Source : Webster's Revised Unabridged Dictionary (1913)

Sneezeweed \Sneeze"weed`\, n. (Bot.)
   A yellow-flowered composite plant ({Helenium autumnale}) the
   odor of which is said to cause sneezing.

Source : WordNet®

Helenium autumnale
     n : North American perennial with bright yellow late summer
         flowers flowers [syn: {autumn sneezeweed}]