The botanical name for this plant is Gomophocarpus physocarpus but it has many easier to pronounce common names including balloon plant, balloon cotton bush, bishop's balls, and swan plant. It is a species of milkweed and was previously called Asclepias physocarpa.
The balloon plant is a perennial shrub native to south east Africa but has been introduced to many countries around the world, becoming naturalised in most of them including the Mediterranean.
When the balloon plant is fully grown it can reach two metres high. It has long narrow leaves and small white flowers with purple accents which appear all year round in moderate climates. The large, balloon-like seed pods form after the flowers have been pollinated by wasps, usually the harmless mud dauber wasps but other species have also been known to visit the flowers. The seed pods turn a tan colour before splitting open releasing the small brown seeds which have silken hairs to aid wind dispersal.
The balloon plant grows quite tall and lanky and may need staking or it can be cut back in spring to promote bushier growth. It is not frost hardy and will need protection in the winter in colder inland areas. It can however, withstand some drought. It will flower best in full sun but can be grown in partial shade.
Propagation is by seed or by stem cuttings but as all parts of this plant are poisonous gloves should be worn when handling it. Although the balloon plant is toxic to humans and animals, the Monarch butterfly larva is not affected and stores the poisonous alkaloids in their bodies, which passes from pupa through to adult stage, and makes them taste foul to predators.
In traditional medicine, the dried leaves are ground into a powder and taken like snuff to treat headaches and the milky latex is said to make warts disappear. The seeds, when blown out of the pods are said to act as a charm to placate ancestors and the fresh stems plunged into mole holes are said to deter moles.