The Collaborative International Dictionary of English v.0.48:

Queensland nut \Queens"land nut`\ (Bot.)
   The nut of an Australian tree (Macadamia ternifolia). It is
   about an inch in diameter, and contains a single round edible
   seed, or sometimes two hemispherical seeds. So called from
   Queensland in Australia.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Queensland nut
    n 1: bushy tree with pink to purple flowers [syn: Queensland
         nut, Macadamia tetraphylla]