Perennial herb with bulbils, sour-tasting stalks, clover-like leaves and yellow flowers.
Scientific name: Oxalis pes-caprae L.
Common names: bermuda buttercup, buttercup oxalis, soursob
Status in Portugal: invasive species (listed in Decreto-Lei nº 92/2019)
Risk Assessment score: 24 | 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.
Last update: 11/07/2021
How to recognise it
Flowering: January to April.
Oxalis corniculata L. (creeping woodsorrel), also with a yellow flower, has some similarity but has aerial stems that are well developed, so they cannot be confused.
Characteristics that aid invasion
It propagates vegetatively, by bulbils. Oxalis pes-caprae produces many bulbils that fragment easily and are the main mean of dispersion.
It rapidly augments its distribution originating extensive areas where it dominates.
Native distribution area
South Africa (Cape region).
Distribution in Portugal
Mainland Portugal (all provinces), Azores archipelago (all islands), Madeira archipelago (Madeira and Porto Santo islands).
Geographic areas where there are records of Oxalis pes-caprae
Other places where the species is invasive
Mediterranean Europe, western USA (California), Asia, South Africa, New Zealand, Australia, South America.
Probably for ornamental purposes.
Preferential invasion environments
Crop lands and wastelands, mainly in silted soils.
It doesn’t tolerate frost and low temperatures very well, ending up by drying the aerial part in those conditions.
Impacts on ecossystems
It forms dense mats that may inhibit the development of native vegetation.
It reduces productivity in crop fields.
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 Oxalis pes-caprae include:
Hand pulling (preferencial methodology): It is applied to plants of all sizes. In more compacted substrates, hand pulling must be made during the rainy as to facilitate the removal of the bulbils. As much as possible, it should be guaranteed that there are no bulbils left in the ground so that there may not be a reinvasion. Frequent hand pulling should be done, before there is time for new bulbils to form, so the plant ends up weakening.
Soil Solarisation. It’s an alternative to hand pulling, mainly in extensive areas that are invaded by the species. It should be guaranteed that no native species are affected.
Foliar application of herbicide. spray with herbicide (active substance: glyphosate) limiting its application to the target species. The herbicide application should be done before flowering.
Visit the webpage How to Control for additional and more detailed information about the correct application of these methodologies.
Dufour-Dror J-M (2012) Alien invasive plants in Israel. The Middle East Nature Conservation Promotion Association, Ahva, Jerusalem, 213pp.
Gallo AG, Delgado OR, Fernandes FM, Silva L (2008) Oxalis pes-caprae L. In: Silva L, Land EO, Luengo JLR (eds) Flora e fauna terrestre invasora na Macaronésia. Top 100 nos Açores, Madeira e Canárias. Arena, Ponta Delgada, pp. 268-270.
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.
USDA, NRCS. (2012) The PLANTS Database. National Plant Data Team, Greensboro, NC 27401-4901 USA. Available: http://plants.usda.gov [Retrieved 10/11/2012].