soursop

Oxalis pes-caprae
Herb
Basal
Compound
Yellow
Green

An almost hairless plant with long-stalked, trifoliate leaves that often have dark spots. Oxalis is often mistaken for clover. However, while they both can have a similar appearance with trifoliate sectioned leaves, oxalis is easily distinguishable by having heart-shaped leaves compared to the oval-shaped leaves of clover. 

Common names 
Also known as: Soursop, African wood sorrel, Bermuda buttercup, buttercup oxalis, Cape cowslip, Cape sorrel,
Family 
Oxalidaceae
Deciduous 
No
Flowering time 
May to November
Native/Exotic 
Exotic
Origin 
South America (Pink Flowering), Southern Africa (yellow flowering)
Notifiable 
No
State declaration 
Nil
Council declaration 
NIL - Reduce
Known distribution 

Widely naturalised, particularly in the southern parts of Australia. It is common in eastern and southern New South Wales, Victoria, Tasmania, south-eastern South Australia and south-western Western Australia. Also occasionally naturalised in south-eastern Queensland and the southern parts of the Northern Territory, as well as in other parts of New South Wales, South Australia and Western Australia.

Habitat 

This species is most commonly found in temperate regions, but occasionally also inhabits semi-arid and cooler sub-tropical environments. It is a weed of gardens, parks, lawns, waterways, roadsides, disturbed sites, waste areas, pastures, grasslands, open woodlands, crops and orchards.

Habit 

A long-lived (i.e. perennial) herbaceous plant with upright (i.e. erect) flowering stems usually growing 15-30 cm tall, but occasionally reaching up to 45 cm in height. It produces a rosette of leaves at ground level and underground stems (i.e. rhizomes), bulbs, bulbils and tubers. The aboveground stems and leaves are short-lived (i.e. annual) and die back each year.

Impact and control methods 

Soursob (Oxalis pes-caprae) is a significant environmental weed in Victoria and South Australia and an environmental weed in Western Australia and New South Wales.

Stem and leaves 

The leaves emerge from the top of an underground stem (i.e. rhizome) at or just below the soil surface. They are borne on long stalks (i.e. petioles) 5-22 cm long and consist of three heart-shaped (i.e. obcordate) leaflets. These leaflets (5-30 mm long and 4-35 mm wide) are mostly green in colour, sometimes bearing brown or purple-coloured markings, and fold downwards during darkness. They are hairless with entire margins and deeply-notched tips (i.e. emarginate apices).

Flowers and fruits 

The bright yellow flowers (25-40 mm across) are borne in loose clusters (each with 3-25 flowers) at the top of the stems on individual stalks (i.e. pedicels) up to 20 mm long. They are trumpet-shaped (i.e. tubular) in appearance with five broad overlapping petals (15-25 mm long) that are fused together towards their bases. These flowers also have five sepals, ten stamens and an ovary topped with five styles. They open only during sunny conditions and close again at night or during dull conditions. Flowering occurs mainly from early winter through to late spring (i.e. from May to November).

The short capsules are rarely formed in Australia.

Reproduction and dispersal 

This species most commonly reproduces via underground bulbs and bulbils (seeds are rarely produced in Australia). The cone-shaped (i.e. conical) bulbs are white, fleshy segments (8-30 mm long) covered in brown scales, while the bulbils are smaller and generally lack the brown covering of scales.

Bulbs and bulbils are most commonly spread by cultivation and other forms of soil movement. They are also dispersed to new areas in contaminated soil, in dumped garden waste, by water movement and by animals (e.g. birds).

Similar species 

There are approximaely 30 species of Oxalis in Australia