Pinus Pollen Cones from the Middle Eocene Princeton Chert (Allenby Formation) of British Columbia, Canada

Abstract

Anatomically preserved pollen cones are described from the Middle Eocene Princeton chert of British Columbia, Canada. Cones are ellipsoidal; range from 2.8 to 6.9 mm in length, 1.6 to 3.5 mm in diameter; and are often subtended by scale leaves. Cone axes contain longitudinally oriented, cortical resin canals and 14-18 vascular bundles. Microsporophylls are helically arranged, each bearing two abaxial pollen sacs, many containing pollen grains. Grains are bisaccate and monosulcate, ranging from 50 to 70 μm in length and 27 to 43 μm in width. Proximally, the corpus is rugulate with a tectate-alveolate infrastructure. Sacci have a well-defined endoreticulum and an external ornamentation that is psilate to scabrate. Variations in cone size, cone anatomy, and pollen morphology indicate that several developmental stages are preserved. The large number of cones present in the chert, especially those representing short-lived ontogenetic stages, and the preservational quality of the cones support depositional interpretations for a rapid burial and preservation. These factors also indicate that the pollen cone-producing plants occupied a marginal position in proximity to the lacustrine environment. Four species of Pinus, based on woody twigs, dwarf shoots, leaves, and ovulate cones, are presently known from the Princeton chert. The association of these pollen cones with Pinus similkameenensis leaves and Pinus arnoldii ovulate cones indicates possible taxonomic affinities among these species. The Princeton chert specimens are the oldest Pinus pollen cones to be described and are the first in the genus for which fossil pollen ultrastructure has been described.