Oxalis

From The Plant Encyclopedia

Jump to: navigation, search

Upload an image
Oxalis griffithii

Loading slideshow...

Oxalis

Category
Kingdom Plantae
Division
Class
Order Oxalidales
Family Oxalidaceae
Species in this genus
Add a species

Please enter the plant name in this format: 'Latin name - Common Name'

Aden Earth Zone

-

Cultivation

Characteristics

About

Oxalis ()<ref>Sunset Western Garden Book, 1995:606–607</ref> is by far the largest genus in the wood-sorrel family Oxalidaceae: of the approximately 900 known species in the Oxalidaceae, 800 belong here. The genus occurs throughout most of the world, except for the polar areas; species diversity is particularly rich in tropical Brazil, Mexico and South Africa.

Many of the species are known as wood-sorrels (in American English typically written "woodsorrels" or "wood sorrels") as they have an acidic taste reminiscent of the unrelated sorrel (Rumex acetosa) proper. 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 are rather misleadingly called "sourgrasses". For the genus as a whole, the term oxalises is also used.

Description and ecology

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.

File:Lyc oviposit.jpg
Pale Grass Blue (Pseudozizeeria maha) of the dry-season brood laying eggs on Oxalis

Several Oxalis species dominate the plant life in local woodland ecosystems, be it in the Coast Range ecoregion of the North American Pacific Northwest, or the Sydney Turpentine-Ironbark Forest 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) and sessile oak (Quercus petraea), by sycamore maple (Acer pseudoplatanus), common bracken (Pteridium aquilinum), pedunculate oak (Q. robur) and blackberries (Rubus fruticosus agg.), 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 communis 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.

Tuberous woodsorrels provide food for certain small herbivores – such as the Montezuma Quail (Cyrtonyx montezumae). The foliage is eaten by some Lepidoptera, such as the Polyommatini Pale Grass Blue (Pseudozizeeria maha) – which feeds on creeping wood sorrel and others – and Dark Grass Blue (Zizeeria lysimon).

Use by humans

Wood sorrel is an edible wild plant that has been consumed by humans around the world for millennia.<ref>http://books.google.com/books?id=rVrteo-8cI0C "Handbook of Edible Weeds" By Dr. James A. Duke, pp. 140-141</ref> In Dr. James Duke's "Handbook of Edible Weeds," he notes that the Kiowa Indian tribe chewed wood sorrel to alleviate thirst on long trips, that the Potawatomi Indians cooked it with sugar to make a dessert, the Algonquin Indians 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.<ref>http://books.google.com/books?id=rVrteo-8cI0C "Handbook of Edible Weeds" By Dr. James A. Duke, pp. 140-141</ref>

File:Oca.jpg
Some oca (O. tuberosa) tubers
The edible tubers of the oca (O. tuberosa), somewhat similar to a small potato, have long been cultivated for food in Colombia and elsewhere in the northern Andes mountains of South America. 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 only eaten seasonally, starting December/January. The leaves of common wood sorrel (O. acetosella) may be used to make a lemony-tasting tea when dried.
File:OxalicAcid-spaceFilling.png
Oxalic acid, the toxin found in many wood-sorrels and other edible plants

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.<ref>Łuczaj (2008)</ref> In very large amounts, oxalic acid may be considered slightly toxic, interfering with proper digestion and kidney function. It should be noted, however, that oxalic acid is also present in more commonly consumed foods such as spinach, broccoli, brussel sprouts, grapefruit, chives, and rhubarb, among many others.<ref>http://www.nal.usda.gov/fnic/foodcomp/Data/Other/oxalic.html "Oxalic Acid Content of Selected Vegetables"</ref> 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".<ref>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 eleven pounds of rhubarb leaves at one sitting for a lethal dose, though you'd be pretty sick with rather less.)"</ref> 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.<ref>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."</ref>

In the past, it was a practice to extract crystals of calcium oxalate for use in treating diseases and as a salt called sal acetosella or "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 pests; this phenomenon has been studied to some extent at the Colorado State University.<ref>Bais et al. (2002, 2003)</ref> 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.

Several species are grown as pot plants or as ornamental plants in gardens. 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 clovers.

Selected species

File:Oxalis arborea1.jpg
Oxalis articulata Savign. forma crassipes (Urb.) Lourteig, 1982
File:Oxalis articulata rubra0.jpg
Oxalis articulata Savign. subspecies rubra (A.St.-Hil.) Lourteig, 1982
File:Oxalis corymbosa 2.jpg
Oxalis debilis Kunth varietas corymbosa (DC.) Lourteig, 1981


See also

Footnotes

Unknown extension tag "references"

References

External links

Retrieved from "http://www.theplantencyclopedia.org/wiki/Oxalis"
Personal tools
Namespaces
Variants
Actions