Family: Asteraceae

An herbaceous perennial that spreads from initial plantings. Mexican sunflower is native to Mexico and Central America. It was introduced around the world as an ornamental, for a green manure source, and as erosion control. Today, it is considered invasive in Asia, Africa, and other Pacific Islands.

Mexican sunflower is very difficult to maintain in a garden setting. New plants will sprout from any tiny piece of root or vegetation. It forms dense thickets and is allelopathic; other species cannot grow where Mexican sunflower has taken hold. It can invade gardens, orchards, fields, along with disturbed areas.

*This plant is common at low elevations in Hawaii. Some have confused Mexican sunflower (Tithonia diversifolia) for Jerusalem artichoke (Helianthus tuberosus). One big difference is the petal tips, T. diversifolia has three teeth at the tip while H. tuberosus has a pointed end.

Description and Dispersal:

• Herbaceous perennial growing up to 15 feet
  
• Hollow stems are slightly ridged and are covered in fine hair
  
• Leaves are alternately arranged, 3 to 5 lobed, and have toothed or scalloped margins
  
• Grey-green hair covers the leaves
  
• Sunflower-like heads are born in small groups at the ends of branches
  
• Yellow petals, 7 to 15 in number, have three small teeth an the ends
  
• Seeds can spread unintentionally as a contaminant
  
• Seeds can be spread by means of external attachment on animals
  
• Seeds are wind, water, and human dispersed

High Risk Traits:

• Elevation range exceeds 1000 m, demonstrating environmental versatility
  
• Thrives in tropical climates
  
• Naturalized on Kauai, Oahu, Maui and Hawaii (Hawaiian Islands) and widely naturalize elsewhere
  
• Disturbance and crop weed; potential environmental weed
  
• Other Tithonia species are invasive
  
• Allelopathic
  
• Tolerates many soil types
  
• Forms dense stands
  
• Reproduces by seeds and vegetatively by suckers, fragments and coppices
  
• Able to reach maturity in <1 year in certain environments
  
• Seeds and fragments dispersed by wind, water, animals, people and as a contaminant
  
• Prolific seed production
  
• Able to coppice and resprout after cutting

Low Risk Traits:

• Unarmed (no spines, thorns, or burrs)
  
• Provides fodder for livestock (palatable despite reports of toxicity)
  
• Ornamental
  
• Thrives in full sun (may limit spread into shaded habitats)
  
• Herbicides may provide effective control