''Oxalis'' ( (American English) or (British English)) is a large

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

flowering plant Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek words ('container, vessel') and ('seed'), and refers to those plants th ...

s in the wood-sorrel family

Oxalidaceae The Oxalidaceae, or wood sorrel family, are a small family of five genera of herbaceous plants, shrubs and small trees, with the great majority of the 570 species in the genus ''Oxalis'' (wood sorrels). Members of this family typically have divid ...

, comprising over 550 species. The genus occurs throughout most of the world, except for the polar areas; species diversity is particularly rich in tropical

Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...

Mexico Mexico (Spanish: México), officially the United Mexican States, is a country in the southern portion of North America. It is bordered to the north by the United States; to the south and west by the Pacific Ocean; to the southeast by Guatema ...

, and

South Africa South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. It is bounded to the south by of coastline that stretch along the Atlantic Ocean, South Atlantic and Indian Oceans; to the ...

. Many of the species are known as wood sorrels (sometimes written "woodsorrels" or "wood-sorrels") as they have an acidic taste reminiscent of the sorrel proper ('' Rumex acetosa''), which is only distantly related. Some species are called yellow sorrels or pink sorrels after the color of their flowers instead. Other species are colloquially known as false shamrocks, and some called sourgrasses. For the genus as a whole, the term oxalises is also used.

Description and ecology

These plants are

annual Annual may refer to: *Annual publication, periodical publications appearing regularly once per year ** Yearbook ** Literary annual *Annual plant *Annual report *Annual giving *Annual, Morocco, a settlement in northeastern Morocco *Annuals (band), ...

perennial A perennial plant or simply perennial is a plant that lives more than two years. The term ('' per-'' + '' -ennial'', "through the years") is often used to differentiate a plant from shorter-lived annuals and biennials. The term is also wid ...

. The leaves are divided into three to ten or more obovate and top-notched leaflets, arranged palmately with all the leaflets of roughly equal size. The majority of species have three leaflets; in these species, the leaves are superficially similar to those of some

clover Clover or trefoil are common names for plants of the genus ''Trifolium'' (from Latin ''tres'' 'three' + ''folium'' 'leaf'), consisting of about 300 species of flowering plants in the legume or pea family Fabaceae originating in Europe. The genus ...

s. Some species exhibit rapid changes in leaf angle in response to temporarily high light intensity to decrease

photoinhibition Photoinhibition is light-induced reduction in the photosynthetic capacity of a plant, alga, or cyanobacterium. Photosystem II (PSII) is more sensitive to light than the rest of the photosynthetic machinery, and most researchers define the term ...

. The flowers have five petals, which are usually fused at the base, and ten stamens. The petal color varies from white to pink, red or yellow; anthocyanins and

xanthophyll Xanthophylls (originally phylloxanthins) are yellow pigments that occur widely in nature and form one of two major divisions of the carotenoid group; the other division is formed by the carotenes. The name is from Greek (, "yellow") and (, "lea ...

s may be present or absent but are generally not both present together in significant quantities, meaning that few wood-sorrels have bright orange flowers. The fruit is a small capsule containing several seeds. The roots are often tuberous and succulent, and several species also reproduce vegetatively by production of

bulbils A bulbil (also referred to as bulbel, bulblet, and/or pup) is a small, young plant that is reproduced vegetatively from axillary buds on the parent plant's stem or in place of a flower on an inflorescence. These young plants are clones of the p ...

, which detach to produce new plants. Lyc oviposit

Several ''Oxalis'' species dominate the plant life in local woodland ecosystems, be it Coast Range ecoregion of the North American

Pacific Northwest The Pacific Northwest (sometimes Cascadia, or simply abbreviated as PNW) is a geographic region in western North America bounded by its coastal waters of the Pacific Ocean to the west and, loosely, by the Rocky Mountains to the east. Tho ...

, or the

Sydney Turpentine-Ironbark Forest The Sydney Turpentine-Ironbark Forest (STIF) is dry sclerophyll forest community of Sydney, New South Wales, Australia, that is typically found in the Inner West and Northern region of Sydney. It is also among the three of these plant communities ...

in southeastern Australia where least yellow sorrel ('' O. exilis'') is common. In the United Kingdom and neighboring Europe, common wood sorrel ('' O. acetosella'') is the typical woodland member of this genus, forming large swaths in the typical mixed deciduous forests dominated by downy birch (''

Betula pubescens ''Betula pubescens'' (syn. ''Betula alba''), commonly known as downy birch and also as moor birch, white birch, European white birch or hairy birch, is a species of deciduous tree, native and abundant throughout northern Europe and northern Asia ...

