Family: Pteridaceae

Adiantum raddianum, commonly known as the delta maidenhair fern, is a delicate and graceful fern valued worldwide as a houseplant and ornamental species. It is easily recognized by its fine, wiry black stems and small, fan-shaped fronds that create a soft, lacy texture. Native to tropical regions of South America, this fern thrives in shaded, moist environments such as forest understories, rocky crevices, and along streambanks. Its ability to spread by spores, along with its popularity in cultivation, has allowed it to establish populations outside of its native range.

In Hawaiʻi, Adiantum raddianum has become naturalized on Kauaʻi, Oʻahu, Molokaʻi, Lānaʻi, Maui, and Hawaiʻi Island. It is often found growing in moist, shaded habitats similar to those it occupies in its native range, where it can displace native plants by forming dense colonies. While it is still commonly sold as an ornamental plant, its naturalization across multiple islands highlights the need for awareness of its invasive potential. Planting alternatives that are non-invasive can help prevent further spread into native ecosystems.

High Risk Traits:

• Adapted to tropical/subtropical climates
  
• Broad environmental versatility
  
• Repeatedly introduced worldwide as an ornamental
  
• Naturalized outside its native range (e.g., Hawaii, New Zealand)
  
• Environmental weed that displaces native species
  
• Tolerant of shade
  
• High spore production
  
• Reproduces by vegetative fragmentation (rhizomes)
  
• Dispersed by wind, water, and unintentionally by humans (clothing, shoes)
  
• Intentionally dispersed by people (horticulture trade)

Low Risk Traits:

• Non-toxic to humans and animals
  
• Not parasitic or allelopathic
  
• Lacks spines, thorns, or burrs
  
• Does not create a fire hazard
  
• Sensitive to mutilation and disturbance