The oldestPinusand its preservation by fire

Abstract

Pinus (Pinaceae) is a diverse conifer genus that dominates Northern Hemisphere forests today and is noteworthy for its fire-adapted traits. Here we describe the oldest known fossils attributable to the genus from the Lower Cretaceous (Valanginian, ca. 133–140 Ma) part of the Chaswood Formation of Nova Scotia, Canada. Pinus mundayi sp. nov. comprises charred long-shoots, which show a constellation of derived characters including (1) axial resin ducts with thin-walled epithelial cells in the secondary xylem and phloem, (2) fenestriform or pinoid cross-field pits, and (3) helically arranged short-shoots that pass through growth ring boundaries before distally diverging into two separate needle bases. The fossils, which are interpreted as remains of an evergreen two-needle pine, provide a new constraint on timetrees of Pinaceae evolution. Their preservation as charcoal and the occurrence of resin ducts, which produce flammable terpenes in modern pines, show that Pinus has co-occurred with fire since its Mesozoic origin.