We present a phylogenetic analysis of the Betulaceae including at least one species of each subgeneric division (26 taxa) of the six genera (Betula, Alnus, Carpinus, Corylus, Ostrya, Ostryopsis). Parsimony analyses based on ribosomal DNA sequences of 5S gene spacers and ITS support the monophyly of the subfamilies and all genera. Likelihood ratio tests show rate heterogeneity across lineages, and therefore we made the phylogenetic trees ultra-metric by transforming ML and MP branch lengths (HKY85 + gamma model of DNA evolution) using the non-parametric rate smoothing method of Sanderson. We estimated divergence times within the family using one of the six most parsimonious trees and six calibration points from the extensive fossil record of Betulaceae. Five of these fossils are from extant members of the family, one of each genus except Ostryopsis, which is not represented in the fossil record. The sixth fossil is the extinct Alnus-type pollen Alnipollenites from the Santonian. The presence of arci in Alnipollenites is characteristic of genus Alnus, thus making it the earliest evidence in the fossil record for Betulaceae. The calibration was performed using both the stem lineage and crown group nodes. The resulting estimates were compared to the fossil estimates and used collectively to determine the most appropriate position for the fossils. Using methods developed by Marshall, the confidence interval of the stratigraphic range of Alnus was assessed using the well-documented palynological record of the genus and its relatives such as Alnipollenites. The results of these confidence interval evaluations were compared to the molecular estimates.

Key words: Betulaceae, calibration, confidence intervals, fossils, NPRS, nrDNA