Ilex paraguariensis begins as a shrub and then matures to a tree, growing up to 15 metres (49 ft) tall. The leaves are evergreen, 7–110 millimetres (0.3–4.3 in) long and 30–55 millimetres (1.2–2.2 in) wide, with serrated margins. 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 related xanthine alkaloids, and are harvested commercially.
Yerba mate contains three xanthines: caffeine, theobromine, and theophylline, the main one being caffeine. Caffeine content varies between 0.7% and 1.7% of dry weight (compared with 0.4–9.3% for tea leaves, 2.5–7.6% in guarana, and up to 3.2% for ground coffee).