 Two species, "T. diversifolia" and "T. rotundifolia", are widely cultivated and have escaped to become weeds in tropical and subtropical areas around the world.The distinguishing feature of the genus is the peduncle, which is fistulose (meaning hollow and flaring toward the apex).The plants are coarse annual or perennial herbs or shrubs, and one species, "T. koelzii", is a small tree.