Synonyms - Oxalis violacea is often incorrectly identified as Oxalis latifolia.
Family: - Oxalidaceae.
Names:
Oxalis is from the Greek oksos meaning sour and refers to the taste of the leaves and stems.
Latifolia is from the Latin latus meaning broad and folius meaning leaf and refers to the leaflets which are more squat than in related species.
Fishtail Oxalis refers to the fishtail shape of the leaflets and its membership of the Oxalis genus.
Other names:
Fish-tailed Oxalis
Oxalis
Oseille (Mauritius)
Pink Shamrock
Ranksuring (South Africa)
Trefle (Mauritius).
Summary:
A low growing, shrubby, clover leaved annual or perennial plant with pink purple flowers.
Description:
Cotyledons:
Two.
Leaves:
Arise from fleshy leaf bases that form a bulb. Trifoliate. 30-50 mm diameter. Margins and under surface may be hairy.
Stipules - Small, round , joined to petiole.
Petiole - Long, slender, erect, 100-250 mm long.
Blade - Of leaflets, 15-30 mm long by 30-60 mm wide, divided into two lobes or deeply notched, triangular in outline. Base tapered. Surface hairless. Fold up along the midrib at night and on dull days.
Stems:
No aerial stem. Underground stems or stolons 50-100 mm long may form and produce 5-6 mm bulbils at their tips.
Flower head:
On stalks (peduncles) 150-300 mm long, longer than petioles, with clusters of 5-12 flowers on shorter stalks (pedicels), 12 mm long, that are initially erect and droop with age.
Flowers:
The trumpet shaped, purple and yellow, sterile flowers.
Ovary - Many celled.
Sepals - 5, shorter than petals, 2 small orange glands at the top.
Petals - Trumpet shaped with 5 lobes, greenish yellow on the outside and pinkish purple on the inside, 10-20 mm long by 15-20 mm diameter.
Stamens - 10 in 2 rings. Outer ones shorter and opposite the petals. Filaments joined at the base.
Anthers - Release pollen by a longitudinal slit.
Fruit:
Capsule.
Seeds:
None produced in Australia.
Roots:
White, waxy, carrot like, contractile taproot at the base of a white, waxy, 5-10 mm diameter bulb. Underground stoloniferous stems produce bulbils, 5-6 mm diameter at their tips.
Key Characters:
Flowers purplish pink in umbels that are taller than the leaves. No aerial stems. Leaflets with a fishtail shape.
Biology:
Life cycle:
Perennial or annual. Bulbs and bulbils shoot in autumn and produce a rosette of leaves. A carrot like taproot with fibrous feeder roots forms at the bases of the bulb and underground, stoloniferous stems form in the axils of the leaf bases. About 8 weeks after germination buds form at the ends of the stolons and bulbils start to develop. A new bulb starts to develop underneath the mother bulb at the same time. Flower stems are produced about 8 weeks later or 15-16 weeks after germination and reaches a peak 5-8 weeks later and continues to October or November. The new bulb starts to expand after flowering starts and continues growth until the top growth starts to die as temperatures increase. It then absorbs the reserves of the tap root which contracts and draws the bulb deeper into the ground. Bulbils produce leaves and form a new larger bulb annually for 1 or 2 years before flowering.
Physiology:
Bulbil formation by the parent plant depends on the amount of top growth produces. They do not receive reserves directly from the mother bulb. Defoliation or reduction in top growth before bulb exhaustion reduces bulbil production. Bulbils are normally fully formed by the time the new mother bulb starts growing.
Reproduction:
The plant reproduces by bulbs and bulbils produced from the underground stems.
Flowering times:
Spring.
Seed Biology and Germination:
No seed produced in Australia.
Vegetative Propagules:
Bulbs and bulbils.
Up to 50% of the bulbils are dormant at maturity and some may remain dormant for 2 years. Dormancy can be broken by chilling or dry heating followed by moist storage.
Some bulbils can establish from depths of 240 mm.
Up to 35 t/ha of bulbs and bulbils have been recorded in New Zealand.
Hybrids:
Three bio types with differing stamen and style lengths like Soursob. Seed is only produced when these bio types cross. In Australia there is only one bio type, so no seed is formed.
Allelopathy:
Population Dynamics and Dispersal:
Spread is entirely by the introduction of bulbs or bulbils, or soil containing them. Road and earth works are a major form of spread.
The size of colonies increases 100-200 mm per year by the growth of stolons. Local spread may also be assisted by insects moving bulbils.
Each plant produces about 50 bulbils per year.
Origin and History:
Mexico. South America.
Introduced as an ornamental in the 1800's.
Distribution:
NSW, QLD, SA, TAS, VIC.
In all parts of Tasmania.
In WA, species previously identified as Oxalis latifolia are Oxalis violacea.
Habitats:
Gardens.
Climate:
Temperate and sub tropical.
Soil:
Wide range.
More abundant on organic soils.
Plant Associations:
Significance:
Beneficial:
Ornamental.
Detrimental:
Weed of vegetables, carrots, sugar, irrigated crops, gardens, nature strips and reserves in the cities and towns, and in cemeteries. Occasionally a roadside weed outside urban areas. An invasive species in gardens. Regarded by many as the most serious weed of domestic gardens.
Toxicity:
Can cause oxalate poisoning in sheep.
Legislation:
Noxious weed of Tasmania.
