Galenia pubescens in the EPPO region: addition to the EPPO Alert List
Why
Galenia pubescens is a perennial woody herb native to South Africa. The species currently has a limited distribution in the EPPO region where it is present in Israel and Spain. G. pubescens has invaded coastal sand dunes in Spain where the species can form dense monocultures which have a negative impact on local biodiversity.
Geographical distribution
EPPO region: Israel (Sharon Plain – rare; Negev Highlands – very rare), Spain.
Africa: South Africa (Eastern Cape, Free State, North West, Northern Cape, Transvaal, Western Cape).
North America: USA (California).
South America: Chile (Central).
Oceania: Australia.
Morphology
Galenia pubescens is a prostrate to decumbent semi woody perennial herb. The stem is cylindrical up to 1.5 mm in diameter. Leaves are ovate to spatulate and up to 35 mm in length and 15 mm wide. The inflorescence is a leafy cyme with axillary flowers. Flowers are bisexual, radial and approximately 4-5 mm wide. Flower colour is either pink or whitish pink. Seeds are contained in capsules 3 mm in length. Seeds are 1-2 mm in length, shiny and black. The plant is mat forming. In Australia, the plant can grow up to 60 cm in height and 1.6 m wide. G. pubescens has an extensive tap root that can reach depths of 2 m (Hartmann, 2002).
Biology and ecology
Galenia pubescens is an opportunistic species colonising highly disturbed ground (García-de-Lomas et al., 2010) which can outcompete native plant species. In Spain the species forms dense prostrate mats in wetlands and dunes. García-de-Lomas et al., (2010) showed that G. pubescens will flower throughout the year with maximum flower density recorded in spring. Annual seed production was estimated between 95 300 and 100 200 seeds per m2. In Israel, G. pubescens flowers in March, April and May. Bees seem to be attracted to G. pubescens, however, even though it may be a good nectar source, honey produced by this species is recorded as being foul tasting (Geelong Beekeepers Club Inc, 2015).
Habitats
In South Africa, G. pubescens colonises inland locations with karoo vegetation, and coastal areas at altitudes of 15-1 830 m a.s.l (Arnold and De Wet, 1993). In Australia, G. pubescens is present in semi-arid and sub-tropical environments where it is commonly found in highly disturbed sites such as mines, waste areas, coastal regions, roadsides, parks, footpaths and lawns. In southern Spain, G. pubescens is invasive in the Cadiz Bay Natural Park where it invades coastal areas and salty wetlands (García-de-Lomas et al., 2010). The species is also found growing along road edges and other disturbed habitats (García-de-Lomas et al., 2009). In Australia, G. pubescens is found growing in coastal regions, pasture land and grasslands.
Pathways for movement
Galenia pubescens spreads naturally by seed. Seeds are small and can be blown short distances on wind currents. As the species grows in coastal regions further natural spread may be facilitated by wave and sand movement. Additionally, the plant may be spread by livestock that ingest the seeds. Spread may be facilitated by transport of machinery, i.e. mowers or vehicles tyres.
Impacts
Galenia pubescens has been shown to decrease native species richness and diversity in invaded plots in Spain (García-de-Lomas et al., 2010). Plant functional types were significantly altered in invaded plots where perennial species were replaced by annual ruderal grasses or forbs (García -de-Lomas et al., 2010). The change in plant species composition within invaded stands can act to alter the structural composition of vegetation which can have an impact on ecosystem services. García-de-Lomas et al. (2010) suggests that increased soil humidity, plant litter accumulation and soil nutrient composition may all be altered as a result of dense mats of G. pubescens. Shading caused by mat formation may modify germination requirements for native plant species and thus prevent restoration of native plant community. By stabilizing sand dunes, G. pubescens alters the natural disturbance regimes of these habitats. Stabilization can enhance the persistence of the invasive population and the establishment of new populations (D’Antonio and Meyerson, 2002). There is some evidence that G. pubescens is toxic to domesticated animals. The plant can produce high levels of nitrates and oxalates that can cause death in animals when eaten (Williams, 1979).
Control
Mechanical removal and follow-up spraying is the most effective way to control and manage invasive populations of G. pubescens. Control trials in Southern Spain using glyphosate spraying have shown a high efficiency against G. pubescens.
Sources
Arnold TH, De Wet BC (1993) Plants of Southern Africa: Names and Distribution. Memoirs of the Botanical survey of South Africa No. 62. National Botanical Institute, Pretoria.
D’Antonio CM, Meyerson LA (2002) Exotic Plant Species as Problems and Solutions in Ecological Restoration: A Synthesis. Restoration Ecology 10, 703–13.
García-de-Lomas J, Hernández I, Sanchez-García I (2009) Incipient Invasion of Galenia secunda Sond. (Aizoaceae) in Southern Spain. Biological Invasions 11, 467–472.
García-de-Lomas J, Cózar A, Dana ED, Hernández I, Sanchez-García I, García CM (2010) Invasiveness of Galenia pubescens (Aizoaceae): A New Threat to Mediterranean-Climate Coastal Ecosystems. Acta Oecologica 36, 39–45.
Geelong Beekeepers Club Inc. (2015) Flora: Weeds Galenia pubescens. http://geelongbeekeepersclub.org/wp-content/uploads/2015/01/Weed-Galenia-pubescens-photos.pdf.
Hartmann HEK (2002) Illustrated Handbook of Succulent Plants: Aizoaceae A-E. Berlin Heidelberg: Springer-Verlag.
Williams MC (1979) Toxicological Investigations on Galenia pubescens. Weed Science 27(5), 506–508.