The aim of this study was to determine the evolutionary time line for rust fungi and date
key speciation events using a molecular clock. Evidence is provided that supports a contemporary
view for a recent origin of rust fungi, with a common ancestor on a flowering plant.
Divergence times for > 20 genera of rust fungi were studied with Bayesian evolutionary
analyses. A relaxed molecular clock was applied to ribosomal and mitochondrial genes, calibrated
against estimated divergence times for the hosts of rust fungi, such as Acacia
(Fabaceae), angiosperms and the cupressophytes.
Results showed that rust fungi shared a most recent common ancestor with a mean age
between 113 and 115 million yr. This dates rust fungi to the Cretaceous period, which is much
younger than previous estimations. Host jumps, whether taxonomically large or between host
genera in the same family, most probably shaped the diversity of rust genera. Likewise,
species diversified by host shifts (through coevolution) or via subsequent host jumps. This is in
contrast to strict coevolution with their hosts.
Puccinia psidii was recovered in Sphaerophragmiaceae, a family distinct from Raveneliaceae,
which were regarded as confamilial in previous studies.