gumweed(n = noun.plant) gum plant, rosinweed, tarweed - any of various western American plants of the genus Grindelia having resinous leaves and stems formerly used medicinally; often poisonous to livestock;
any of various Western American plants of the genus Grindelia having resinous leaves and stems formerly used medicinally; often poisonous to livestock. [WordNet 1.5]