PINUS BAILEYI AND ITS BEARING ON THE HISTORY OF HARD PINES (SYLVESTRES) IN THE PALEOGENE OF WESTERN NORTH AMERICA

Pinaceae were major components in Paleogene paleofloras of western North America (WNA), with Pinus being well represented in upland floras. Molecular and morphological phylogenies of the genus Pinus have been helpful in recognizing monophyly of the two subgenera, Pinus (hard pines) and Strobus (soft pines), as well as a number of sections and subsections. However, whether subgenus Pinus or Strobus is derived still remains unresolved. Based on the earliest megafossil record of the genus, P. belgica from the early Cretaceous of Western Europe suggests the hard pines are the least specialized and Western Europe a potential site of origin, with subsequent east-west dispersal throughout Eurasia and into North America. Records of Cretaceous Pinus pollen are somewhat less certain since Pityostrobus and other pine-like taxa likely produced pollen morphologically similar to Pinus. Reexamination of P. baileyi from upland Eocene and Oligocene sites (45-~31 Ma) in Idaho shows it is an excentromucronate hard pine (not a soft pine related to the WNA subalpine “foxtail pines” of Balfourianae), with close resemblance to those of subsection Halepenses and Sylvestres showing most similarity to the tropical/temperate Asian species, P. kesiya and P. massoniana. Today, all extant Sylvestres have a Eurasian distribution, except P. resinosa of northeastern United States and Canada and the Cuban P. tropicalis. However, neither molecular nor morphological studies have settled the debate over the relationship of these two species and their inclusion in Sylvestres. Pinus baileyi is also similar to P. resinosa, but primarily differs in having a mucronate umbo and therefore at least raises questions regarding its relationship, if any, to P. resinosa and P. tropicalis. Pinus baileyi extends the stratigraphic and geographic range of Sylvestres-type pines in WNA and adds to a record previously known only from four species of permineralized cones, wood, seeds, and fascicles from the Eocene of British Columbia and Washington. Moreover, it provides an opportunity to review the Sylvestres megafossil record in light of current phylogenetic and biogeographical hypotheses for the subsection Sylvestres.