Gomphocarpus species (Swan plant)Gomphocarpus fruticosus, Gomphocarpus physocarpus

Kingdom: Plantae
(Unranked): Angiosperms
(Unranked): Eudicots
(Unranked): Asterids
Order: Gentianales
Family: Apocynaceae
Subfamily: Asclepiadoideae
Genus: Gomphocarpus
Species: G. physocarpus
Binomial name: Gomphocarpus physocarpus and Gomphocarpus fruticosus
Synonyms: Asclepias physocarpa, Asclepias brasiliensis, Gomphocarpus brasiliensis
Common names: Swan plant, Swanplant, Balloon plant, Balloon cotton-bush, Balloonplant, Family Jewels, Monkeyballs, Oscar, Hairy Balls, Giant Swan Milkweed.

Gomphocarpusis is a species of milkweed. The plants are native to southeast Africa, but they have been widely naturalised. They are often used as an ornamental plant. The name "balloon plant" is an allusion to the swelling bladder-like pods which are full of seeds.
These undershrub perennial herbs can grow to over 2 m in height. The plants bloom in warmer months. They prefer moderate moisture, as well as sandy and well-drained soil and full sun.
The flowers are small, with white hoods and about 1 cm across. The capsule is a pale green and the shape of an inflated sphere. It is covered with rough hairs. It reaches 8 cm in diameter. The leaves are light green, linear to lanceolate and up to 10 cm long, 1.2 cm broad. The seeds have silky tufts (pappus).

The plants are a food source for the caterpillars of Danaus butterflies, and is a specific Monarch butterfly food and habitat plant. It is also popular in traditional medicine to cure various ailments. All of the milkweeds are named for a milky sap in the plant's stem and leaves. After the Monarch caterpillar has metamorphosed into a butterfly, the alkaloids from the sap they ingested from the plant are retained in the butterfly, making it unpalatable to predators.

Late July.