Middle Miocene (Seldovian)
Sucker Creek Formation – Sucker Creek Flora
Malheur County, Oregon, USA
Two 20mm acorns on 67mm slab.

Plant. Seed.

Quercus is the genus that includes oak trees.  The earliest confidently-known fossils are pollen from the Late Paleocene of Austria, and by the Middle Eocene, Quercus is already known from North America, Europe, and Asia.  While oaks originated in tropical forests, they thrived as climates became drier and cooler as a general trend across the Oligocene and Miocene while other trees retreated to lower latitudes.  Many modern species may have appeared around the time these acorns were buried.

From tiny acorns mighty oaks grow.
– 14th century Old English proverb