Yerba maté is a large member of the evergreen oak family (Ilex paraguariensis). In its native S American forests it can grow up to 15 meters (45 feet) tall. However, in cultivation, it is usually hard-pruned at least once a year to keep it small enough to harvest the leaves for tea, which is rich in caffeine. Even so, it can still become a very substantial-sized plant with thick roots. You don't say where you're going to grow it... It will need a frost-free location though it can stand temps down to zero if kept very dry. Another feature is that being a native of dense forests the young plants do not like long periods of strong sunlight. Good luck!