John,

Teak. True teak, tectona grandis, not the faux teak currently used in imported
"teak" items, is very rot-resistant.  There's a saying to the effect that "No
one has ever seen a piece of rotten teak." This is not far from the truth.

The wood is full of silica, and hence rapidly dulls tools.

John Ruth
Metuchen, NJ