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).

[6] It has a unique kind of pseudanthium, called a cyathium, where each flower in the head is reduced to its barest essential part needed for sexual reproduction.

[6] The common name "spurge" derives from the Middle English/Old French espurge ("to purge"), due to the use of the plant's sap as a purgative.

The botanical name Euphorbia derives from Euphorbos, the Greek physician of King Juba II of Numidia and Mauretania (52–50 BC – 23 AD), who married the daughter of Anthony and Cleopatra.

[11] In 1753, botanist and taxonomist Carl Linnaeus assigned the name Euphorbia to the entire genus in the physician's honor.

[12] The plants are annual, biennial or perennial herbs, woody shrubs, or trees with a caustic, poisonous milky latex.

The main stem and mostly also the side arms of the succulent species are thick and fleshy, and often winged, 15–91 cm (6–36 in) tall.

The involucre is above and supported by bract-like modified leaf structures (usually in pairs)[citation needed] called cyathophylls', or cyathial leaves.

[14] The cyathophylls often occur in twos, are leaf-like, and may be showy and brightly coloured and attractive to pollinators, or be reduced to barely visible tiny scales.

[citation needed] The fruits are three- or rarely two-compartment capsules, sometimes fleshy, but almost always ripening to a woody container that then splits open, sometimes explosively.

[16] In contact with mucous membranes (eyes, nose, mouth), the latex can produce extremely painful inflammation.

A physician should be consulted if inflammation occurs, as severe eye damage including permanent blindness may result from exposure to the sap.

[18] The poisonous qualities were well known: in the Ethiopian Kebra Nagast, the serpent king Arwe is killed with juice from the Euphorbia.

[6] Morphological description using the presence of a cyathium (see section above) is consistent with nuclear and chloroplast DNA sequence data in testing of about 10% of its members.

This testing supports inclusion of formerly other genera as being best placed in this single genus, including Chamaesyce, Monadenium, Pedilanthus, and poinsettia (E. pulcherrima).

The genetic data show that within the genus, convergent evolution of inflorescence structures may be from ancestral subunits that are not related.

As stated on the Euphorbia Planetary Biodiversity Inventory project webpage:[6] Previous morphologically based delimitations of subgenera or sections within the genus should not be taken at face value.

Consequently, these taxa, namely the never generally accepted genus Chamaesyce, as well as the smaller genera Cubanthus,[25] Elaeophorbia, Endadenium, Monadenium, Synadenium, and Pedilanthus were transferred to Euphorbia.

Moreover, some hybrid plants have been found growing in the wild, for instance E. × martini Rouy,[31] a cross of E. amygdaloides × E. characias subsp.