Eocene Age 54 million years ago

A rare twig bearing both leaves and fruits serves as a Rosetta stone, linking the vegetative and reproductive structures that formerly were only known from dispersed organs. Fruit and foliage characters distinguish Populus Tidwellii sp. n. from Populus cinnamomoides (Lesquereux) MacGinitie (typified on specimens from Green River Station, WY), to which the isolated leaves had formerly been attributed. In addition, new data from fruits and foliage confirm that there were two distinct sympatric species of Populus in the Parachute Creek flora. These species, together with Pseudosalix and Salix, provide our earliest record of diverse Salicaceae. An interesting feature of P. tidwellii is that the inflorescence is terminal in contrast to extant species of Populus, in which the catkins are axillary and borne on the wood of the previous season. In addition, the infructescence shows lateral branching near its base, distinguishing it from the simple racemes of extant species of the genus.

While the Green River Formation is a Lagerstätte most known for its exquisite fish fossils, the fossil flora and fauna are truly diverse, including plants, invertebrates, and vertebrates (including reptiles, mammals) with even Eocene stromatolites represented. This willow leaf shows nice venation. There is also a tiny insect, not so well preserved. Insects are not commonly seen in Green River fossils.