Oxalis is from the Greek oksos meaning sour and refers to the taste of the leaves and stems.
Corniculata means horned and refers to the beaked or horned seed capsules.
Yellow Wood Sorrel
Other names:
Clover Sorrel
Creeping Oxalis
Creeping Wood Sorrel
Fish Tailed Oxalis
Small leaved Oxalis
Sourgrass
Sour weed
Summary:
A low growing, creeping, much branched, weak stemmed, stoloniferous annual plant with trifoliate leaves, heart shaped leaflets and a sour taste. It has single or small clusters of 5 petalled, yellow flowers with 10 stamens and 5 styles, nestled amongst the leaves at most times of the year with a flush in spring. These form an angular cylindrical seed capsule. It has no bulbs. The often reddish stems form roots at many points.
Native to South Africa it has become a weed in gardens, crops, pasture, and along roadsides.
Description:
Cotyledons:
Two.
Leaves:
Alternate. At the ends of stems or on the aerial part of the stem. Have 3 leaflets.
Stipules - Small, flat topped, usually thin. Hairs on the edges.
Petiole - 20-90 mm long. Slender. Winged at the base.
Blade - Of leaflet, wedge to heart shaped, deeply notched, 3-16 mm long by 7-17 mm wide, stalkless. Tip indented. Sides convex to straight and angular. Base tapered. Surface usually hairless on top or hairs restricted to nerves and edges, hairy underneath, often more hairy when young. Light sensitive. Often folded, especially at night or on dull days. Often tinged with red or red veins.
Stems:
Creeping and bending upwards, much branched, weak or wiry, 100-300 mm long. Softly to sparsely hairy. Stoloniferous. Often produce roots at nodes. Often tinged with red.
Flowering stems - Erect with fine silky hairs.
Flower head:
On stalks (peduncles), 50-125 mm long, that arise from the leaf axils with a 1-6 flowered umbel. Flower stems (pedicels) often bent back when in fruit and have 2 bracts at the base.
Flowers:
5 lobed, yellow, trumpet shape bisexual flowers.
Ovary - Superior, 5 celled, many pendulous ovules. 5 hairy, free styles with terminal stigmas.
Sepals - 5, overlapping, egg shaped, 3-6 mm long, obtuse tip. Hairy or hairless but usually hairy at the tip. No callus.
Petals - 5, yellow, overlapping, 6-15 mm long. 2-3 times as long as sepals.
Stamens - 10 in 2 rings. Outer ones shorter and opposite the petals. Filaments hairless and joined near the base.
Anthers - 5 or 10, release pollen by a longitudinal slit.
Fruit:
Thin walled capsule, 5-25 mm long, 4 angled and cylindrical with beaks to quadrangular and narrowed into persistent styles at the top. Dense backward bent hairs. Seeds expelled explosively through longitudinal slits leaving the valves attached to the plant. 5 cells with several seeds in each cell.
Seeds:
Reddish brown, flattened, crosswise wrinkles, outer fleshy covering which opens elastically. Many produced.
Roots:
Fibrous or occasionally with a weak slightly fleshy taproot. No bulb. Creeping stems form fibrous roots at the nodes.
Key Characters:
Trifoliate leaves. Yellow flowers. Stems with leaves and peduncles. Flowers single or 2-6 in umbels. Creeping stems rooting at the nodes. Fibrous roots and no bulbs.
Biology:
Life cycle:
Annual (or perennial). Flowers mainly in October to November with occasional flowers throughout the year that produce explosive pods to distribute seed. Maintains its foliage throughout the year.
Physiology:
Light sensitive leaves that fold up at night.
Reproduction:
By seed.
Flowering times:
Most of the year in western NSW.
Most of the year in SA.
October to November in Perth.
Spring and summer in WA.
Seed Biology and Germination:
Produces large quantities of seed.
Vegetative Propagules:
None.
Hybrids:
Several forms.
1) has 4-5 mm long hairy sepals with 9-12 mm long petals with hairs on the edges and seeds have crosswise pits in lengthwise lines.
