sneezewort

Sneezewort refers to a strong-scented, Eurasian perennial herb (Achillea ptarmica) that resembles yarrow but has simple leaves and large flower heads. It is also sometimes used to refer to white hellebore or sneezeweed.1

Sneezeweed, on the other hand, is a general term for several composite plants, most notably the North American perennial herb (Helenium autumnale) with yellow ray flowers. A specific variety, western sneezeweed (Helenium hoopesii), is a rank perennial herb found in the western U.S. that has yellow flowers and is poisonous to livestock, causing illness in sheep.23