The Collaborative International Dictionary of English v.0.48:

Ironbark \I"ron*bark`\, Ironbark tree \I"ron*bark` tree`\ (Bot.)
   The Australian Eucalyptus Sideroxylon, used largely by
   carpenters and shipbuilders; -- called also ironwood. Also
   applied to other Australian eucalyptuses with a hard, solid
   bark
   [1913 Webster +PJC]

The Collaborative International Dictionary of English v.0.48:

Ironwood \I"ron*wood`\, n. (Bot.)
   A tree unusually hard, strong, or heavy wood.
   [1913 Webster]

   Note: In the United States, the hornbeam and the hop hornbeam
         are so called; also the Olneya Tesota, a small tree
         of Arizona; in the West Indies, the Erythroxylon
         areolatum, and several other unrelated trees; in
         China, the Metrosideros vera; in India, the Mesua
         ferrea, and two species of Inga; in Australia, the
         Eucalyptus Sideroxylon, and in many countries,
         species of Sideroxylon and Diospyros, and many
         other trees.
         [1913 Webster]