'') and sessile oak (''

Quercus petraea ''Quercus petraea'', commonly known as the sessile oak, Cornish oak, Irish Oak or durmast oak, is a species of oak tree native to most of Europe and into Anatolia and Iran. The sessile oak is the national tree of Ireland, and an unofficial embl ...

''), by sycamore maple ('' Acer pseudoplatanus''), common bracken (''Pteridium aquilinum''), pedunculate oak ('' Q. robur'') and

blackberries The blackberry is an edible fruit produced by many species in the genus ''Rubus'' in the family (biology), family Rosaceae, hybrids among these species within the subgenus ''Rubus'', and hybrids between the subgenera ''Rubus'' and ''Idaeobatus' ...

(''Rubus fruticosus'' agg.), or by common ash (''

Fraxinus excelsior ''Fraxinus excelsior'', known as the ash, or European ash or common ash to distinguish it from other types of ash, is a flowering plant species in the olive family Oleaceae. It is native throughout mainland Europe east to the Caucasus and Albor ...

''),

dog's mercury ''Mercurialis perennis'', commonly known as dog's mercury, is a poisonous woodland plant found in much of Europe as well as in Algeria, Iran, Turkey, and the Caucasus, but almost absent from Ireland, Orkney and Shetland.Sorbus aucuparia''); it is also common in woods of common juniper (''

Juniperus communis ''Juniperus communis'', the common juniper, is a species of small tree or shrub in the cypress family Cupressaceae. An evergreen conifer, it has the largest geographical range of any woody plant, with a circumpolar distribution throughout the coo ...

'' ssp. ''communis''). Some species – notably Bermuda-buttercup (''O. pes-caprae'') and creeping woodsorrel (''O. corniculata'') – are pernicious, invasive weeds when escaping from cultivation outside their native ranges; the ability of most wood-sorrels to store reserve energy in their tubers makes them quite resistant to most weed control techniques. A 2019 study suggested that species from this

have a symbiotic relationship with nitrogen fixing ''Bacillus'' endophytes, storing them in plant tissues and seeds, which could explain its ability to spread rapidly even in poor soils. Tuberous woodsorrels provide food for certain small herbivores – such as the

Montezuma quail The Montezuma quail (''Cyrtonyx montezumae'') is a stubby, secretive New World quail of Mexico and some nearby parts of the United States. It is also known as Mearns's quail, the harlequin quail (for the male's striking pattern), and the fool q ...

(''Cyrtonyx montezumae''). The foliage is eaten by some Lepidoptera, such as the

Polyommatini Polyommatini is a tribe of lycaenid butterflies in the subfamily of Polyommatinae. These were extensively studied by Russian novelist and lepidopterist Vladimir Nabokov. Genera Genera in this tribe include: * ''Actizera'' * '' Acytolepis'' * '' ...

pale grass blue (''Pseudozizeeria maha'') – which feeds on creeping wood sorrel and others – and dark grass blue (''Zizeeria lysimon''). ''Oxalis'' species are susceptible to

rust Rust is an iron oxide, a usually reddish-brown oxide formed by the reaction of iron and oxygen in the catalytic presence of water or air moisture. Rust consists of hydrous iron(III) oxides (Fe2O3·nH2O) and iron(III) oxide-hydroxide (FeO( ...

('' Puccinia oxalidis'').

Use by humans

As food

Wood sorrel (a type of oxalis) is an edible wild plant that has been consumed by humans around the world for millennia.https://books.google.com/books?id=rVrteo-8cI0C ''Handbook of Edible Weeds'' By Dr. James A. Duke, pp. 140-141 In Dr. James Duke's ''Handbook of Edible Weeds,'' he notes that the Native American

Kiowa Kiowa () people are a Native American tribe and an indigenous people of the Great Plains of the United States. They migrated southward from western Montana into the Rocky Mountains in Colorado in the 17th and 18th centuries,Pritzker 326 and e ...

people chewed wood sorrel to alleviate thirst on long trips, the Potawatomi cooked it with sugar to make a dessert, the Algonquin people, Algonquin considered it an aphrodisiac, the Cherokee ate wood sorrel to alleviate mouth sores and a sore throat, and the Iroquois ate wood sorrel to help with cramps, fever and nausea.

