Family: Asteraceae

Origin, Description & Uses
Erigeron karvinskianus, commonly known as Mexican daisy or Santa Barbara daisy, is a low-growing, spreading perennial native to Mexico and parts of Central America. It is widely cultivated as an ornamental groundcover due to its delicate, daisy-like flowers that shift from white to pink as they age, creating a soft, multicolored effect. This species thrives in a variety of conditions, including poor soils, rocky slopes, and garden edges, and is often used in landscaping for borders, hanging baskets, and erosion control because of its ability to quickly form dense mats.

Risks & Threats
Mexican daisy is naturalized in Hawaii and poses a high risk due to its aggressive spreading habit and ability to thrive in a wide range of environments. It readily escapes cultivation, establishing in natural areas such as cliffs, roadsides, and coastal habitats, where it can outcompete native vegetation. Its prolific seed production and tolerance of drought and disturbance make it difficult to control once established. Because it possesses traits that are cause for concern and could detrimentally impact tropical island ecosystems, planting this species is discouraged. Gardeners and landscapers are encouraged to choose low-risk or native alternatives that support Hawaii’s unique ecosystems without contributing to invasive spread.

High Risk Traits:

• Naturalized in California, New Zealand, and Hawaii
  
• Major environmental weed in Hawaii and La Réunion
  
• Forms dense stands; illegal to sell in New Zealand
  
• Competes with and threatens endangered native plants
  
• Congeneric weeds exist (e.g., E. canadensis)
  
• Forms dense mats that smother other vegetation
  
• Prolific seed producer (100+ flower heads/m²)
  
• Wind-dispersed seeds
  
• Commonly planted as an ornamental
  
• Can spread via contaminated soil and potting mix
  
• Tolerates a wide range of soil types
  
• Suited to tropical and subtropical climates

Low Risk Traits:

• Not a weed in gardens, agriculture, or forestry
  
• Lacks spines, thorns, or burrs
  
• No evidence of toxicity to animals or humans
  
• Not allelopathic or parasitic
  
• Requires full sun; not shade tolerant
  
• Vegetative spread is rare
  
• No specialist pollinators required
  
• Seeds lack attachment structures
  
• Not dispersed by water or birds
  
• Well controlled by herbicides