Monographs on invasive plants in Europe: Ageratina adenophora (Spreng.) R.M. King & H. Rob

Citation

Fried G, Datta A, Brundu G, Chapman D, Follak S, Frohlich D, Richardson DM, van Valkenburg J & Tanner R (2025) Monographs on invasive plants in Europe: Ageratina adenophora (Spreng.) R.M. King & H. Rob. Botany Letters. https://doi.org/10.1080/23818107.2025.2529890

Abstract
Ageratina adenophora (Spreng.) R.M. King & H. Rob. (Crofton weed) is a triploid, apomictic perennial herb or sub-shrub native to Mexico that is highly invasive in many parts of the world. This species thrives in diverse habitats, from wet forest margins to dry slopes and disturbed urban areas. Initially introduced globally as an ornamental plant, it has now naturalized across many continents, including Europe, Asia, Africa, Oceania, and the Americas, often displacing native flora and altering ecosystems. Its introduction to Europe dates back to the 19th century, with naturalization first recorded on the French Riviera. Ageratina adenophora is now established in several southern European countries (Portugal, Spain, France, Italy, Croatia, Greece) and across the Macaronesian islands. It spreads via wind- and water-dispersed seeds and can also propagate vegetatively, particularly along riparian systems and disturbed sites. Despite its prolific reproduction and adaptability, its expansion in Europe has so far remained moderate, possibly due to climatic limitations and unsuitable habitats. Ecologically, A. adenophora exhibits remarkable phenotypic plasticity and physiological adaptations that enable it to survive a range of abiotic stresses including cold, drought, and variable light levels. The species benefits from mutualisms with soil microbes and displays enhanced nitrogen-use efficiency in introduced ranges. Although initially valued for ornamental and medicinal purposes, A. adenophora is now widely recognized as a harmful invader. It invades both natural and semi-natural habitats and has demonstrated a capacity to alter soil chemistry, suppress native vegetation through competition and allelopathy, and host diverse pathogens and endophytes. Ageratina adenophora negatively impacts biodiversity, ecosystem functioning, and agriculture by forming dense, monospecific stands and disrupting native communities. Its presence in biodiversity hotspots and protected areas—such as Himalaya, South Africa, and the Canary Islands—poses significant conservation challenges. Control efforts, including the use of biological agents such as Procecidochares utilis Stone 1947, have yielded mixed results. The most effective method for small areas is to physically remove A. adenophora before it sets seed. This can be done by hand-pulling or cutting. Given the continued spread and resilience of this species there is an urgent need for coordinated management strategies and increased awareness, especially in the face of climate change which may further facilitate its expansion in Europe and beyond.

Keywords
Asteraceae; biological invasions; Eupatorieae; plant invasions; phenotypic plasticity

Journal
Botany Letters