Management and Control:
Difficult to control. Herbicides are the most effective form of control. Cultivation is generally ineffective and usually results in greater infestations. It can be partially effective at bulb exhaustion stage which often occurs near the time of first flowers. Plants need to be dug up to determine the stage as it varies from year to year. Mowing is also generally ineffective, but some reductions are reported if is repeated and conducted before the plant reaches the 20 leaf stage. Combinations of mowing, cultivation and replanting to vigorous pastures are used in some areas.
Fumigation with Metham sodium is effective but expensive.
Diuron, linuron, oxadiazon, oxyfluorfen, simazine, trifluralin, bromoxynil + MCPA, amitrole, glyphosate, terbacil and sulfonyl urea herbicides all provide control in various situations.
Control needs to be continued for at least 3 years to deplete dormant bulbil reserves.
Thresholds:
Eradication strategies:
Mowing and grazing are generally ineffective and manual removal very difficult.
Best control with herbicides usually occurs around the bulb exhaustion stage which is often just before flowering. Dig up plants and inspect the bulbs which should be shrivelled and the new bulb not formed. Bulbils on roots should be less than 1 mm round.
Sulfonyl urea herbicides and diuron usually provide the best control. For spot spraying, 0.1 g metsulfuron(600g/kg) or 0.2 g chlorsulfuron(750g/kg) plus 25 mL wetting agent in 10 L water applied when the plants are actively growing provides good control. Repeat this if regrowth appears. 100 mL glyphosate(450g/L) in 10 L of water when the plants are young and actively growing can be used where no residual action is desired.
50 mL diuron(500g/L) in 10 L of water will kill plants and leaves a soil residue to help control corms or seeds germinating after spraying. Diuron can damage many species of trees and native plants and should not be applied above the root zone of desirable plants or where water flows may take it to the root zone of desirable plants.
For broadacre spraying use 20 g/ha chlorsulfuron(750g/kg) plus 0.25% wetting agent. Logran and Spinnaker are also useful and generally cause less damage to native species where overall spraying is necessary.
It usually takes 3 or more years to achieve high levels of control.
300 mL/ha Spinnaker® controls O. purpurea in pasture and 50 g/ha Logran® controls O. glabra wheat. These products will probably also kill other Oxalis species.
Fumigation with metham sodium is useful for limited areas such as seed beds and glasshouses.
Herbicide resistance:
Biological Control:
Related plants:
Bowie's Wood Sorrel (Oxalis bowiei)
Chilean Wood Sorrel (Oxalis perdicaria)
Coastal Oxalis (Oxalis radicosa)
Finger-leaf Oxalis (Oxalis glabra) is a herb with an erect thin leafy stem and single large flowers held above the leaves. The leaflets are small and narrower than those of the other species. The flowers are pink to purple (or occasionally white) with a yellow throat. It is a weed of heavier soils in disturbed woodland and occurs from Perth to York, south to Augusta and around Kojonup.
Hairy Wood Sorrel (Oxalis hirta)
Large-flowered Wood Sorrel or Four O'clock (Oxalis purpurea) has a rosettes of leaves, that may be tinged purple on the underside, and arise from a bulb. The flowers occur singly and are usually pink to purple with a yellow throat but sometimes white with a yellow throat.
Native Oxalis (Oxalis perennans) a very similar native species that has larger yellow flowers, woody stems and a tuberous rootstock and is often confused with Yellow Wood Sorrel.
Pale-flowered Oxalis (Oxalis incarnata) is a delicate sprawling herb with clusters of green leaves at the ends of the stems and single white to pale pink flowers held above the leaves. It is often a weed of woodland or Karri forest.
Pink Bulb Soursob (Oxalis flava)
Pink Shamrock (Oxalis corymbosa or Oxalis debilis)
Shamrock Oxalis (Oxalis articulata)
Soursob (Oxalis pes-caprae) is a herb which grows from tubers and bulbs, with clusters of yellow flowers radiating from a tall stalk held above the tuft of long-stalked leaves. The leaflets sometimes have dark markings.
Yellow Wood Sorrel (Oxalis corniculata) is a creeping herb with much-branched and sometimes reddish stems that root at many points. It has single flowers or small clusters of yellow flowers occurring among the leaves.
Oxalis bifurca
Oxalis brasiliensis
Oxalis caprina
Oxalis compressa
Oxalis depressa
Oxalis lactea
Oxalis violacea is often incorrectly identified as Oxalis latifolia.
Oxalis tetraphylla
No native Oxalis species have bulbs.
Plants of similar appearance:
Clovers, Medics, Trefoils.
References:
Auld, B.A. and Medd R.W. (1992). Weeds. An illustrated botanical guide to the weeds of Australia. (Inkata Press, Melbourne). P194.
Hyde-Wyatt, B.H. and Morris, D.I. (1975). Tasmanian weed handbook. (Tasmanian Department of Agriculture, Hobart, Tasmania). P101.
Hyde-Wyatt, B.H. and Morris, D.I. (1980) The Noxious and Secondary Weeds of Tasmania. (Tasmanian Department of Agriculture, Hobart, Tasmania). P72-73. Diagram.
Lamp, C. and Collet, F. (1990). A Field Guide to Weeds in Australia. (Inkata Press, Melbourne). p194.
Lazarides, M. and Hince, B. (1993). CSIRO handbook of economic plants of Australia. (CSIRO, Melbourne). #919.12.
Parsons, W.T. and Cuthbertson, E.G. (1992). Noxious weeds of Australia. (Inkata Press, Melbourne). P526-529. Photos.
Acknowledgments:
Collated by HerbiGuide. Phone 08 98444064 or www.herbiguide.com.au for more information.