First report of Amaranthus tuberculatus in Portugal
Amaranthus tuberculatus (Amaranthaceae - EPPO A2 List) is an annual dioecious non-native species to the EPPO region with transient and established occurrences known in a number of EPPO countries. In the EPPO region, A. tuberculatus grows mainly in ruderal sites and along riverbanks, and to a lesser extent in crop fields. During recent fieldwork in Portugal, several populations of A. tuberculatus were found along the banks of the River Tagus, upstream of Porto de Muge (parish of Valada, region of Oeste e Vale do Tejo). A. tuberculatus was found at numerous locations, between Azambuja and Azinhaga, over a distance of approximately 60 km. The further upstream, the more numerous the A. tuberculatus plants were. Near Azinhaga, A. tuberculatus grows abundantly along the lower stretch of the Almonda River, a tributary of the Tagus. At all locations, A. tuberculatus was found growing on sand and gravel riverbanks. Both male and female plants were found and the total population is estimated to be in the tens of thousands of individuals. Currently, A. tuberculatus was not found in the extensive agricultural areas which border the Tagus river. However, if a similar spread is seen in Portugal as in other countries (e.g. Italy), A. tuberculatus could cause economic damage to this area.
Sources
Verloove F (2026) The North American weed Amaranthus tuberculatus (Amaranthaceae) new to Portugal: previously overlooked or spreading rapidly? Acta Botanica Croatica, DOI: 10.37427/botcro-2026-010