Family: Acanthaceae

Origin, Description & Uses
Thunbergia laurifolia (purple allamanda, laurel-leaved thunbergia) is a vigorous, twining perennial vine native to tropical Asia, ranging from Arunachal Pradesh through Peninsula Malaysia. It is prized as an ornamental for its lush foliage and abundant clusters of large, lavender to violet trumpet-shaped flowers that bloom over an extended season. Its rapid growth allows it to quickly cover fences, arbors, trellises, and other structures, making it a popular choice for screening and tropical landscapes. It has also been cultivated in some regions for traditional medicinal uses.

Risks & Threats
Purple allamanda is naturalized in Hawaiʻi on Kauaʻi, Oʻahu, Lānaʻi, Maui, and Hawaiʻi Island. This species possesses traits that are cause for concern, including rapid growth, prolific seed production, and the ability to spread vegetatively, allowing it to escape cultivation and invade forests, stream corridors, roadsides, and other disturbed habitats. Dense growth can smother native vegetation, blanket shrubs and trees, and reduce biodiversity, making it a threat to tropical island ecosystems. Because this species is already widely established in Hawaiʻi, further planting should be avoided, and existing plants should be carefully managed to prevent their spread into natural areas or regions where they are not yet common. Whenever possible, choose a low-risk or native alternative for landscaping to help protect Hawaiʻi’s unique ecosystems.

High Risk Traits:

• Broad climate tolerance (USDA zones 10a–11; naturalized at 0–850 m)
  
• Already naturalized in Hawaii, Fiji, French Polynesia
  
• Naturalized on multiple Hawaiian Islands: Kauaʻi, Oʻahu, Lānaʻi, Maui, and Hawaiʻi
  
• Environmental weed in Australia (alert list)
  
• Congeneric (T. grandiflora) is a serious weed
  
• Vigorous vine that smothers and kills trees
  
• Spreads vegetatively via cuttings and flood-dispersed fragments
  
• Extensive tubers enable resprouting after damage
  
• Intentionally spread as ornamental; also spread via garden waste
  
• Herbicide control is difficult (rarely 100% effective)

Low Risk Traits:

• No spines, thorns, or burrs
  
• Non-toxic to humans and animals
  
• Requires full sun (not shade-tolerant)
  
• Narrow soil pH tolerance (6.1–7.8)
  
• Poor seed dispersal (no wind, bird, or external animal dispersal)
  
• Low seed production (2–4 seeds per capsule)