Ancient or recent? Insights into the temporal evolution of the Bruniaceae

The Bruniaceae are a South African plant family endemic to the Cape Floristic Region with one geographic outlier (Raspalia trigyna) in the Natal Province. Recent molecular phylogenetic analyses have cast new light upon inter- and intra-generic relationships within the family. The present work uses those data to gain insights into the temporal evolution of Bruniaceae by inferring a molecular clock. For calibration, the inferred age of Berzelia cordifolia (3–5 My) was used, based on its distribution restricted to the geologically young limestone area around Bredasdorp. The results are consistent with the purported Cretaceous age of the family (‘palaeoendemics’), but also suggest that most extant species are relatively young. The major diversification of the family may have happened within relatively recent times (between 18 and 3 Mya), simultaneously with the establishment of the present Mediterranean climate in their environment. The disjunct distribution of Raspalia trigyna may be attributable to migration over sandstone exposed during a brief marine regression of the Indian Ocean at the Miocene–Pliocene boundary.