From The Collaborative International Dictionary of English v.0.48 :
Sagebrush \Sage"brush`\, n. A low irregular shrub ({Artemisia tridentata), of the order Compositae, covering vast tracts of the dry alkaline regions of the American plains; -- called also sagebush, and wild sage. [1913 Webster]From WordNet (r) 3.0 (2006) :
sagebrush n 1: any of several North American composite subshrubs of the genera Artemis or Seriphidium [syn: sagebrush, sage brush]