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.
These plants are annual or perennial. 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 clovers. Some species exhibit rapid changes in leaf angle in response to temporarily high light intensity to decrease photoinhibition.
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 xanthophylls 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, which detach to produce new plants.
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's Handbook of Edible Weeds, he notes that the native American Kiowa people chewed wood sorrel to alleviate thirst on long trips, the Potawatomi cooked it with sugar to make a dessert, the 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.
An apricot-coloured variety of Oxalis tuberosa for eating
The fleshy, juicy edible tubers of the 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.
In India, creeping wood sorrel (O. corniculata) is eaten only seasonally, starting in December-January. The 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.
Oxalis versicolor (candycane sorrel) grown in New Zealand
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. 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 sprouts, grapefruit, chives, and rhubarb, among many others. General scientific consensus seems to be that the risk of sheer toxicity, actual poisoning from oxalic acid in persons with normal kidney function is "wildly unlikely".[better source needed]
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.
Oxalis flowers range in colour from whites to yellows, peaches, pinks, 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 O. tetraphylla (four-leaved pink-sorrel) – are sometimes misleadingly sold as "four-leaf clover", taking advantage of the mystical status of four-leaf clover.
^S. L. Nielsen, A. M. Simonsen (September 2011). "Photosynthesis and photoinhibition in two differently coloured varieties of Oxalis triangularis -- the effect of anthocyanin content". Photosynthetica. 49 (3): 346-352. doi:10.1007/s11099-011-0042-y.
^http://oxalicacidinfo.com/ "Sheer toxicity - actual poisoning - from ingested oxalic acid is wildly unlikely. The only foodstuff that contains oxalic acid at concentrations high enough to be an actual toxicity risk is the leaves - not the stalks, which is what one normally eats - of the rhubarb plant. (And you'd need to eat an estimated 11 pounds (5kg) of rhubarb leaves at one sitting for a lethal dose, though you'd be pretty sick with rather less.)"
^http://dietary-supplements.info.nih.gov/factsheets/calcium.asp "Other components in food: phytic acid and oxalic acid, found naturally in some plants, bind to calcium and can inhibit its absorption. Foods with high levels of oxalic acid include spinach, collard greens, sweet potatoes, rhubarb, and beans. Among the foods high in phytic acid are fiber-containing whole-grain products and wheat bran, beans, seeds, nuts, and soy isolates. The extent to which these compounds affect calcium absorption varies. Research shows, for example, that eating spinach and milk at the same time reduces absorption of the calcium in milk. In contrast, wheat products (with the exception of wheat bran) do not appear to have a negative impact on calcium absorption. For people who eat a variety of foods, these interactions probably have little or no nutritional consequence and, furthermore, are accounted for in the overall calcium DRIs, which take absorption into account."
Bais, Harsh Pal; Vepachedu, Ramarao & Vivanco, Jorge M. (2003): Root specific elicitation and exudation of fluorescent ?-carbolines in transformed root cultures of Oxalis tuberosa. Plant Physiology and Biochemistry41(4): 345-353. doi:10.1016/S0981-9428(03)00029-9Preprint PDF fulltext