McCulloch-Jones EJ, Crouch N, Kraaij T (2023) Early detection of alien fern species through the consultation of horticultural catalogues. Management of Biological Invasions 14(1): 45–62, https://doi.org/10.3391/mbi.2023.14.1.02

Horticultural trade is a well-documented pathway of introduction for numerous invasive species globally, including ferns. In this study, we analysed trade in terrestrial true ferns (Polypodiophyta) in selected anglophone countries: Canada, the United States of America, the United Kingdom and the Republic of Ireland, South Africa, Australia, and New Zealand. The study provides an overview of fern trade and explored the relationship between trade and alien fern introductions with a view to prioritise risk assessment and ultimately inform management interventions. Through consulting horticultural catalogues, in a period of just six months we identified a total of 382 fern species currently traded by 148 traders. International trade was observed in only three countries with most trade occurring at national scales and e-commerce did not clearly dominate over on-ground trade. Alien species accounted for more than 60% of the total number of traded species in most countries except in Australia and New Zealand. A total of 193 species have not previously been recorded as alien in plant species inventories in their countries of trade and were assigned the status of introduced. Several species (2–10 species per country; 38 species in total) known to be invasive in their country of trade remain actively traded there and are immediate priorities for regulation pending climate, risk and impact assessments. We categorised another 78 species with the status of naturalised or introduced in their trade countries in terms of their priority for risk or climate suitability assessment, and identified 101 potential candidates (approximately 20% of alien species traded per country) for Safe listing. This research constitutes one of few studies that have used horticultural catalogues to identify alien species, and highlights the efficiency of this approach as a tool for the early detection and prioritisation of potentially invasive species for management responses.