The tepuis have all of these qualities.

The cliffs are effective isolation barriers.

The summit environment is extremely specific in its conditions — the combination of high rainfall, nutrient-poor soils, strong UV radiation at altitude, and temperature patterns different from both the highland savannas and the lowland forests is sufficiently distinctive that it drives unique evolutionary responses.

And the isolation has been operating for a period measured in millions of years, sufficient for genuine speciation (the complete divergence of populations into reproductively isolated species).

For animal groups, the endemism rates are comparable.