertheless, in a trial aimed at reducing frequency of migraine attacks, a standardised commercial preparation was well tolerated, and was effective at higher doses, but placebo in this trial reduced migraines by over 50% in 49% of the patients (Neurology 2004