Good Answer

In fact, the winner is a Montezuma bald cypress. El Arbol de Tule, in Mexico, has a trunk 11.5 m in diameter and 36 m in circumference (measured in 1998). The most imposing specimen at the Montréal Botanical Garden, a cottonwood, "only" has a diameter of 1.54 m and a circumference of 4.8 m.