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®

sneezeweed
     n : any of various plants of the genus Helenium
         characteristically causing sneezing