Family: Apiaceae

Origin, Description & Uses:
Torilis arvensis (spreading hedge parsley) is native to a broad region spanning Europe to Central Asia and Pakistan, as well as Macaronesia, North Africa, and the Arabian Peninsula. It is an annual to biennial herb in the carrot family (Apiaceae) that typically grows in open, disturbed sites. The plant produces finely divided, fern-like leaves and small clusters of white flowers arranged in umbrella-shaped inflorescences. Its fruits are covered in tiny hooked bristles that readily cling to clothing, fur, and feathers, aiding in dispersal. While it has had limited traditional medicinal use in parts of its native range, it is more commonly regarded as a minor agricultural weed rather than a cultivated or ornamental species.

Risks & Threats:
In Hawaiʻi, Torilis arvensis is naturalized on Kauaʻi and Maui and exhibits traits that are cause for concern, including prolific seed production and highly effective hitchhiking burrs that spread easily through human activity and animals. It can establish in disturbed habitats such as roadsides, pastures, and dry grasslands, where it may compete with desirable vegetation and contribute to declines in local biodiversity. Once established, it can be difficult to control due to its persistent seed bank and efficient dispersal strategy. Although not yet widespread across the islands, it has the potential to expand and negatively impact tropical island ecosystems if left unmanaged. This species is naturalized, possesses traits that are cause for concern, and could detrimentally impact Hawaiʻi’s ecosystems; where possible, low-risk or native plant alternatives should be chosen. In areas where it is not yet widely established, preventing further spread and removing new infestations is strongly recommended to minimize future impacts.

High Risk Traits:

• Broad climate and soil tolerance (temperate, Mediterranean, calcareous/gravelly/clay soils)
  
• Naturalized widely in North America and introduced to Hawaii
  
• Kaua'i and Maui Naturalized (established on both islands)
  
• History of repeated introductions outside native range
  
• Weeds of disturbed sites (roadsides, fields, orchards, woodlands)
  
• Listed as environmental weed (Cal-IPC "Moderate") and Class B noxious weed (WA)
  
• Congeneric species (T. japonica) also invasive
  
• Host for tarnished plant bug (agricultural pest)
  
• Produces viable seed; seed banks may exceed 1,000 seeds/m²
  
• Self-compatible (can self-pollinate)
  
• Annual; matures within one year
  
• Dispersed externally by animals (fur/feathers), water, and humans (clothing, tires, mud)
  
• Persistent seed bank (>1 year dormancy)

Low Risk Traits:

• Not suited to lowland tropical climates (limited to high elevations in Hawaii)
  
• Not toxic to humans or animals
  
• No spines, thorns, or allelopathic properties
  
• Not shade-tolerant (prefers full sun)
  
• No vegetative reproduction (seed only)
  
• Easily controlled with common herbicides (glyphosate, triclopyr, etc.)