Plant adaptation to serpentine soil has been a topic of study for many decades, yet investigation of the genetic component of this adaptation
has only recently begun. We review the defining properties of
serpentine soil and the pioneering work leading to three established
physiological and evolutionary mechanisms hypothesized to be
responsible for serpentine tolerance: tolerance of a low
calcium-to-magnesium ratio, avoidance of Mg toxicity, or a high Mg
requirement. In addition, we review recent work in serpentine ecology
documenting the high proportion of endemic species present, the
adaptive morphologies of serpentine-tolerant plants, and the
distinctive structure of serpentine communities. Studies of the
physiological mechanisms proposed to confer serpentine tolerance have
shown that uptake of particular ions and heavy metals varies between
serpentine-tolerant and -intolerant species. Recent studies examining
the genetic basis of serpentine adaptation have shown
serpentine-adaptive quantitative trait loci (QTL) to have large
phenotypic effects, drought tolerance to be as important as metal
tolerance, and serpentine adaptation to have evolved independently
multiple times within species. Investigations of plant races and
species adapted to contrasting soil types have shown disparate
flowering times, divergent floral morphologies, and pollen
incompatibility to contribute to reproductive isolation. Finally, we
propose that future studies involving serpentine systems should merge
the fields of ecology, evolution, physiology, and genetics.