Family: Asteraceae

Origin, Description & Uses:
Senecio sylvaticus (heath groundsel, wood groundsel) is an annual herb native to Macaronesia and much of Europe extending to the Caucasus region. It typically grows in disturbed sites such as roadsides, pastures, forest edges, and open grasslands. The plant produces upright, branching stems with lobed, softly hairy leaves and small yellow, daisy-like flower heads. Like many members of the daisy family, it produces abundant wind-dispersed seeds that support rapid spread in suitable habitats. It has no known significant ornamental or economic uses and is generally considered a common weed in many regions where it has been introduced.

Risks & Threats:
This species is naturalized on Oʻahu, Molokaʻi, Maui, and Hawaiʻi Island, where it is usually found in open, relatively dry sites but can also occur in wetter habitats, typically at elevations from about 1,500 to 3,200 m. Senecio sylvaticus possesses traits that are cause for concern, including fast growth, prolific seed production, and an ability to establish in disturbed environments, allowing it to compete with and displace native and low-stature vegetation. Its presence across multiple islands and wide habitat tolerance increases the likelihood of further spread into sensitive upland and native ecosystems. Because it is naturalized and capable of expanding, it could detrimentally impact tropical island ecosystems. In areas where it is not yet widespread, preventing further introduction can help reduce additional impacts.

High Risk Traits:

• Elevation range exceeds 1000 m, demonstrating environmental versatility
  
• Able to grow in tropical climates
  
• Widely naturalized, including on Oahu, Molokai, Maui, and Hawaii
  
• A disturbance-adapted weed
  
• Other Senecio species are invasive
  
• Can be toxic to animals if consumed in large quantities
  
• Alternate host of Plum pox virus (PPV)
  
• Can form dense cover as an early successional plant
  
• Reproduces by seeds
  
• Hybridizes with Senecio viscosus
  
• Self-fertile
  
• Annual growth habit
  
• Seeds dispersed by wind, and accidentally due to human activities
  
• Pappus can stick to people, shoes, clothing, vehicles, or machinery, especially when wet
  
• Prolific seed production
  
• Seeds may persist in the soil

Low Risk Traits:

• Unarmed (no spines, thorns or burrs)
  
• Palatable to sheep and goats, but toxic to others
  
• Shade-intolerant
  
• Not reported to spread vegetatively
  
• Herbicides may provide effective control