The fleshy, juicy edible tubers of the Oxalis tuberosa, oca (''O. tuberosa'') have long been cultivated for food in Colombia and elsewhere in the northern Andes mountains of South America. It is grown and sold in New Zealand as "New Zealand yam" (although not a true yam), and varieties are now available in yellow, orange, apricot, and pink, as well as the traditional red-orange. The leaves of scurvy-grass sorrel (''O. enneaphylla'') were eaten by sailors travelling around Patagonia as a source of vitamin C to avoid scurvy. In India, creeping wood sorrel (''O. corniculata'') is eaten only seasonally, starting in December–January. The Bodo people, Bodos of north east India sometimes prepare a sour fish curry with its leaves. The leaves of common wood sorrel ('' O. acetosella'') may be used to make a lemony-tasting tea when dried.

For its oxalic acid content

A characteristic of members of this genus is that they contain oxalic acid (whose name references the genus), giving the leaves and flowers a sour taste which can make them refreshing to chew. The crude calcium oxalate ranges from 13 to 25 mg/g fresh weight for woodsorrel as compared to 1.3 to 1.8 mg/g for spinach. In very large amounts, oxalic acid may be considered slightly toxic, interfering with proper digestion and kidney function. However, oxalic acid is also present in more commonly consumed foods such as spinach, broccoli, Brussels sprout, brussels sprouts, grapefruit, chives, and rhubarb, among many others. A non-medical expert summary is that, on the one hand, the risk of sheer toxicity, actual poisoning from oxalic acid in persons with normal kidney function is "wildly unlikely", while, in the other hand, the mechanical effects of crystals of calcium oxalate contribute substantially to some pathological conditions, such as gout and (especially) nephrolithiasis. While any oxalic acid-containing plant, such as ''Oxalis'', is toxic to humans in some dosage, the U.S. National Institutes of Health note that oxalic acid is present in many foodstuffs found in the supermarket and its toxicity is generally of little or no consequence for people who eat a variety of foods. In the past, it was a practice to extract crystals of calcium oxalate for use in treating diseases and as a Salt (chemistry), salt called ''sal acetosella'' or Potassium hydrogenoxalate, "sorrel salt" (also known as "salt of lemon"). Growing oca tuber root caps are covered in a fluorescent slush rich in harmaline and harmine which apparently suppresses Pest (organism), pests. Creeping wood sorrel and perhaps other species are apparently hyperaccumulators of copper. The Ming Dynasty text ''Precious Secrets of the Realm of the King of Xin'' from 1421 describes how ''O. corniculata'' can be used to locate copper deposits as well as for geobotanical prospecting. It thus ought to have some potential for phytoremediation of contaminated soils.

As ornamental plants

Several species are grown as pot plants or as ornamental plants in gardens, for example, ''O. versicolor''. Oxalis flowers range in colour from whites to yellow, peaches, pink, or multi-coloured flowers. Some varieties have double flowers, for example the double form of ''O. compressus''. Some varieties are grown for their foliage, such as the dark purple-leaved ''O. triangularis''. Species with four regular leaflets – in particular ''Oxalis tetraphylla, O. tetraphylla'' (four-leaved pink-sorrel) – are sometimes misleadingly sold as "four-leaf

", taking advantage of the mystical status of four-leaf clover.

