Yerba mate, Ilex paraguariensis, begins as a shrub and then matures to a tree and can grow up to 15 metres (49 ft) tall. The leaves are evergreen, 7–11 cm long and 3–5.5 cm wide, with a serrated margin. The leaves are often called yerba (Spanish) or erva (Portuguese), both of which mean "herb". They contain caffeine (known in some parts of the world as mateine) and also contains related xanthine alkaloids and are harvested commercially.
The flowers are small, greenish-white, with four petals. The fruit is a red drupe 4–6 mm in diameter.