Family: Asteraceae

Cosmos bipinnatus (garden cosmos, Mexican aster) is an annual flowering plant native to Mexico and Central America. It is widely grown around the world for its airy, fern-like foliage and showy daisy-like flowers, which range in color from white and pink to deep magenta. Garden cosmos is popular in home gardens, parks, and roadside plantings because it grows quickly, thrives in full sun, and blooms over a long season with minimal care. It is often used in wildflower mixes, pollinator gardens, and as a cut flower due to its tall, graceful stems and abundant blossoms that attract bees and butterflies.

Although Cosmos bipinnatus is not currently known to be naturalized in Hawaiʻi, it possesses several traits that are cause for concern in tropical island ecosystems. The plant produces large quantities of easily dispersed seeds, grows rapidly, and tolerates a wide range of soil and moisture conditions—characteristics commonly associated with species that escape cultivation. If introduced repeatedly or allowed to spread unmanaged, it could establish self-sustaining populations and compete with native plants in disturbed areas. To help protect Hawaiʻi’s unique ecosystems, it is recommended that gardeners choose low-risk, non-invasive plants or native alternatives that provide similar ornamental and pollinator-friendly benefits without the potential ecological risks.

High Risk Traits:

• Thrives in tropical climates
  
• Elevation range exceeds 1000 m
  
• Widely naturalized
  
• A garden and disturbance weed
  
• Other Cosmos species have become invasive
  
• Conflicting reports on possible toxicity
  
• A mild allergen
  
• Tolerates many soil types
  
• Can from dense stands that may potentially exclude other vegetation
  
• Seeds freely
  
• The plant can regenerate from a small piece of stem
  
• Annual – able to reach maturity in one growing season
  
• Seeds dispersed intentionally by people and externally on animals and possibly machinery or clothing

Low Risk Traits:

• Unarmed (no spines, thorns or burrs)
  
• Requires full sun
  
• Self-incompatible
  
• Used as an ornamental and to attract and benefit pollinators