Evergreen shrub or small tree, with robust and very sharp needle-like leaves.
Scientific name: Hakea sericea Schrader
Common name: silky hakea
Status in Portugal: invasive species (listed in the annex I of Decreto-Lei n° 565/99, of 21 December)
Risk Assessment score: (in development)
Synonymy: Hakea acicularis (Sm. ex Vent.) Knight, Hakea acicularis (Vent.) R. Br., Hakea tenuifolia (Salisb.) Domin.
Last update: 01/07/2014
How to recognise it
Shrub or small tree up to 4 m, with an irregular canopy.
Leaves: evergreen, in the shape of a needle of 0,5-1,5 mm diameter, very robust, of 4-8 cm, extremely sharp, dark green to greyish-green.
Flowering: January to April.
There are other Hakea species that are relatively similar, also spiny (Hakea gibbosa Cav.,for example), but haven’t been yet referred in Portugal.
Characteristics that aid invasion
It reproduces by seed. Frequently, the seeds remains enclosed within the fruits, which in their turn remain grasped to the tree, throughout the plants’ lifetime. They are released when the tree is burned or dies. The seeds are then projected to great distances, creating new invasion foci that frequently occupy very extensive areas.
Native distribution area
Distribution in Portugal
Mainland Portugal (Trás-os-Montes, Minho, Douro Litoral, Beira Baixa, Beira Litoral, Estremadura, Ribatejo, Baixo Alentejo, Algarve).
Other places where the species is invasive
Europe (Spain), South Africa, New Zealand.
For ornamental purposes and to form protection hedges.
Preferential invasion environments
Disturbed areas, like roadsides. It also invades (semi)natural areas, where it is increasingly frequent.
It occurs in large extensions, in high densities, frequently in the sequence of fires that burn specific individuals/hedges.
It is resistant to wind and drought.
Impacts on ecossystems
It forms dense, impenetrable stands inhibiting the development of native vegetation, affecting the wildlife, reducing the amount of available water and enhancing the probability of fire occurrence.
Expensive control methods.
The prickly leaves may injure both humans and cattle, inhibiting the presence of animals and creating difficulty in control operations.
Natura 2000 Network habitats more subject to impacts
– European dry heaths (4030);
– Thermo-Mediterranean and pre-desert scrub (5330).
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 Hakea sericea 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.
Cutting: preferential methodology for young and adult plants. Cut the trunk as close to the ground as possible by using manual and/or mechanical equipment. It should be done before seed maturation. After cutting, the cut plants should be left to dry for 12-18 months until they release the seeds and these begin to germinate. After, the remaining biomass should be burned, leading to the seed’s and seedling’s death. Alternatively, this biomass may be destroyed.
It is an effective methodology, but expensive and with negative consequences for the native vegetation, if it still exists alongside the invaded areas.
Foliar application of herbicide: over recent sprouts (25-50 cm tall) or when high germination rates occur. Spray with herbicide (active substance: triclopyr) limiting as much as possible its application to the target species.
In South Africa good results have been achieved with two agents: Erytenna consputa Pascoe (Coleoptera: Curculionidae), a weevil that feeds off the seeds; Carposina autologa Meyrick (Lepidoptera: Carposinidae), that also destroys the seeds.
These agents have not yet been tested in Portugal as to verify its safety relatively to native species, so its use has not yet constituted an alternative in our country.
Visit the webpage How to Control for additional and more detailed information about the correct application of these methodologies.
Agricultural Research Council – Plant Protection Research Institute – Weed Research Division (2014) Management of invasive alien plants: A list of biocontrol agents released against invasive alien plants in South Africa. Available: http://www.arc.agric.za/arc-ppri/Documents/WebAgentsreleased.pdf [Retrieved 03/03/2014].
Gordon AJ (1999) A review of established and new insect agents for the biological control of Hakea sericea Schrader (Proteaceae) in South Africa. African Entomology. Memoir n°1: 35-43.
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.
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