Small evergreen tree, with light green leaves and pale yellow spherical flower heads.
Scientific name: Acacia retinodes Schlecht.
Common name: water wattle
Family: Fabaceae (Leguminosae)
Status in Portugal: invasive species (listed in the Decreto-Lei nº 92/2019, 10 july)
Risk Assessment score: 17| Value obtained according to a protocol adapted from the Australian Weed Risk Assessment (Pheloung et al. 1999), by Morais et al. (2017), according to which values above 13 mean that the species has risk of having invasive behavior in the Portuguese territory | Updated on 30/09/2017.
Synonymy: Acacia floribunda auct., non Willd., Acacia fragrans Pottier, Acacia longissima Chopinet, Acacia provincialis A. Camus, Acacia retinodes Schldl. var. floribunda H.Vilm., Acacia retinoide Schltr., Acacia retinoides Schltr., Acacia rhetinoides Schltr., Acacia rostellifera sensu auct., Acacia. semperflorens A. Berger
Data de atualização: 01/07/2021
How to recognise it
Shrub or tree up to 8 m, with a smooth grey rhytidome.
Leaves: evergreen, reduced to light green phyllodes, of 3-20 x 0,2-1,5 cm, with an only longitudinal vein.
Flowers: pale yellow arranged in globular flower heads of 0,5-0,8 cm cm diameter, which in turn are arranged (6-15) in racemes.
Fruits: compressed light brown pods, almost linear; seeds completely encircled by a rose/scarlet funicle.
Flowering: of the Acacia species in Portugal, it is one of the few that can flower more than once a year. However, flowering occurs preferentially in the months of April and May.
Acacia saligna (Port Jackson wattle) is relatively similar, but its phyllodes are wider (0,5-5 cm) and bluish; the flower heads are bright yellow and with a larger diameter and the funicle is whitish and smaller than the seed. There are other species of Acacia that can be eventually confused with A. retinodes, but they have phyllodes with more than one longitudinal vein.
Characteristics that aid invasion
It reproduces by seed, producing many seeds that remain viable in the ground for many years.
Native distribution area
Distribution in Portugal
Mainland Portugal (Minho, Douro Litoral, Beira Litoral, Estremadura, Alto Alentejo, Baixo Alentejo, Algarve).
Geographic areas where there are records of Acacia retinodes
Other places where the species is invasive
Europe (Spain, Italy), some parts of Australia (Victoria).
For ornamental purposes.
Preferential invasion environments
Disturbed areas and roadsides, sometimes appearing on coastal dunes.
Impacts on ecossystems
It forms very dense populations inhibiting the development of native vegetation. In Portugal, it is not one of the most dispersed species, being known few (when compared with A. dealbata, A. melanoxylon or A. longifolia) situations where these levels of impact are verified.
It produces a lot of nitrogen-rich litter, which promotes soil change.
It has potential expensive control measures.
Natura 2000 Network habitats more subject to impacts
– Wooded dunes with Pinus pinea and/or Pinus pinaster (2270).
Controlling an invasive species demands a well-planned management, which includes the determination of the invaded area, identifying the causes of invasion, assessing the impacts, defining the intervention priorities, selecting the adequate control methodologies and their application. Afterwards it is fundamental to monitor the efficiency of the methodologies and recuperation of the intervened area as to perform, whenever necessary, the follow-up control.
The control methodologies used for Acacia retinodes include:
Hand pulling: preferential methodology for seedlings and small plants. When in more compacted substrates, hand pulling must be made during the rainy season as to facilitate the removal of the root system. It should be guaranteed that no stumps and main roots are left in the ground.
Physical + chemical control
Cut stump method: Apply to adult plants. Cut the trunk as close to the ground as possible and immediately (in the following seconds) apply herbicide (active substance: glyphosate) to the cut stump. If shoots should latter on appear, these should be immediately eliminated through cutting, pulling or foliar application of herbicide (active substance: glyphosate); up to 25 to 50 cm high. Shoots of larger dimensions (from 2-3 cm diameter) may be ring-barked or else should be repeated the initial methodology (cut stump method).
Foliar application of herbicide: over recent sprouts (25-50 cm tall) or when high germination rates occur. Spray with herbicide (active substance: glyphosate) limiting as much as possible its application to the target species.
It may be strategically used to favour germination of the seed bank, e.g., after the control of adult individuals (with the adequate management of the resulting biomass) and the subsequent elimination of seedlings. This method provides an advantageous reduction of the seed bank, both by destroying part of the seeds or by stimulating the germination of the remainders.
Visit the webpage How to Control for additional and more detailed information about the correct application of these methodologies.
Marchante E, Freitas H, Marchante H (2008) Guia prático para a identificação de plantas invasoras de Portugal Continental. Imprensa da Universidade de Coimbra, Coimbra, 183pp.
Starr F, Starr K, Loope L (2003) Acacia retinodes. Available: http://www.hear.org/starr/hiplants/reports/pdf/acacia_retinodes.pdf [Retrieved: 06/11/2012].