Apparently, poplars don't just grow to 40 feet, and then stop. Most varieties carry on to reach greater heights, but, at some point, they all grow to 40 feet, and then some!
Cereus (ˈsɪərɪəs)
n
1. (Plants) any tropical American cactus of the genus Cereus, esp C. jamacaru of N Brazil, which grows to a height of 13 metres (40 feet)