Adaptation and divergence in edaphic specialists and generalists: serpentine soil endemics in the California flora occur in barer serpentine habitats with lower soil calcium levels than serpentine tolerators.

These results suggest serpentine endemism is associated with adaptation to chemically harsher and more bare serpentine habitats. It may be that this adaptation trades off with competitive ability, which would support the longstanding, but rarely tested, competitive trade-off hypothesis.