PORTER, J. MARK* AND LEIGH A. JOHNSON. Rancho Santa Ana Botanic Garden, 1500 North College Avenue, Claremont, CA 91711. Botany and Range Science, 451 WIDB, Brigham Young University, Provo, UT 84602. - Age and diversification and their implications for historical biogeography of Polemoniaceae.
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