Invasiveness Assessment - Soursob (Oxalis pes-caprae) in Victoria
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Plant invasiveness is determined by evaluating a plant’s biological and ecological characteristics against criteria that encompass establishment requirements, growth rate and competitive ability, methods of reproduction, and dispersal mechanisms.
| Each characteristic, or criterion, is assessed against a list of intensity ratings. Depending upon information found, a rating of Low, Medium Low, Medium High or High is assigned to that criterion. Where no data is available to answer a criterion, a rating of medium (M) is applied. A description of the invasiveness criteria and intensity ratings used in this process can be viewed here. |
The following table provides information on the invasiveness of Soursob.
A more detailed description of the methodology of the Victorian Weed Risk Assessment (WRA) method can be viewed below:
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Common Name: Soursob
Scientific name: Oxalis pes-caprae
| Question | Comments | Reference | Rating |
| Establishment | |||
| Germination requirements? | Most bulbs germinate after autumn rains. | P & C (1992) | MH |
| Establishment requirements? | Can establish under moderate canopy - occurs in olive, citrus and vineyards, as well as woodlands. | Pierce (1997) Carr et al (1992) | MH |
| How much disturbance is required? | Establishes in minor disturbed natural ecosystems, (See Car et al 1992), as well as vigorously growing crops (e.g. cereal) and pastures. | Carr et al (1992) P & C (1992) | MH |
| Growth/Competitive | |||
| Life form? | Erect perennial: geophyte. | P & C (1992) | ML |
| Allelopathic properties? | None described. |  | L |
| Tolerates herb pressure? | “Owing to a high oxalic acid content – the cause of the sour taste – soursob is not eaten readily by stock”. | Meadly (1965) | MH |
| Normal growth rate? | Its rapid growth rate is a key feature of the plant's competitiveness. | P & C (1992) | H |
| Stress tolerance to frost, drought, w/logg, sal. etc? | Tolerant of frost, water logging (infests drainage ditches), drought (occurs in semi arid parts of Morocco). | P & C (1992) Hildreth & Agamalian (1985) – Tanji (1994) | MH |
| Reproduction | |||
| Reproductive system | Reproducing from bulbs and bulbils. Viable seed is produced on some plants in Western Australia. | P & C (1992) | H |
| Number of propagules produced? | 20 flowers per plant x 3/5 seeds per flower = 60/100 seeds per plant. (estimate using illustrations). Seeds not commonly produced in Victoria. (DCFL 1987, Pierce). | Meadley (1965) | ML |
| Propagule longevity? | ? | | M |
| Reproductive period? | Forms dense monocultures. (See picture P & C (1992) p. 532). | P & C (1992) | H |
| Time to reproductive maturity? | “Plants arising from bulbils produce bulbs in their first year but do not flower”. So flower in second year. | P & C (1992) | MH |
| Dispersal | |||
| Number of mechanisms? | Bulbs/bulbils-machinery, water movement, birds eat bulbs. | P & C (1992) | H |
| How far do they disperse? | Ejection of seeds up to 2 m from the parent plant. “Because they are light. Clark (1934) considers that wind plays a major role. Bulbs float on water so this would be significant, particularly in Western Australia where Oxalis pes-caprae is associated with some major rivers and drainage systems”. (Pierce 1997). Above mechanisms could transport many seeds/bulbs > 200 m. | Pierce (1997) | H |
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© The State of Victoria, 1996 - 2009.
This document was last reviewed on 18/08/2009