Oxalis species

These are weeds of South African origin that many of you will be familiar with in your bushland. They are soursob, fingerleaf and four o'clock. All belong to the genus Oxalis, in the family Oxalidaceae. Of the 800 species in the genus, 14 occur in Western Australia and only one, Oxalis perennans, is native.
Bulbous perennial herbs, the foliage of these three weeds forms dense mats over the ground from autumn to spring, inhibiting the germination of native species and out competing native herbs for space, light and nutrients.

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Soursob (Oxalis pes-caprae) was introduced in 1839 as a garden ornamental. Associated with mediterranean climates, it also occurs in sub-tropical and

semi-arid regions and is present in all states and territories.

Commonly seen in disturbed areas, the weed occurs on a range of soil types, however it is most prolific on heavier, well drained, fertile soils.

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Four o'clock (Oxalis purpurea) is a small low growing weed to 10cm high. The leaflets are almost circular, green to deep reddish green.

The leaves form a rosette above which, the short stemmed flowers appear. Three colour forms occur, purple, mauve and white. All have a yellow throat. The shallow bulb is large - up to 2cm across, smooth, rounded and black/brown.

O. purpurea is also thought to be a garden escapee. It prefers damp conditions and is widespread on heavier soils throughout the south-west of WA. Harder to kill than soursob, it has replaced this weed in agricultural areas.

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Finger leaf (Oxalis glabra) is a small erect plant to 15cm high. One or two five petaled pinkish purple flowers with yellow throats are produced on thin upright stems.

Short, narrow, green to reddish leaves occur in clusters along the stem length. The small bulbs have a brown papery cover.

O. glabra is widespread in disturbed woodlands around the Perth metropolitan area. The weed is common on heavy soils from Perth to York and has a scattered distribution in the lower south-west.