Family: Euphorbiaceae

Euphorbia tirucalli (Indian tree-spurge, pencil cactus) is a hardy and drought-tolerant succulent that is often grown as an ornamental in gardens and as a potted plant. It is native to Africa and likes semi-arid climates. It is commonly cultivated as an ornamental because of its numerous slender, cylindrical colorful branches that resemble pencils or sticks. These branches are green, but they can turn bright red or orange when exposed to direct sunlight, especially during stress or drought conditions. It is widely naturalized throughout the tropic and subtropic regions of the world, including Kauaʻi, Hawaiʻi Island and Oʻahu. This plant is known for its toxic milky latex sap which can cause severe skin irritation, burning to the lips and mouth if ingested, and temporary blindness. It is advised to use gloves and eye protection during handling for one’s safety.

High Risk Traits:

• Broad climate suitability and elevation range
  
• Naturalized on Kauai, Hawaii, and Oahu (Hawaiian Islands) and widely naturalized elsewhere
  
• A potential landscaping or environmental weed due to toxic sap and ability to form dense thickets
  
• Other Euphorbia species are invasive weeds
  
• Sap poisonous to animals and people
  
• Tolerates many soil types
  
• Forms dense thickets that may impede movement or exclude other vegetation
  
• Reproduces by seeds (at least within native range) and vegetatively by rooting stems and fragments
  
• Seeds, if produced, reportedly spread by birds, water and intentional cultivation
  
• Coppices and resprouts after cutting or physical damage

Low Risk Traits:

• Unarmed (no spines, thorns, or burrs)
  
• Palatable to goats and sheep at younger stages of growth (despite toxic sap)
  
• Grows best in high light environments (dense shade may inhibit spread)
  
• Dioecious (although some plants may be monoecious)
  
• Limited fruit and seed production in cultivation limits risk of long distance or accidental dispersal
  
• Herbicides may provide effective control