It has a plethora of common names including balloon plant, balloon cotton-bush, balloon milkweed, bishop's balls, elephant balls, hairy balls.
Gomphocarpus physocarpus, commonly known as hairy balls, balloonplant, balloon cotton-bush, bishop's balls, nailhead, or swan plant, is a species of milkweed. The plant is native to southeast Africa, but it has been widely naturalized. Tropical Flowering Plants: A Guide to Identification and Cultivation. Timber Press. p.
Gomphocarpus physocarpus: Asclepias physocarpa is the former botanical name , Goose plant, Giant swan plant, Hairy balls, Family jewels, Oscar, Cotton-bush.