Selected species

* ''Oxalis acetosella'' – common wood sorrel, stabwort * ''Oxalis adenophylla'' – Chilean oxalis, silver shamrock * ''Oxalis albicans'' – hairy woodsorrel, white oxalis, radishroot woodsorrel, radishroot yellow-sorrel, California yellow-sorrel * ''Oxalis alpina'' – alpine sorrel * ''Oxalis ambigua'' * ''Oxalis articulata'' Savign. – pink-sorrel * ''Oxalis ausensis'' * ''Oxalis barrelieri'' – lavender sorrel * ''Oxalis bowiei'' – Bowie's wood-sorrel, Cape shamrock * ''Oxalis brasiliensis'' – Brazilian woodsorrel * ''Oxalis caerulea'' – blue woodsorrel * ''Oxalis caprina'' * ''Oxalis corniculata'' – creeping wood sorrel, procumbent yellow-sorrel, sleeping beauty, ''chichoda bhaji'' (India) * ''Oxalis debilis'' Kunth * ''Oxalis decaphylla'' – ten-leaved pink-sorrel, tenleaf wood sorrel * ''Oxalis dehradunensis'' * ''Oxalis depressa'' * ''Oxalis dichondrifolia'' – peonyleaf wood sorrel * ''Oxalis dillenii'' Jacquin – southern yellow woodsorrel, Dillen's woodsorrel, Sussex yellow-sorrel * ''Oxalis drummondii'' – Drummond's woodsorrel, chevron oxalis * ''Oxalis ecuadorensis'' * ''Oxalis enneaphylla'' – scurvy-grass sorrel * ''Oxalis exilis'' – least yellow-sorrel * ''Oxalis frutescens'' – shrubby wood-sorrel * ''Oxalis gigantea'' * ''Oxalis glabra'' – finger-leaf * ''Oxalis grandis'' – great yellow-sorrel, large yellow woodsorrel * ''Oxalis griffithii'' Edgew. & Hook.f. * ''Oxalis hedysaroides'' – fire fern * ''Oxalis hirta'' – hairy sorrel * ''Oxalis illinoensis'' – Illinois wood-sorrel * ''Oxalis inaequalis'' * ''Oxalis incarnata'' L. – pale pink-sorrel * ''Oxalis lasiandra'' – Mexican shamrock * ''Oxalis latifolia'' Kunth – garden pink-sorrel * ''Oxalis luederitzii'' * ''Oxalis luteola'' Jacq. * ''Oxalis magellanica'' G.Forst. * ''Oxalis magnifica'' Kunth – snowdrop wood-sorrel * ''Oxalis massoniana'' * ''Oxalis megalorrhiza'' – fleshy yellow-sorrel * ''Oxalis melanosticta'' * ''Oxalis micrantha'' – dwarf woodsorrel * ''Oxalis montana'' – mountain woodsorrel, white woodsorrel * ''Oxalis nelsonii'' – Nelson's sorrel * ''Oxalis norlindiana'' * ''Oxalis obliquifolia'' * ''Oxalis oregana'' – redwood sorrel, Oregon sorrel * ''Oxalis ortgiesii'' Regel – fishtail oxalis * ''Oxalis pennelliana'' * ''Oxalis pes-caprae'' – Bermuda-buttercup, African wood-sorrel, Bermuda sorrel, buttercup oxalis, Cape sorrel, English weed, soursob, "goat's-foot", " sourgrass", soursop (not to be confused with soursop, the fruit of that name) * ''Oxalis priceae'' – tufted yellow-sorrel * ''Oxalis pulchella'' * ''Oxalis purpurea'' L. – purple wood-sorrel * ''Oxalis rosea'' Feuillée ex Jacq. – annual pink-sorrel * ''Oxalis rubra'' A.St.-Hil. – red wood-sorrel * ''Oxalis rufescens'' * ''Oxalis rugeliana'' – coamo * ''Oxalis schaeferi'' * ''Oxalis spiralis'' – spiral sorrel, volcanic sorrel, velvet oxalis * ''Oxalis stricta'' – common yellow woodsorrel, common yellow oxalis, upright yellow-sorrel, lemon clover, "pickle plant", " sourgrass, "yellow woodsorrel" * ''Oxalis suksdorfii'' – western yellow woodsorrel, western yellow oxalis * ''Oxalis tenuifolia'' – thinleaf sorrel * ''Oxalis tetraphylla'' – four-leaved pink-sorrel, four-leaf sorrel, Iron Cross oxalis, "lucky clover" * ''Oxalis triangularis'' – threeleaf purple shamrock * ''Oxalis trilliifolia'' – great oxalis, threeleaf woodsorrel * ''Oxalis tuberosa'' – oca, oka, New Zealand yam * ''Oxalis valdiviensis'' – Chilean yellow-sorrel * ''Oxalis virginea'' – virgin wood-sorrel * ''Oxalis versicolor'' – candycane sorrel * ''Oxalis violacea'' – violet wood-sorrel * ''Oxalis vulcanicola'' – volcanic sorrel or velvet oxalis