2) has 2-3 mm long sepals that are almost hairless except at the apex, 6-7 mm long petals and seeds with that are crosswise rugose.
Allelopathy:
Population Dynamics and Dispersal:
Spread by seed. It is the only Oxalis that produces large amounts of seed and relies on it for dispersal.
Origin and History:
Europe, but almost cosmopolitan.
Distribution:
ACT, NSW, NT, QLD, SA, TAS, VIC, WA.
Habitats:
Climate:
Temperate. Mediterranean.
Soil:
On most soils. Often more abundant on poorly drained, acid soils.
Plant Associations:
Jam or Acacia communities especially around granite outcrops.
Many others also.
Significance:
Beneficial:
Fodder.
Ornamental.
Detrimental:
Weed of turf, pasture, woodlands, gardens and disturbed areas.
One of the few weeds that competes effectively with couch.
Toxicity:
May cause oxalate poisoning.
Most reports are from hungry sheep being exposed to dense stands. Pregnant ewes appear to be the most sensitive stock, followed by lambs then wethers then cattle.
Oxalate crystals may form in the kidneys causing permanent damage.
Animals accustomed to the plant usually don't have problems.
Symptoms:
Muscular trembling and or rigidity, staggering, heavy breathing, loss of control of the hindquarters, collapse onto the brisket with the head craned forward on the ground and to the side or lie on their side with legs out stretched, slimy discharge from the nostrils.
Death occurs from a few hours after consumption and up to 6 weeks later.
In chronic cases there is a loss of condition.
Treatment:
Calcium borogluconate 40% injected into the veins or under the skin. 60 mL for sheep and 300 mL for cattle. Must be applied as soon as possible before kidneys are damaged.
This may be supplemented with 250-1000 mL lime water or 2-5 g chalk in water or 60-100 g Epsom salts given by mouth for sheep.
Recovery may take weeks or not occur.
Legislation:
None.
Management and Control:
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.
Fishtail Oxalis (Oxalis latifolia) is a larger plant.
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.
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:
Clover.
References:
Auld, B.A. and Medd R.W. (1992). Weeds. An illustrated botanical guide to the weeds of Australia. (Inkata Press, Melbourne). P194-195. Photo.
Black, J.M. (1965). Flora of South Australia. (Government Printer, Adelaide, South Australia). P481, 484. Diagram.
Burbidge, N.T. and Gray, M. (1970). Flora of the Australian Capital Territory. (Australian National University Press, Canberra). P237, 239. Diagram.
Cunningham, G.M., Mulham, W.E., Milthorpe, P.L. and Leigh, J.H. (1992). Plants of Western New South Wales. (Inkata Press, Melbourne). 435. Photo.
Everist, S.L. (1974). Poisonous Plants of Australia. (Angus and Robertson, Sydney). P559-560.
Gardner, G.A. and Bennetts, H.W. (1956). The toxic plants of Western Australia. (West Australian Newspapers Ltd, Perth). P118.
Hussey, B.M.J., Keighery, G.J., Cousens, R.D., Dodd, J. and Lloyd, S.G. (1997). Western Weeds. A guide to the weeds of Western Australia. (Plant Protection Society of Western Australia, Perth, Western Australia). P190. Photo.
Hyde-Wyatt, B.H. and Morris, D.I. (1975). Tasmanian weed handbook. (Tasmanian Department of Agriculture, Hobart, Tasmania). P100-101. Diagram.
Lamp, C. and Collet, F. (1990). A Field Guide to Weeds in Australia. (Inkata Press, Melbourne).
Lazarides, M. and Hince, B. (1993). CSIRO handbook of economic plants of Australia. (CSIRO, Melbourne). #919.5.
Marchant, N.G., Wheeler, J.R., Rye, B.L., Bennett, E.M., Lander, N.S. and Macfarlane, T.D. (1987). Flora of the Perth Region. (Western Australian Herbarium, Department of Agriculture, Western Australia). P493-494. Diagram.