South Africa’s distinctive flag symbolizes its diverse cultural heritage. The nation’s biological heritage is no less impressive: whereas the British Isles is home to about 1,500 plant species, South Africa’s Cape region houses more than 9,000 in one-third of the area, with perhaps the highest concentration of endangered plant species anywhere in the world1. On page 757 of this issue, Forest et al.2 report how an evolutionary approach to plant conservation might lead to surprising choices among conservation areas. The study brings the concept of what might be called evolutionary heritage into sharp focus. The species is the fundamental unit of biodiversity, and so the most common conservation approach is to concentrate resources in the most species-rich areas. This assumes that all species are equivalent, but species vary dramatically in their evolutionary isolation3. Most have many and similar brethren (there are 3,400 members of the rose family, for instance), whereas some have only distant relatives (the evergreen shrub Amborella trichopoda seems to have no close relative among the entire ensemble of flowering plants). Biodiversity is not just the number of species but also the differences between them (Fig. 1, overleaf), and it seems intuitively obvious that both number and difference should inform conservation decisions4. Indeed, algorithms that select areas to maximize the evolutionary divergence among species in a particular region are several decades old5.
