|Photo of balloonplant with capsules|
|Detail photo of balloonplant capsules|
Gomphocarpus physocarpus E.Mey.
Asclepias physocarpa (also known as Gomphocarpus physocarpus, commonly balloonplant, balloon cotton-bush or swan plant) is a species of milkweed. The plant is native to southeast Africa, but it has been widely naturalized. It is often used as an ornamental plant. The name "balloonplant" is an allusion to the swelling bladder-like pods which are full of seeds.
Asclepias physocarpa is an undershrub perennial herb, that can grow to over six feet. The plant blooms in warm months. It grows on roadside banks, at elevations of 2800 to 5000 feet above sea level. The plant prefers 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 in shape an inflated sphere. It is covered with rough hairs. It reaches three inches in diameter. The leaves are light green, linear to lanceolate and 3 to 4 inches long, 1.2 cm broad. The seeds have silky tufts.
The plant is 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.
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