The ombú (phytolacca dioica) is a large, rapidly growing, herbaceous evergreen tree of the pampas of Argentina and Uruguay, in South America. Indeed, it is the only tree native to the pampas, though it is more of a huge bush.

It has a broad trunk (up to 15m in girth) with a high water content, and dark green elliptical leaves, sometimes boiled in water and used as a laxative. The bark is thick, the wood soft and spongy, and the sap poisonous.

The word "ombú" is from the Guaraní word, "shadow".