In mainland Portugal, over the last two centuries, and especially in more recent decades, the number of exotic species (including casual, naturalized and invasive) has increased significantly, currently amounting to about 670 species*, which corresponds to approximately 18% of the total native flora (Almeida and Freitas 2012). In the archipelagos of Madeira and the Azores the number of exotic species is also very high. For the Madeira and Savage Island archipelagos 430 exotic species have been recorded, equivalent to approximately 43% of all the vascular plants in these archipeligos (Jardim and Sequeira 2008). In the Azores, of the approximately 1000 species of vascular plants, around 60% are exotic (Scott and Smith 2006).
Several of the exotic species listed in Portugal are considered invasive (in mainland Portugal approximately 8% of the exotic species have invasive behaviour), posing a serious threat to the ecosystems.
In 1999, Portuguese legislation recognized the gravity of the problem in the Decreto-Lei nº. 565/99, of 21 December, which regulated the introduction of non-native (exotic) species. In 2019 a new diploma replaced the previous - Decreto-Lei nº 92/2019 - considering over 200 exotic plant species in Portugal as invasive. Furthermore, the legislation prohibits the possession, cultivation, growing and the trade of species that are considered invasive or of ecological risk and limits the introduction of new species in hte national territory (with some exceptions).
For the species that demonstrate invasive behaviour in mainland Portugal, Madeira** and the Azores**, please consult our Species Fact Sheets (some Fact Sheets still under development). These have detailed information about the species’ characteristics, distribution, impact and possible methods of controlling them. The species presented are grouped by their growth form – trees and shrubs, grasses and herbs, aquatic grasses, succulents and climbing plants. This classification may not be immediately obvious, such as in the case of the American Pokeweed (Phytolacca americana). This plant may look like a shrub but in botanical terms it is a herb.
* these numbers include exotic species that are considered by these authors as being more or less naturalised. Many of the cultivated species that appear exclusively in gardens or on agricultural land are not included.
** at present, for the species common to the archipelagos and to the mainland, it is only possible to consider the most problematic species. Other species may be included where there is relevant information at a later stage.
Almeida J, Freitas H (2012) Exotic flora of continental Portugal – a new assessment. Bocconea 24: 231-237.
Almeida J (1999). Flora exótica subespontânea de Portugal continental (plantas vasculares). Catálogo das plantas vasculares exóticas que ocorrem subespontâneas em Portugal continental e compilação de informações sobre estas plantas. Master thesis, University of Coimbra, Coimbra.
Jardim R, Sequeira M (2008) As plantas vasculares (Pteridophyta e Spermatophyta) dos arquipélagos da Madeira e das Selvagens. In: Borges PAV, Abreu C, Aguiar AMF, Carvalho P, Jardim R, Melo I, Oliveira P, Sérgio C, Serrano ARM, Vieira P (eds) A list of the terrestrial fungi, flora and fauna of Madeira and Selvagens archipelagos. pp. 157-178, Direcção Regional do Ambiente da Madeira and Universidade dos Açores, Funchal and Angra do Heroísmo.
Marchante H (2011) Invasion of Portuguese dunes by Acacia longifolia: present status and perspectives for the future. Faculdade de Ciências e Tecnologia. Universidade de Coimbra. Doutoramento em Biologia, especialidade em Ecologia. 184pp.
Marchante H, Morais M, Freitas H, Marchante, E (2014). Guia Prático para a Identificação de Plantas Invasoras em Portugal. Coimbra: Imprensa da Universidade de Coimbra. 208pp.
Silva L, Smith C (2006) A quantitative approach to the study of non-indigenous plants: an example from the Azores Archipelago. Biodiversity and Conservation 15(5): 1661-1679.