Family: Asteraceae

Origin, Description & Uses:
Tithonia rotundifolia, commonly known as Mexican sunflower, is native to Mexico and Central America. This fast-growing annual produces tall, branching stems and large, bright orange to reddish-orange daisy-like flowers that bloom over a long season. Its showy flowers attract butterflies, bees, and other pollinators, making it a popular ornamental in gardens. It is also sometimes planted as a seasonal screen, used in cut flower arrangements, or grown as a cover crop or green manure because it produces abundant leafy biomass.

Risks & Threats:
Mexican sunflower is naturalized in Hawaiʻi and possesses traits that are cause for concern. It grows rapidly, produces large numbers of wind- and water-dispersed seeds, and readily colonizes roadsides, disturbed areas, pastures, and open natural habitats. Dense stands can outcompete native vegetation and other desirable plants, increasing the risk of further spread into tropical island ecosystems. Because this species is already widespread in parts of Hawaiʻi, planting it in new areas may contribute to its continued expansion. To help protect Hawaiʻi’s unique ecosystems, avoid planting Mexican sunflower in areas where it is not yet widely established, manage existing populations to prevent seed production and spread, and choose a low-risk or native alternative when suitable options are available.

High Risk Traits:

• Elevation range exceeds 1000 m, demonstrating environmental versatility
  
• Thrives in tropical climates
  
• Naturalized on Hawaii Island and widely naturalized elsewhere
  
• A disturbance and crop weed (but no documented impacts in Hawaiian Islands to date)
  
• Other Tithonia species are invasive weeds
  
• May be allelopathic
  
• Possibly unpalatable to deer
  
• Tolerates half-shade
  
• Tolerates many soil types
  
• Forms dense stands in Africa
  
• Reproduces by seeds
  
• Hybridizes with other Tithonia species
  
• Reaches reproductive maturity rapidly (2+ months from seed)
  
• Seeds dispersed by animals, water and on clothing, Also spread in dumped garden waste and contaminated agricultural produce
  
• Prolific seed production

Low Risk Traits:

• Unarmed (no spines, thorns, or burrs)
  
• Provides fodder for cattle
  
• Non-toxic
  
• Ornamental
  
• Self-incompatible
  
• Not reported to spread vegetatively
  
• Herbicides may provide effective control
  
• Does not tolerate cutting or slashing