Family: Equisetaceae

Origin, Description & Uses
Equisetum variegatum, commonly known as variegated horsetail, is a perennial, grass-like plant native to much of the Northern Hemisphere, including parts of North America, Europe, and Asia. This ancient plant belongs to the horsetail family, a lineage that dates back hundreds of millions of years. It grows as stiff, hollow, segmented stems that are typically green with dark bands at the joints, giving the plant a distinctive striped or “variegated” appearance. Variegated horsetail spreads through underground rhizomes and often forms dense patches in wet or sandy habitats such as riverbanks, wetlands, and disturbed areas. Because of its unusual structure and ability to thrive in moist soils, it is sometimes cultivated as an ornamental plant in water gardens, rain gardens, and naturalistic landscapes.

Risks & Threats
Although Equisetum variegatum is not currently known to be naturalized in the Hawaiian Islands, it possesses traits that raise concern for tropical island ecosystems. Like other horsetails, it spreads aggressively through extensive underground rhizomes and can quickly form dense, persistent colonies that are difficult to remove. These traits allow it to outcompete other plants for space and resources, particularly in wet or disturbed habitats such as stream edges and wetlands. If introduced and established, variegated horsetail could potentially displace native vegetation, alter habitat structure, and become challenging to control due to its resilient root system and ability to regenerate from fragments. Because of these characteristics, planting this species is discouraged, and gardeners are encouraged to select non-invasive or native alternatives instead.

High Risk Traits:

• Elevation range exceeds 1000 m
  
• Weedy and difficult to remove
  
• A potential garden weed
  
• Related Equisetum species have become invasive
  
• Possibly toxic to cattle and other grazing animals
  
• Tolerates many soil types
  
• Forms monocultures within native range
  
• May hybridize with other Equisetum species
  
• Spread by spores and vegetatively by rhizomes
  
• Can resprout if only aboveground vegetative material is removed

Low Risk Traits:

• Thrives in temperate climates, so may only threaten higher elevation ecosystems in the tropics
  
• Unarmed (no spines, thorns, or burrs)
  
• Short-lived spores
  
• Herbicides may provide effective control