Eocene Green River Rhus P-GRP2-16-018Rhus cf. longipetiolata Green River Formation Middle Eocene Lincoln County, Wyoming This specimen is very nice representative of the Sumac Rhus. The leaf is 7. 5 cm long and is well preserved. Rhus are a relatively common element in the Green River flora. There are as many as 250 living species in the genus Rhus. They live in subtropical and temperate climates and occur as shrubs or small trees.