Family: Asteraceae

Ambrosia artemisiifolia (common ragweed, annual ragweed) is an annual plant native to North America. Traditionally, it has been used as a medicinal plant by the Cherokee, Lakota, Iroquois, Dakota, and Delaware tribes. In addition, it has played a role in some remediation projects, particularly in removing lead from contaminated soil.

However, despite these beneficial uses, the plant is primarily known for its ability to cause severe allergic reactions and hay fever. It is also a widely naturalized invasive species, found on Oʻahu, Maui, Molokai, and Hawaiʻi Island. Beyond its allergenic effects, common ragweed poses additional hazards: it has small sharp spines, is potentially toxic to browsing animals, and may cause dermatitis upon contact. This persistent weed can survive in a seed bank for up to 40 years, forms dense stands, and is capable of withstanding mowing, grazing, and trampling.

High Risk Traits:

• Broad climate suitability
  
• Naturalized on Kauai, Oahu, Molokai, Maui and Hawaii (Hawaiian Islands), and widely naturalized elsewhere
  
• A disturbance-adapted weed that can impact agriculture and the natural environment
  
• Other Ambrosia species are invasive
  
• Achenes with small, sharp spines
  
• Allelopathic
  
• Potentially toxic to browsing and grazing animals
  
• Highly allergenic pollen, and may cause contact dermatitis
  
• Tolerates shade (but thrives in full sun)
  
• Tolerates many soil types
  
• Able to form dense stands that may exclude other vegetation and reduce species richness
  
• Reproduces through prolific seed production
  
• Hybridizes with other Ambrosia species
  
• Autogamous
  
• Reaches maturity in <1 year
  
• Seeds dispersed as a contaminant of crops and bird seed, via agricultural machines, vehicles and soil movement, by water, and internally and externally by birds and other animals
  
• Capable of forming a persistent seed bank (up to 40 years)
  
• Tolerates mowing, trampling and grazing

Low Risk Traits:

• Primarily a weed of disturbance and roadsides in the Hawaiian Islands
  
• Palatable to goats and cattle, despite potential toxicity
  
• Not reported to spread vegetatively
  
• Herbicides can provide effective control