Ambrosia psilostachya and Xanthium spinosum: addition to the EPPO List of Invasive Alien Plants
In May 2026, the EPPO Panel on Invasive Alien Plants prioritised two widespread alien species using the Standard PM 5/6 EPPO prioritization process for invasive alien plants. The Panel agreed both species should be included on the EPPO List of Invasive Alien Plants.
Ambrosia psilostachya (Asteraceae)
Ambrosia psilostachya is native to North America and widespread in the EPPO region. Ambrosia psilostachya spreads naturally by both seed and rhizomes. Seed is wind dispersed and can become incorporated into the water body. Plant propagules have been shown to travel over distances of up to 170 km from and to coastal dunes by sea currents. In the EPPO region A. psilostachya can have negative impacts on biodiversity and ecosystem services. Currently, A. psilostachya is not a common species in agricultural systems in the EPPO region. However, with habitat and land use change, and with the effect of climate change, there may be the potential for establishment and impact in agricultural systems.
Xanthium spinosum (Asteraceae)
Xanthium spinosum is native to the Americas and is established in more than 20 EPPO countries. It spreads via seed which can be dispersed from the parent plant by water (moving along the water body) and by animals and human activity. X. spinosum can grow in a variety of different habitats where it can have negative impacts on biodiversity and ecosystem services. Studies have shown that with the increase of percentage cover of X. spinosum, native plant species and community stability decrease.
Sources
EPPO Panel on Invasive Alien Plants (2026-05).
EPPO (2012) PM 5/6 EPPO prioritization process for invasive alien plants. EPPO Bulletin 42, 463-474. https://doi.org/10.1111/epp.2592