Family: Apocynaceae

Origin, Description & Uses
Gomphocarpus physocarpus, commonly known as balloon plant, balloon cottonbush, or swanplant, is native to southeastern Africa. It is a fast-growing, perennial shrub that can reach up to 2–3 meters in height, featuring narrow, lance-shaped leaves and clusters of small, fragrant white flowers. The plant is especially recognized for its distinctive balloon-like seed pods, which turn brown as they mature and release fluffy seeds. While it has been cultivated as an ornamental garden plant and as a host for monarch butterflies, its striking appearance and unique seed pods make it popular in horticulture.

Risks & Threats
This species is naturalized in Hawaii and possesses traits that are cause for concern. Gomphocarpus physocarpus produces large numbers of seeds that are easily dispersed by wind, allowing it to spread rapidly into natural areas. It can form dense stands that outcompete native vegetation, reduce biodiversity, and alter habitat structure in tropical island ecosystems. Gardeners and landscapers are encouraged to carefully manage this species or consider native or low-risk alternatives to help protect Hawaii’s delicate natural environments.

High Risk Traits:

• Elevation range exceeds 1000 m, demonstrating environmental versatility
  
• Thrives in tropical climates
  
• Naturalized on all the Hawaiian Islands (except Niihau and Kahoolawe), and widely naturalized elsewhere
  
• A weed of pastures, reducing forage due to toxicity
  
• Environmental weed, competing with native plants
  
• Other Gomphocarpus species have become invasive
  
• Toxic to browsing animals if eaten accidentally (but unpalatable)
  
• Sap toxic and allergenic to people
  
• Forms dense thickets
  
• Produces viable seed
  
• Hybridizes with other Gomphocarpus species
  
• Reaches maturity in <1-2 years
  
• Seeds, in mud, adhere to animal pelts, machinery and other vehicles
  
• Seeds spread as a contaminant of hay and chaff
  
• Seeds wind-dispersed
  
• Seeds and fruit are buoyant and able to be spread by water

Low Risk Traits:

• Unarmed (no spines, thorns or burrs)
  
• Ornamental and medicinal uses
  
• Self-incompatible
  
• Not reported to spread vegetatively
  
• Herbicides provide effective control
  
• A host plant of Monarch butterflies (Danaus plexippus)