The Collaborative International Dictionary of English v.0.48:

Wartweed \Wart"weed`\, n. (Bot.)
   Same as Wartwort.
   [1913 Webster]

WordNet (r) 3.0 (2006):

wartweed
    n 1: not unattractive European weed whose flowers turn toward
         the sun [syn: sun spurge, wartweed, wartwort,
         devil's milk, Euphorbia helioscopia]