Family: Cyatheaceae

Origin, Description & Uses
Sphaeropteris medullaris (black tree fern) is a striking tree fern native to New Zealand. It is known for its tall, erect trunk, which can reach up to 20 meters in height, topped with a crown of large, feathery fronds that can span several meters across. The trunk is dark and fibrous, giving the species its common name. Black tree ferns are often grown as ornamental plants in tropical and subtropical gardens because of their dramatic, prehistoric appearance. They thrive in moist, shaded environments and can be used to add texture and vertical interest to landscapes, as well as for educational or conservation-focused plantings.

Risks & Threats
Although Sphaeropteris medullaris is not currently known to be naturalized in the Hawaiian Islands, it possesses traits that could pose ecological risks. Its large size, prolific spore production, and ability to grow in diverse shaded habitats could allow it to spread rapidly if introduced, potentially outcompeting native understory species. For tropical island ecosystems that are highly sensitive to invasive plants, this species could alter habitat structure and biodiversity. For these reasons, it is recommended to choose a low-risk or native alternative when possible, particularly in natural or semi-natural areas.

High Risk Traits:

• Native to tropical/subtropical climates (Fiji, NZ)
  
• Congeneric is invasive in Hawaii
  
• Tolerates wide range of soil conditions
  
• Shade tolerant
  
• Forms dense monospecific stands
  
• Produces viable spores (seed equivalent)
  
• Spores wind-dispersed
  
• Spores water-dispersed
  
• Prolific spore production (>1000/m²)
  
• Frond scales reported as skin irritant

Low Risk Traits:

• No evidence of naturalization beyond native range
  
• Not listed as a weed (garden, agricultural, or environmental)
  
• No spines, thorns, or burrs
  
• Not toxic to animals or humans
  
• Does not reproduce vegetatively
  
• Frost-sensitive (limited to USDA zones 9-11)