I still stand in awe each time I see the cannon ball tree (Couroupita guianensis), a member of the Brazil nut family. In fact, it is such an astonishing plant that I am nominating it as the most interesting tree on Earth (disclaimer: I am a specialist in the Brazil nut family and my nomination may be biased). After you read this essay, I would like to know if you agree with me—if not, I challenge you to nominate a tree, tropical or temperate and from any part of the world, that you feel is more interesting than this marvel of nature.