Areas of high species richness, particularly those with high numbers of species unique to that area, seem obvious candidates for conservation action. But this takes little account of the evolutionary potential of the plants and animals [living in] that ecosystem. With the likelihood of rapid global change high, the conservation of evolutionary processes is increasingly recognized as a priority.
They go on to describe a genomic study of the flora in South Africa's Cape Province--widely recognized as a "biodiversity hotspot". They examined the length of evolutionary pathways connecting given sets of taxa.
The scientists argue that plants from the more diversity-rich western Cape actually have less potential to evolve than plants from the less diversity-rich eastern Cape.