The Collaborative International Dictionary of English v.0.48:
Sneezeweed \Sneeze"weed`\, n. (Bot.) A yellow-flowered composite plant (Helenium autumnale) the odor of which is said to cause sneezing. [1913 Webster]WordNet (r) 3.0 (2006):
Helenium autumnale n 1: North American perennial with bright yellow late summer flowers [syn: autumn sneezeweed, Helenium autumnale]