Oxalis pes-caprae
Encyclopedia
Oxalis pes-caprae is a species of tristylous
flowering plant in the wood sorrel family Oxalidaceae
. Oxalis cernua is a less common synonym for this species.
s, a sympetalous
corolla composed of five fused petals, an apoandrous androecium composed of ten free stamen
s in two ranks, and a compound pistil
. Like most African Oxalis species, it produces adventitious subterranean propagules. These take the form of true bulbs in botanical terms, which is unusual among dicotyledon
s. In fact, Oxalis pes-caprae produces small bulbs copiously, whereas most other African species produce fewer, larger bulbs. New world Oxalis, such as Oxalis corniculata, apparently do not generally produce bulbs.
and noxious weed in many other parts of the world, including the United States
(particularly coastal California
), Europe
, Israel
and Australia
.
Kluge & Claassens (1990) reported a potential biocontrol agent using Klugeana
philoxalis, a larval feeder on shoots of O. pes-caprae.
O. pes-caprae is also a host to broomrape
, though it is not clear that that is of significance as a control agent.
or soursob due to its pleasant sour flavor. This sourness is caused by the exceptionally high content of oxalic acid
.
The plant is palatable and in modest quantities is reasonably harmless to humans and livestock. In South Africa it is a traditional ingredient in dishes such as waterblommetjiebredie
(water flower stew).
The plant has been used in various ways as a source of oxalic acid, as food, and in folk medicine. The raw bulbs have been used to deal with tapeworm and possibly other worms. The plant has been used as a diuretic, possibly hazardously, in the light of observations in the following section. The lateral underground runners, which tend to be fleshy, have been eaten raw or boiled and served with milk.
make it unlikely that any realistic intake of Oxalis would affect human liability to kidney stones. Accordingly, some Australian references to the hazards of oxalis to livestock tend to be dismissive.
However, in spite of its comparatively benign nature, where it has become dominant in pastures, as sometimes happens outside South Africa, Oxalis pes-caprae certainly can cause dramatic stock losses. For example, when hungry stock, such as sheep released just after being shorn, are let out to graze in a lush growth of Oxalis pes-caprae, they may gorge on the plant, with fatal results, as has been found in South Australia at least.
Such stock fatalities patently have little logical connection with the presence or absence of oxalate kidney stones. For one thing, the fatal effects on sheep are far too rapid to result from the growth of bulk kidney stones. The plant has been found to be nutritious, but too acid to be good fodder, largely being left untouched by grazing stock. When stock do consume large quantities, the effects typically involve death in several weeks with symptoms suggesting chronic oxalate poisoning, including tetany or sudden death with extensive renal damage. Such damage suggests the twofold effect of calcium immobilisation (the tetany) and the formation of Calcium Oxalate Monohydrate raphides in the kidney tissue. The histotoxic effects of the raphides in kidney have by now been investigated.
Oxalis poisoning of stock is not a serious forage
concern in South African pastures, unless exceptionally favoured by overgrazing
.
Heterostyly
Heterostyly is a unique form of polymorphism and herkogamy in flowers. In a heterostylous species, two or three different morphological types of flowers, termed morphs, exist in the population. On each individual plant, all flowers share the same morph. The flower morphs differ in the lengths of...
flowering plant in the wood sorrel family Oxalidaceae
Oxalidaceae
The Oxalidaceae, or wood sorrel family, are a small family of eight genera of herbaceous plants, shrubs and small trees, with the great majority of the 900 species in the genus Oxalis...
. Oxalis cernua is a less common synonym for this species.
Description
The Oxalis pes-caprae flower is actinomorphic, with a calyx composed of five free or slightly fused sepalSepal
A sepal is a part of the flower of angiosperms . Collectively the sepals form the calyx, which is the outermost whorl of parts that form a flower. Usually green, sepals have the typical function of protecting the petals when the flower is in bud...
s, a sympetalous
Sympetaly
' is the condition of some flowers in which the petals are fused together . in some of these flowers, like with Gentiana asclepiadea are only partially fused at the base, but in other flowers, such as Gentiana andrewsii, they are fully fused and never open...
corolla composed of five fused petals, an apoandrous androecium composed of ten free stamen
Stamen
The stamen is the pollen producing reproductive organ of a flower...
s in two ranks, and a compound pistil
Gynoecium
Gynoecium is most commonly used as a collective term for all carpels in a flower. A carpel is the ovule and seed producing reproductive organ in flowering plants. Carpels are derived from ovule-bearing leaves which evolved to form a closed structure containing the ovules...
. Like most African Oxalis species, it produces adventitious subterranean propagules. These take the form of true bulbs in botanical terms, which is unusual among dicotyledon
Dicotyledon
The dicotyledons, also known as dicots, are a group of flowering plants whose seed typically has two embryonic leaves or cotyledons. There are around 199,350 species within this group...
s. In fact, Oxalis pes-caprae produces small bulbs copiously, whereas most other African species produce fewer, larger bulbs. New world Oxalis, such as Oxalis corniculata, apparently do not generally produce bulbs.
Invasive species
Indigenous to South Africa, Oxalis pes-caprae, the "Bermuda buttercup", is a highly invasive speciesInvasive species
"Invasive species", or invasive exotics, is a nomenclature term and categorization phrase used for flora and fauna, and for specific restoration-preservation processes in native habitats, with several definitions....
and noxious weed in many other parts of the world, including the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
(particularly coastal California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
), Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
, Israel
Israel
The State of Israel is a parliamentary republic located in the Middle East, along the eastern shore of the Mediterranean Sea...
and Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
.
