Levyns’ Law: explaining the evolution of a remarkable longitudinal gradient in Cape plant diversity

It has been known for many decades that the diversity of clades endemic to the Greater Cape Floristic Region (GCFR) declines along a longitudinal (west-east) gradient, in concert with a reduction in the proportion of winter rainfall. In honour of the pioneering work by Margaret Levyns, we recognise this pattern as Levyns’ Law, and illustrate it with distribution data for 23 speciose endemic clades. All patterns were consistent with Levyns’ Law....