Oxalis

Oxalis(/ˈɒksəlɪs/(American English)or/ɒksˈɑːlɪs/(British English))is a largegenusofflowering plantsin the wood-sorrel family,Oxalidaceae, comprising over 550 species.The genus occurs throughout most of the world, except for thepolarareas; species diversity is particularly rich in tropicalBrazil,Mexico, andSouth Africa.
Many of the species are known aswood sorrels(sometimes written "woodsorrels" or "wood-sorrels") as they have an acidic taste reminiscent of the sorrel proper (Rumex acetosa), which is not closely related. Some species are calledyellow sorrelsorpink sorrelsafter the color of their flowers instead. Other species are colloquially known asfalseshamrocks, and some calledsourgrasses. For the genus as a whole, the termoxalisesis also used.
The plants areannualorperennial. 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, superficially similar to those of someclovers.Some species exhibit rapid changes in leaf angle in response to temporarily high light intensity to decreasephotoinhibition.
The flowers have five petals, which are usually fused at the base, and tenstamens. The petal color varies from white to pink, red or yellow;anthocyaninsandxanthophyllsmay 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 smallcapsulecontaining several seeds. The roots are often tuberous and succulent, and several species also  reproduce vegetatively by production ofbulbils, which detach to produce new plants.
SeveralOxalisspecies dominate the plant life in local woodland ecosystems, be itCoast Range ecoregionof theNorth AmericanPacific Northwest, or theSydney Turpentine-Ironbark Forestin 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) and sessile oak (Quercus petraea), by sycamore maple (Acer pseudoplatanus),common bracken(Pteridium aquilinum), pedunculate oak (Q. robur) andblackberries(Rubus fruticosusagg.), or by common ash (Fraxinus excelsior),dog's mercury(Mercurialis perennis) and European rowan (Sorbus aucuparia); it is also common in woods of common juniper (Juniperus communisssp.communis). Some species – notablyBermuda-buttercup(O. pes-caprae) andcreeping 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 studysuggested that species from thisgenushave a symbiotic relationship with nitrogen fixingBacillusendophytes, 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 smallherbivores– such as theMontezuma quail(Cyrtonyx montezumae). The foliage is eaten by someLepidoptera, such as thePolyommatinipale grass blue(Pseudozizeeria maha) – which feeds on creeping wood sorrel and others – anddark grass blue(Zizeeria lysimon).
Oxalisspecies are susceptible torust(Puccinia oxalidis).
Wood sorrel (a type of oxalis) is an edible wild plant that has been consumed by humans around the world for millennia.In Dr. James Duke'sHandbook of Edible Weeds,he notes that the Native AmericanKiowapeople chewed wood sorrel to alleviate thirst on long trips, thePotawatomicooked it with sugar to make a dessert, theAlgonquinconsidered it anaphrodisiac, the Cherokee ate wood sorrel to alleviate mouth sores and a sore throat, and theIroquoisate wood sorrel to help with cramps, fever and nausea.
The fleshy, juicy edibletubersof theoca(O. tuberosa) have long been cultivated for food inColombiaand elsewhere in the northernAndes mountainsofSouth America. It is grown and sold inNew Zealandas "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 bysailorstravelling aroundPatagoniaas a source ofvitamin Cto avoidscurvy.
InIndia, creeping wood sorrel (O. corniculata) is eaten only seasonally, starting in December–January. TheBodosof 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.
In the past, it was a practice to extract crystals ofcalcium oxalatefor use in treating diseases and as asaltcalledsal acetosellaor"sorrel salt"(also known as "salt of lemon"). Growing oca tuberroot capsare covered in afluorescentslush rich inharmalineandharminewhich apparently suppressespests.Creeping wood sorrel and perhaps other species are apparentlyhyperaccumulatorsofcopper. TheMing DynastytextPrecious Secrets of the Realm of the King of Xinfrom 1421 describes howO. corniculatacan be used to locate copper deposits as well as forgeobotanical prospecting. It thus ought to have some potential forphytoremediationof contaminated soils.
Several species are grown aspot plantsor asornamental plantsingardens, 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 ofO. compressus. Some varieties are grown for their foliage, such as the dark purple-leavedO. triangularis.
Species with four regular leaflets – in particularO. tetraphylla(four-leaved pink-sorrel) – are sometimes misleadingly sold as "four-leafclover", taking advantage of the mystical status offour-leaf clover.