Plant Families with Succulent Species

Euphorbiaceae - Spurges

The Euphorbiaceae is a very large, widely distributed family including around 300 genera and 7700 species, mainly non-succulent herbs, shrubs and trees found in temperate, sub-tropical and tropical climates. Succulent species are found in the genera Euphorbia, Endadenium, Jatropha, Monadenium, and Pedilanthus, Phyllanthus, and Synadenium, although some of these genera are obsolete and their species now included under Euphorbia. Succulent Euphorbiaceae include diverse lifestyles including caudiciforms, stem succulents, shrubs and trees. Some species are very spiny, resembling Cactaceae at a first glance.

The Euphorbiaceae have very distinctive small cup-shaped compound flowers. The flower is technically known as a cyathium, consisting of a cup-like involucre containing a single pistil (female flower) surrounded by male flowers, each contributing a single stamen. The cyathium may be surounded by brightly coloured bracts that give the appearance of a large flower. However, some species of Euphorbia have separate male and female plants and some species e.g. Euphorbia obesa may produce a mixture of male, female and bisexual flowers.

Many species have a milky sap containing latex and irritant toxins including diterpene esters, alkaloids, glycosides, and ricin-type protein toxins, depending on the species. The latex should be washed off the skin without delay and eye contamination avoided at all costs.

Toxicity of Euphorbia latex

Euphorbia latex is commercially exploited, with Hevea brasiliensis (rubber tree) the main species grown in plantations throughout the tropics, especially Malaysia and SE Asia. Other important Euphorbiaceae include Ricinus communis (Castor Oil Plant) and Manihot esculenta (Cassava) cultivated for its starchy root and Euphorbia pulcherrima (Poinsettia) widely cultivated in the horticultural trade.

Cultivation: Most succulent Euphorbias require warmth and full to partial sun. Watering should be very sparing during the winter, especially for caudiciform species unless they can be kept warm and in growth. A very gritty compost suits most species, especially caudiciforms and those with fleshy roots. However, succulent Euphorbias, especially those with leaves, appreciate a dose of high nitrogen fertiliser at the start of their growing season. At other times a balanced fertiliser is suitable.

Euphorbia antisyphillitica

Jatropha dioica

Pedilanthus macrocarpus

Left: The candelilla plant (Euphorbia antisyphyllitica) growing at the Langtry visitor center, Texas. The epiphet antisyphyllitica refers to the plant's supposed medicinal properties. The flowers are relatively decorative by the standard of many Euphorbias. This plant is relatively common in the Big Bend country and the Rio Grande valley but in its natural habitat, where water may be scarce and the heat intense, the stems often have a bronzed appearance.

The candelilla plant was an important source of candelilla wax, which is still produced in small quantities by boiling large quantities of stems with sulphuric acid, and skimming the wax from the surface of the vat. The wax was used in the manufacture of phonograph records, in cosmetics and as an industrial lubricant.

Unfortunately, much of the plant material required for processing is harvested from its native habitat putting pressure on plant populations.

Left: Euphorbia clavarioides (lion's spoor) - a small caudiciform Euphorbia popular with growers of alpines. Native to mountains of Botswana and South Africa, growing at elevations of 4800-8800 ft. In the very strong light of its habitat, the arms are short and compact forming a hemispherical cushion. The loose growth habit shown here is typical of a plant cultivated at lower light levels. The plant will tolerate cool, frost free winter conditions. The sap may irritate the skin.

Photographed in the Alpine House at RBG Kew.

Left: Euphorbia suzanne - a small caput-medusae style Euphorbia from the Karoo, that makes a handsome specimen, given sufficient time. This plant has developed a cristate main head although it grew as a normal plant for many years.

In their habitat, the plants are sunk into the ground with the space between the main head and the side stems covered in grit or debris. However, plants in cultivation need to be raised to keep them healthy. This one is grown in diffuse sunlight behind other shrubby spurges.

Euphorbia suzanne tolerates a cool, frost-free winter provides it is kept dry. It should be planted in a very gritty mixture with plenty of crocking at the bottom of the pot.

Left: Dragon's blood, Leatherstem, Jatropha dioica, growing on limestone South of Shafter

		Left: Pedilanthus macrocarpus, (Slipper Plant) from Sonora and Baja California, growing in the Phoenix Desert Botanical Garden. The flowers attract humming birds. This species is an excellent plant for a container in a warm climate but will not stand any frost.
	Left: Pedilanthus tithymaloides (Devil's Backbone, Slipper Plant) is a tender climbing shrub native to Florida and the West Indies to Venezuela, but established as an invasive weed throughout the tropics. Young stems carry pointed oval leaves. This species is of interest as a potential biofuel crop, as it grows profusely on poor land.