Tree ferns on the move: patterns of movement and current introduction status of Cyatheales species around the world

Abstract Tree ferns (order Cyatheales) have been moved from their native ranges for more than two centuries, and the number of species introduced to new countries has recently increased rapidly. However, no comprehensive global list of alien tree ferns exists. Botanical garden collections and the Global Biodiversity Information Facility database were examined, and a systematic literature review was conducted to collect information on tree fern introduction dates, locations and impacts in non-native ranges. Overall, 158 species out of 795 Cyatheales species (c. 20%) were found to have been introduced. The earliest documented introduction occurred in 1789 when Dicksonia arborescens L’Hér. was moved from St Helena Island to the United Kingdom. Tree fern introductions are biased in favour of well-developed countries with historical exploration in regions with rich native tree fern floras. Five species have naturalised ( Alsophila australis in Sri Lanka; Alsophila speciosa in Madagascar; Sphaeropteris excelsa in the United States of America; Sphaeropteris medullaris in Madeira (Portugal); and Lophosoria quadripinnata in Fiji, French Polynesia and the United States of America). Two species are invasive: Sphaeropteris cooperi in the Azores (Portugal), Hawaiian Is. (USA), Mauritius, Réunion Isl. (France) and South Africa; and Dicksonia antarctica in the Azores (Portugal) and Sri Lanka. The extensive history of tree-fern movement has radically altered the global distribution of the order Cyatheales, creating substantial invasion debt. The 151 alien (not yet naturalised) species represent a substantial capacity for future invasion. This list can inform monitoring of the distribution of already introduced species to support prevention of further invasions.