Fossil Sumac Leaf | Rhus longipetiolata | Green River Formation | Wyoming

Rhus longipetiolata (Sumac leaf)
Eocene (51.98 Million Years Ago)
Green River Formation, Wyoming, USA
In Stone Fossils Private Quarry

Plate approx. size: 6.75" x 4.5"

Leaf approx. size: 2"

This beautifully preserved fossil represents an ancient sumac leaf, Rhus longipetiolata, a member of the Anacardiaceae family (the same family as modern sumacs, cashews, and mangoes). The species is named for its distinctive long, slender petiole (leaf stem), which sets it apart from other fossil sumacs of the Green River Formation.

The leaf typically shows fine serrated margins, a strong central midrib, and delicate branching veins that create a network across the surface. These features are often visible in detail thanks to the exceptional preservation of Fossil Lake sediments.

During the Eocene, this plant grew as a shrub or small tree along the lake margins in a warm, subtropical environment. Like modern sumacs, it likely formed thickets and contributed to the diversity of the ancient Green River ecosystem.

Owning a specimen of Rhus longipetiolata offers not only a glimpse of the Eocene world but also a direct connection to a lineage of plants that still thrive today.