What is the toughest timber flooring?

Timber hardness is be measured by the Janka hardness test.
The test measures the force required to push a steel ball with a diameter of 11.28mm into the wood to a depth of half the ball’s diameter.
In Australia the most commonly reported measure is quoted in kilo newtons (kN), where 1kN = 100kg, and the most common use of the Janka hardness rating is to determine whether a species is suitable for use as a flooring timber. The higher the number the harder the species is, therefore the Janka hardness test is ideal for determining how a floor will resist dents and wear.
A hardness in excess of 5.0kN is generally considered suitable for use as a flooring timber.
Timber Janka ratings range from Tasmanian Oak at 5.5(kN) up to 15.8(kN) for Strand Woven Bamboo.