Tar·weed n. Bot. A name given to several resinous-glandular composite plants of California, esp. to the species of Grindelia, Hemizonia, and Madia.
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  tarweed
       n 1: any of various resinous glandular plants of the genus Madia;
            of western North and South America
       2: any of various western American plants of the genus
          Grindelia having resinous leaves and stems formerly used
          medicinally; often poisonous to livestock [syn: gumweed,
           gum plant, rosinweed]