Oxalis (Oxalis corniculata, O. latifolia & O. pes-caprae)

Oxalis pes-caprae Photo: (c) Harry Rose CC BY 2.0

Family: Oxalidaceae

Oxalis is a group of weeds found in most home gardens and waste areas. It is a rosette plant with trifoliate leaves borne on long petioles that superficially look like clover. However Oxalis leaves are more or less heart-shaped or notched, and often appear to be folded along the bid-rip. The flowers are distinctive and can help distinguish between the 10 Oxalis species that occur in Tasmania, including four native species.

The native O. magellanica has white flowers; the native O. exilis and O. perennans and the introduced O. corniculata have yellow flowers. O. pes-caprae has bright yellow flowers; O. latifolia has pinkish-purple flowers. O. incarnata has very pale pink-mauve flowers; O. purpurea has reddish-purple flowers. The native O. radicosa and the introduced O. articulata have bright pink-purple flowers.

Three different species are described in more detailed blow.

Soursob: Oxalis pes-caprae  – photo above

Growth Habit: Oxalis pes-caprae is a very invasive plant that produces a main tuber-like root, plus several small bulbs. It has trifoliate heart-shaped leaves with brown or purple spots on top. It occurs widely throughout the cooler regions of Australia.

Soursob is distinguished from Yellow Woodsorrel (O. corniculata) by its bright yellow flowers, generally brighter green leaves, more upright habit, and rhizomes rather than above ground stolons. It is distinguished from other Oxalis species by the combination of bulbs/tubers, and yellow flowers present as an umbel rather than solitary.

Type of Plant: Winter or spring growing biennial plant.

Photo: (c) Zachi Evenor

Flowers: A yellow trumpet shaped flower which grows in groups of 3-16.

Dispersal: Soursob primarily reproduces from the bulbs, which may be spread by any soil movement.

Distribution: Grows in cultivated areas, waste and recreational and is very common as a garden weed.

Status: Declared a Secondary weed in Tasmania.

Weed Impact:

  • A major garden weed in most areas.
  • Extremely difficult to control once well established.
  • May cause oxalate poisoning in livestock if eaten.

For further information contact the Department of Primary Industry, Parks, Water and Environment, Tasmania.

Oxalis latifolia Photo: (c) Franz Xaver CC BY-SA 4.0

Fishtail Oxalis: Oxalis latifolia

Growth Habit: A low growing, bushy plant which produces many underground bulbs. It is far more invasive than O. corniculata and is commonly found in gardens and potted plants.

Type of Plant: A perennial, bulbous herb.

Photo: (c) John Tann CC BY 2.0

Flowers: Sometimes known as the pink shamrock, the flower is pink or purplish in colour with a diameter of 10-12 mm. This five petalled flower grows in groups of 12.

Dispersal: Main reproduction is by the bulbs, which are easily dispersed by any soil movement. Physical removal of the plant usually leaves several of the small bulbs behind, making the plant very difficult to eradicate.

Distribution: Found in most states, it prefers growing in cultivated soil.

Status: Declared a Secondary weed in Tasmania.

Weed Impact:

  • A major garden weed in most areas.
  • Extremely difficult to control once well established.
  • May cause oxalate poisoning in livestock if eaten.

Oxalis corniculata Photo: (c) Gail Hampshire CC BY 2.0

Yellow Wood Sorrel: Oxalis corniculata

Growth Habit: O. corniculata is the smallest of the three Oxalis species described here. Leaves are about 15 mm in diameter. Unlike the other species of introduced Oxalis, it does not produce bulbs, tubers or stout fleshy rhizomes. It is distinguished from the native O. incarnata by its yellow rather than white flowers.

Type of Plant: O. corniculata is an annual or short-lived perennial.

Photo: (c) Jason Hollinger CC BY 2.0

Flowers: The yellow flowers which are approximately 6 – 10 mm in diameter have five petals and number 1-6 per stem. This plant flowers most of the year.

Fruit/Seed: Seeds are about 1-1.3 mm long and 1 mm wide.

Dispersal: Seeds are readily spread by soil and water movement, and may also be scattered by machinery such as lawn mowers. It can root from the stems, but seed it the main means of spread.

Distribution: Found in all Australian states in grassy and waste areas. It is commonly found in home lawns, where it assumes a creeping habit.

Status: Declared a Secondary weed in Tasmania.

Weed Impact:

  • May invade lawns and displace desirable grasses.
  • May cause oxalate poisoning in livestock if eaten.

Control Methods:

  • Grubbing (all year). Remove entire plant including bulbs. Due to the numerous small bulbs, this can be a very tedious task.
  • Mulching (all year). Heavy mulching will suppress Oxalis.
  • Herbicide (summer, spring and autumn). Herbicides registered in Tasmania include glyphosate, metsulfuron and dicamba.

N.B. Always check the herbicide label before use.