Family: Euphorbiaceae

Origin, Description & Uses:
Euphorbia stenoclada, commonly known as silver thicket, is a spiny, succulent shrub native to the dry forests and thorn scrub regions of southwestern Madagascar. It typically forms dense, tangled thickets of upright, silvery-gray branches armed with sharp spines, an adaptation that helps it conserve water and deter herbivores in arid environments. Like other members of the Euphorbia family, it produces a milky latex sap and has small, specialized flowers. This species is sometimes cultivated as an ornamental for xeriscaping, collectors’ gardens, or as a natural barrier hedge due to its striking appearance and impenetrable growth form. Its drought tolerance and architectural shape make it appealing for low-water landscapes.

Risks & Threats:
Although Euphorbia stenoclada is not currently known to be naturalized in Hawaii, it possesses several traits that are cause for concern and warrant further evaluation. Many Euphorbia species have a history of becoming invasive in warm climates, and this species’ ability to thrive in dry tropical conditions suggests it could establish in similar environments. Its dense, spiny growth can form difficult-to-remove thickets, while its toxic, caustic latex may pose risks to people, pets, and livestock and deter grazing, allowing populations to persist unchecked. Reproduction by seed and potential spread through cultivation further increase its risk profile. Because of these characteristics, additional assessment is needed to determine whether silver thicket could negatively impact Hawaii’s ecosystems if it were to escape cultivation.

High Risk Traits:

• Congeneric weed (other Euphorbia species are invasive)
  
• Produces spines
  
• Toxic to humans (sap causes skin and eye irritation)
  
• Tolerates wide range of soil conditions
  
• Naturalized outside native range (East Africa, Hawaii, US mainland)
  
• Intentionally dispersed by people (ornamental trade)
  
• Forms dense thickets
  
• Produces viable seed

Low Risk Traits:

• Not documented as a weed elsewhere
  
• Limited climate suitability (frost-sensitive; USDA zones 10–11)
  
• Not parasitic, shade-tolerant, or climbing
  
• Not dispersed by birds or water
  
• Unlikely to be a produce contaminant