Family: Lamiaceae

Origin, Description & Uses:
Chaste tree (Vitex agnus-castus) is a small deciduous tree or large shrub native to southern Europe that has been widely cultivated in warm temperate and subtropical regions around the world. Growing up to about 15 feet (4.5 m) tall, it features attractive palmately compound leaves with five to nine narrow leaflets, long spikes of fragrant pale lilac-blue flowers, and small brown fruits that persist after flowering. Its ornamental flowers attract bees and other pollinators, making it a popular choice for gardens and landscapes. The fruits and leaves have also been used for centuries in traditional herbal medicine.

Risks & Threats:
Although Vitex agnus-castus is currently not known to be naturalized in the Hawaiian Islands, it possesses biological traits that are cause for concern. It produces abundant seeds, is capable of establishing in a variety of habitats, and has become naturalized or invasive in several regions outside its native range. These characteristics suggest it has the potential to spread beyond cultivation and negatively impact tropical island ecosystems by establishing in disturbed areas and competing with native vegetation. To help protect Hawaiʻi’s unique natural environments, Plant Pono recommends choosing a low-risk or native alternative whenever suitable alternatives are available.

High Risk Traits:

• Broad climate tolerance (USDA zones 5–11)
  
• Widely introduced via cultivation
  
• Naturalized in the southeastern U.S. and elsewhere
  
• Self-seeds and becomes weedy in gardens
  
• Forms dense thickets
  
• Unpalatable to deer and rabbits
  
• Tolerates a wide range of soils and drought
  
• Produces abundant viable seed annually
  
• Dispersed intentionally by people
  
• Water-dispersed (riparian habitats)
  
• Bird-dispersed (seeds survive gut passage)
  
• Resprouts after cutting or pruning

Low Risk Traits:

• No spines, thorns, or burrs
  
• Not toxic to animals
  
• No evidence of vegetative spread in the wild