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Genus of flowering plants in the spurge family Euphorbiaceae

Euphorbia is a very large and diverse genus of flowering plants, commonly called spurge, in the family Euphorbiaceae. "Euphorbia" is sometimes used in ordinary English to collectively refer to all members of Euphorbiaceae (in deference to the type genus), not just to members of the genus. Euphorbias range from tiny annual plants to large and long lived trees. with perhaps the tallest being Euphorbia ampliphylla at or more. The genus has roughly 2,000 members, making it one of the largest genera of flowering plants. It also has one of the largest ranges of chromosome counts, along with Rumex and Senecio. It was first described by Carl Linnaeus in 1753 in Species Plantarum. Some euphorbias are widely available commercially, such as poinsettias at Christmas. Some are commonly cultivated as ornamentals, or collected and highly valued for the aesthetic appearance of their unique floral structures, such as the crown of thorns plant (Euphorbia milii). Succulent euphorbias from the deserts of Southern Africa and Madagascar have evolved physical characteristics and forms similar to cacti of North and South America, so they are often incorrectly referred to as cacti. Some are used as ornamentals in landscaping, because of beautiful or striking overall forms, and drought and heat tolerance. Juba was a prolific writer on various subjects, including natural history. Euphorbos wrote that one of the cactus like euphorbias (now called Euphorbia obtusifolia ssp. regis jubae) was used as a powerful laxative.

The plants are annual, biennial or perennial herbs, woody shrubs, or trees with a caustic, poisonous milky latex. The roots are fine or thick and fleshy or tuberous. Many species are more or less succulent, thorny, or unarmed. The main stem and mostly also the side arms of the succulent species are thick and fleshy, and often winged, tall. The succulent trees and large shrubs are mostly confined to southern and eastern Africa, but Euphorbia neutra is native to the Caatinga of Brazil and Euphorbia royleana is found in the Himalayan foothills. The deciduous leaves may be opposite, alternate, or in whorls. In succulent species, the leaves are mostly small and short lived. The stipules are mostly small, partly transformed into spines or glands, or missing.

Like all members of the family Euphorbiaceae, spurges have unisexual flowers. In Euphorbia, flowers occur in a head, called the cyathium (plural cyathia). Each male or female flower in the cyathium head has only its essential sexual part, in males the stamen, and in females the pistil. The flowers do not have sepals, petals, or nectar to attract pollinators, although other nonflower parts of the plant have an appearance and nectar glands with similar roles. Euphorbias are the only plants known to have this kind of flower head. Nectar glands and nectar that attract pollinators are held in the involucre, a cup like part below and supporting the cyathium head. The "involucre" in the genus Euphorbia is not to be confused with the "involucre" in family Asteraceae members, which is a collection of bracts called phyllaries, which surround and encase the unopened flower head, then support the receptacle under it after the flower head opens. The involucre is above and supported by bract like modified leaf structures (usually in pairs) called cyathophylls', or cyathial leaves. The cyathophyll often has a superficial appearance of being petals of a flower. Euphorbia flowers are tiny, and the variation attracting different pollinators, with different forms and colors occurs, in the cyathium, involucre, cyathophyll, or additional parts such as glands that attached to these. The collection of many flowers may be shaped and arranged to appear collectively as a single individual flower, sometimes called a pseudanthium in the Asteraceae, and also in Euphorbia. The majority of species are monoecious (bearing male and female flowers on the same plant), although some are dioecious with male and female flowers occurring on different plants. It is not unusual for the central cyathia of a cyme to be purely male, and for lateral cyathia to carry both sexes. Sometimes, young plants or those growing under unfavorable conditions are male only, and only produce female flowers in the cyathia with maturity or as growing conditions improve. The female flowers reduced to a single pistil usually split into three parts, often with two stigmas at each tip. Male flowers often have anthers in twos. Nectar glands usually occur in fives, may be as few as one, In contact with mucous membranes (eyes, nose, mouth), the latex can produce extremely painful inflammation. The sap has also been known to cause mild to extreme Keratouveitis, which affects vision. Latex on skin should be washed off immediately and thoroughly. Congealed latex is insoluble in water, but can be removed with an emulsifier such as milk or soap. A physician should be consulted if inflammation occurs, as severe eye damage including permanent blindness may result from exposure to the sap. The poisonous qualities were well known: in the Ethiopian Kebra Nagast, the serpent king Arwe is killed with juice from the Euphorbia.

Several spurges are grown as garden plants, among them poinsettia (E. pulcherrima) and the succulent E. trigona. E. pekinensis is used in traditional Chinese medicine, where it is regarded as one of the 50 fundamental herbs. Several Euphorbia species are used as food plants by the larvae of some Lepidoptera (butterflies and moths), like the spurge hawkmoths (Hyles euphorbiae and Hyles tithymali), as well as the giant leopard moth. Ingenol mebutate, a drug used to treat actinic keratosis, is a diterpenoid found in Euphorbia peplus. Euphorbias are often used as hedging plants in many parts of Africa.

Among laypeople, Euphorbia species are among the plant taxa most commonly confused with cacti, especially the stem succulents. Euphorbias secrete a sticky, milky white fluid with latex, but cacti do not. most of the smaller "satellite genera" around the huge genus Euphorbia nest deep within the latter. Consequently, these taxa, namely the never generally accepted genus Chamaesyce, as well as the smaller genera Cubanthus, Elaeophorbia, Endadenium, Monadenium, Synadenium,
and Pedilanthus were transferred to Euphorbia. The entire subtribe Euphorbiinae now consists solely of the genus Euphorbia.

Euphorbia has been extensively hybridised for garden use, with many cultivars available commercially. Moreover, some hybrid plants have been found growing in the wild, for instance E. × martini Rouy, a cross of E. amygdaloides × E. characias subsp. characias, found in southern France.