Control
The plant has a reputation for being very difficult to eliminate once it has spread over an area of land. The weed propagates largely through its underground bulbs and this is one reason why it is so difficult to eradicate, as pulling up the stems leaves the bulbs behind. Soil in which the plant has grown is generally filled with small bulbs. Another reason is that the seeds are tiny, hard, and sticky when ejected from the follicle. If they stick to an animal or vehicle, they may be carried far without detection (Africa).Kluge & Claassens (1990) reported a potential biocontrol agent using Klugeana
Klugeana
Klugeana is a genus of moths of the Noctuidae family.The South African species Klugeana philoxalis has been proposed as being of interest as a possible biocontrol agent for dealing with invasive Oxalis pes-caprae in countries where it is a problem. Like many Noctuids, Klugeana philoxalis has...
philoxalis, a larval feeder on shoots of O. pes-caprae.
O. pes-caprae is also a host to broomrape
Broomrape
Broomrape or Broom-rape is a genus of over 200 species of parasitic herbaceous plants in the family Orobanchaceae, mostly native to the temperate Northern Hemisphere. Some species formerly included in this genus are now referred to the genus Conopholis.The broomrape plant is small, from...
, though it is not clear that that is of significance as a control agent.
Uses
Oxalis pes-caprae is often called by the common name sourgrassSourgrass
Sourgrass is a common name given to several plant species which have a sour taste. Most are in fact not grasses:* Digitaria insularis, a true grass * Oxalis species of the Oxalidaceae, namely:...
or soursob due to its pleasant sour flavor. This sourness is caused by the exceptionally high content of oxalic acid
Oxalic acid
Oxalic acid is an organic compound with the formula H2C2O4. This colourless solid is a dicarboxylic acid. In terms of acid strength, it is about 3,000 times stronger than acetic acid. Oxalic acid is a reducing agent and its conjugate base, known as oxalate , is a chelating agent for metal cations...
.
The plant is palatable and in modest quantities is reasonably harmless to humans and livestock. In South Africa it is a traditional ingredient in dishes such as waterblommetjiebredie
Waterblommetjiebredie
Waterblommetjiebredie is a stew. The name comes from the Afrikaans language and literally means 'small water flower stew'. It is made of meat, typically lamb, stewed together with the waterblommetjies which are found in the dams and marshes of the Western Cape of South Africa...
(water flower stew).
The plant has been used in various ways as a source of oxalic acid, as food, and in folk medicine. The raw bulbs have been used to deal with tapeworm and possibly other worms. The plant has been used as a diuretic, possibly hazardously, in the light of observations in the following section. The lateral underground runners, which tend to be fleshy, have been eaten raw or boiled and served with milk.
Hazards
Oxalic acid is toxic in large quantities, a concern in regions such as southern Australia where Oxalis pes-caprae grows invasively in enormous quantities and in high densities. Various sources suggest that oxalis injestion causes calcium oxalate kidney stones, but clinical experience and physiological considerations as described in the Wikipedia article on kidney stoneKidney stone
A kidney stone, also known as a renal calculus is a solid concretion or crystal aggregation formed in the kidneys from dietary minerals in the urine...
make it unlikely that any realistic intake of Oxalis would affect human liability to kidney stones. Accordingly, some Australian references to the hazards of oxalis to livestock tend to be dismissive.
However, in spite of its comparatively benign nature, where it has become dominant in pastures, as sometimes happens outside South Africa, Oxalis pes-caprae certainly can cause dramatic stock losses. For example, when hungry stock, such as sheep released just after being shorn, are let out to graze in a lush growth of Oxalis pes-caprae, they may gorge on the plant, with fatal results, as has been found in South Australia at least.
Such stock fatalities patently have little logical connection with the presence or absence of oxalate kidney stones. For one thing, the fatal effects on sheep are far too rapid to result from the growth of bulk kidney stones. The plant has been found to be nutritious, but too acid to be good fodder, largely being left untouched by grazing stock. When stock do consume large quantities, the effects typically involve death in several weeks with symptoms suggesting chronic oxalate poisoning, including tetany or sudden death with extensive renal damage. Such damage suggests the twofold effect of calcium immobilisation (the tetany) and the formation of Calcium Oxalate Monohydrate raphides in the kidney tissue. The histotoxic effects of the raphides in kidney have by now been investigated.
Oxalis poisoning of stock is not a serious forage
Forage
Forage is plant material eaten by grazing livestock.Historically the term forage has meant only plants eaten by the animals directly as pasture, crop residue, or immature cereal crops, but it is also used more loosely to include similar plants cut for fodder and carried to the animals, especially...
concern in South African pastures, unless exceptionally favoured by overgrazing
Overgrazing
Overgrazing occurs when plants are exposed to intensive grazing for extended periods of time, or without sufficient recovery periods. It can be caused by either livestock in poorly managed agricultural applications, or by overpopulations of native or non-native wild animals.Overgrazing reduces the...
.
External links
- Jepson Manual Treatment: Oxalis pes-caprae
- USDA Plants Profile
- Oxalis pes-caprae - Photo gallery
- Photo gallery of Oxalis pes-caprae by Zachi Evenor, FlickrFlickrFlickr is an image hosting and video hosting website, web services suite, and online community that was created by Ludicorp in 2004 and acquired by Yahoo! in 2005. In addition to being a popular website for users to share and embed personal photographs, the service is widely used by bloggers to...