Family: Lamiaceae

Origin, Description & Uses:
Vitex trifolia, commonly known as simpleleaf chastetree or Arabian lilac, is native to tropical and subtropical regions of Asia, Australia, and the western Pacific. This fast-growing shrub or small tree typically reaches 6–20 feet (2–6 m) tall and features aromatic, gray-green leaves with three leaflets, spikes of blue to violet flowers, and small dark purple to black fruits. It is widely cultivated as an ornamental for its attractive flowers, fragrant foliage, and tolerance of heat, drought, wind, and coastal conditions. In some regions, it has also been used in traditional medicine and for erosion control.

Risks & Threats:
Vitex trifolia is naturalized in Hawaiʻi and possesses traits that are cause for concern. It produces abundant bird-dispersed seeds, grows rapidly, and can establish in coastal vegetation, disturbed sites, dry forests, and other natural habitats. These characteristics allow it to spread beyond cultivation, where it may form dense stands that compete with native plants and alter tropical island ecosystems. Because this species is already naturalized on Oʻahu and Molokaʻi and is potentially naturalizing on Kauaʻi, Maui, and Hawaiʻi Island, planting it may contribute to its continued spread. Whenever possible, choose a low-risk or native alternative for landscaping. In areas where Vitex trifolia is already widespread, avoid planting it near natural areas and manage existing populations to help prevent further spread into sensitive ecosystems.

High Risk Traits:

• Broad climate suitability (Zones 9–11; wide elevational range)
  
• Native and naturalized across multiple tropical/subtropical regions
  
• Repeatedly introduced outside native range as ornamental/medicinal plant
  
• Naturalized in Florida, Hawaii, and elsewhere
  
• Hawaiian Islands status: Naturalized on O'ahu and Moloka'i; potentially naturalizing on Kaua'i, Maui, and Hawai'i
  
• Listed as FLEPPC Category II invasive weed
  
• Aggressive pasture weed in New Caledonia and Fiji
  
• Congeneric is highly invasive
  
• Produces viable seed
  
• Self-compatible
  
• Reproduces vegetatively (fragmentation)
  
• Actively dispersed by people (ornamental/medicinal use)
  
• Bird-dispersed (fleshy drupes survive gut passage)
  
• Tolerates a wide range of soil types
  
• Forms dense thickets

Low Risk Traits:

• Lacks spines, thorns, or burrs
  
• Palatable to grazing animals
  
• Non-toxic to vertebrates
  
• Not shade tolerant
  
• No external attachment for dispersal
  
• Not wind-dispersed
  
• Low seed density (large fruits)
  
• Controllable with herbicides (glyphosate/imazapyr)