A small monophyletic family of approximately 360 species, Polemoniaceae are most diverse in the New World. Historical discussions of diversification of this family have relied upon (1) classification as recapitulating phylogeny and (2) major lineages of the family corresponding roughly to Arcto-tertiary or Madro-tertiary elements. The combination of quantitative phylogenetic (maximum likelihood) methodologies and new fossil evidence provide a framework to test these hypotheses of diversification. Phylogenetic estimates, based on chloroplast (matK, trnL-F) and nuclear (nrITS) DNA sequences, while supporting some relationships suggested by recent classification, refute the implied pattern of diversification. Molecular clock estimates, using the three genic regions and the fossil Gilisenium hueberi as a calibration point, infer that nearly all of the diversification, resulting in present day genera, occurred during the mid-Tertiary (58-35 MYBP). Indeed, the common ancestor of the so-called "temperate group" may date to 100 MYBP or earlier, during the Cretaceous. We further show that present day distributions and ecological preferences may be misleading in their implications for historical origins of lineages within Polemoniaceae.

Key words: historical biogeography, molecular clock, Polemoniaceae