The Collaborative International Dictionary of English v.0.48:

brittlebush \brittlebush\ n.
   1. fragrant rounded shrub of SW US and adjacent Mexico having
      brittle stems and small crowded blue-green leaves and
      yellow flowers; produces a resin used in incense and
      varnish and in folk medicine.

   Syn: brittle bush, incienso, Encelia farinosa.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

brittlebush
    n 1: fragrant rounded shrub of southwestern United States and
         adjacent Mexico having brittle stems and small crowded
         blue-green leaves and yellow flowers; produces a resin used
         in incense and varnish and in folk medicine [syn:
         brittlebush, brittle bush, incienso, Encelia
         farinosa]