The Collaborative International Dictionary of English v.0.48:

boysenberry \boysenberry\ n.
   1. a cultivated hybrid bramble of California having large
      dark wine-red fruit with a raspberrylike flavor.
      [WordNet 1.5]

   2. a large raspberry-flavored bramble fruit; a cross between
      blackberries and raspberries.
      [WordNet 1.5]

WordNet (r) 3.0 (2006):

boysenberry
    n 1: cultivated hybrid bramble of California having large dark
         wine-red fruit with a flavor resembling raspberries [syn:
         boysenberry, boysenberry bush]
    2: large raspberry-flavored fruit; cross between blackberries
       and raspberries