Bishop’s Balls, Swan Plant, Cotton-bush, Nailhead, Balloon Plant
Balloon milkweed (Asclepias physocarpa), a member of the Apocynaceae (Dogbane Family), is a herbaceous to subshrub perennial (zones 8-10) and annual elsewhere that grows to 6 feet and has pink and white flowers that bloom in the summer.
More information about Balloon Milkweed can be found on this blog post.
Monarch Butterfly (Danaus plexippus)
Many other butterflies use this plant as a nectar source.
Balloon milkweed is found in sandy tropical habitats. It has been planted in South Carolina and California and can be invasive in tropical regions.
The species is the Latin name for bladders (Missouri Botanical Garden), referring to the fruits of the plant.