betulin

 a term originally applied to a substance obtained as a resin or tar by extraction from the outer bark of the common European white birch (Betula alba); now referring to the chemical compound (C30H50O2) having a cyclopentanophenanthrene ring system, which is the main constituent of that extract, and which may be obtained crystalline; -- called also birch camphor.  Watts.  [1913 Webster]