What is the toughest tree?

The heaviest and the hardest wood in the world is Snakewood (Piratinera guianensis).

There are also many other candidats to be the hardest wood: ironwood, huacapu and some types of eucalypts.

You can find a list of the hardest and the softest woods at the link in the Related Links. You will find a list that has been compiled according to the JANKA HARDNESS TEST.