WordNet (r) 3.0 (2006):

beefsteak morel
    n 1: a poisonous gyromitra; the surface of the fertile body is
         smooth at first and becomes progressively undulating and
         wrinkled (but never truly pitted); color varies from dull
         yellow to brown [syn: Gyromitra esculenta, brain
         mushroom, beefsteak morel]