Origin and Habitat: Garden origin (Nursery produced cultivar)

• Euphorbia horrida f. cristata hort.

• Euphorbia horrida Boiss.
• Euphorbia horrida var. gigas hort., Lavranos

Description: Euphorbia horridaSN|21536]]SN|13381]] is a spiny succulent shrub with irregular basally clumping stems. In age it will forms tight clumps of upright columns up to a metre wide that closely resemble some cactus species. It also has clustered crowns of somewhat ferocious spines much like the true cacti. The crested form Euphorbia horridaSN|13381]]SN|13381]] f. cristata - despite to its beauty - is still very rare and sought after by collectors, for its unique features. There are several clones in cultivation with stems ranging from white to grey-green and with or without spines.
Stem: Fan shaped, flattened on top, depressed centrally 3 to 12 cm thick, blue-grey to grey-green and often with white stripes.
Ribs: Wing-like, prominent, deeply grooved between and more or less undulated
Spines: On the ribs there are 1-5 persistent peduncles, spiny and crowded together about 4-10 mm long and 1-4 formidable main spines up to 40 mm long and very rigid.
Leaves: Inconspicuous and ephemeral in the centre of the plant.
Peduncles: Solitary 4-8 mm tall, hairy with small bracts.
Flowers: Very small green-yellow solitary cyathia approx 4 mm in diameter. Involucre finely hairy with 5 glands and 5 large lobes. Pistil three-lobed. Involucres glands are green, blooms in summer.
Remarks: This plant is somewhat variable with many varieties and forms, and perhaps natural hybrids between it and taller Euphorbias, giving rise to the big, spiny forms like Euphorbia horridaSN|21536]]SN|13381]] var. noorvalescens, furthermore there are several other similar Euphorbia species (particularly Euphorbia polygonaSN|21536]]SN|21536]]) which often looks a lot like some of the forms. Euphorbia horrida and Euphorbia polygonaSN|13381]]SN|21536]] are hard to tell apart only by body characteristics, at least when the plants are young. The only certain characteristic is in their cyathia. Euphorbia horridaSN|13381]]SN|13381]] bears green cyathia that sometimes may turn brownish with the age. The cyathia of Euphorbia polygonaSN|13381]]SN|21536]] are red to deep purple.
Parasites: E. horrida is the suitable host plant for the charming parasite Viscum minimum (mistletoe). A minute monoecious, parasitic plant that grows profusely within the stem of the host. Viscum minimum is one of the few types of mistletoe that is ever cultivated outside of its native land. It doesn’t cause significant harm to its host plant, and will produce crops of colourful fruit in time for the holidays year after year.

Bibliography: Major references and further lectures
1) Urs Eggli "Illustrated Handbook of Succulent Plants: Dicotyledons" Springer, 2002
2) John Manning, Colin Paterson-Jones "Southern African Wild Flowers: Jewels of the Veld" Struik, 2004
3) Hermann Jacobsen "A handbook of succulent plants: Abromeitiella to Euphorbia" Blandford Press, 1960
4) David Rogers "Southern Africa" Struik, 2006
5) Alain Campbell White, Robert Allen Dyer, Boyd L. Sloane "The succelent Euphorbisae (southern Africa)" Abbey garden press, 1941
6) Maurizio Sajeva, Mariangela Costanzo "Succulents 2" Timber Press, 15/mar/2000
7) EUPHORBIA horrida Boiss. [family EUPHORBIACEAE] in: "Flora Capensis", Vol 5 Part 2, page 216 (1925) Author: (By N. E. BROWN, J. HUTCHINSON and D. PRAIN.)

Cultivation and Propagation: It is not too difficult in a greenhouse, although grows quite slowly. It is usually seen as a grafted plant but can grow on its own roots too.
Soil: Use a mineral well permeable soil with little organic matter (peat, humus).
Exposure: They need a good amount of light shade to full sun this help to keep the plants healthy, although slow growth.
Watering: Water sparingly from March till October (weekly during summertime, if the weather is sunny enough), with a little fertilizer added. Less or no water during cold winter months, or when night temperatures remain below 10° to prevent root loss. It is sensitive to overwatering (rot prone).
Fertilization: Feeding may not be necessary at all if the compost is fresh then, feed in summer only if the plant hasn't been repotted recently. Do not feed the plants from September onwards as this can cause lush growth which can be fatal during the darker cold months.
Hardiness: Keep perfectly dry in winter at temperatures from 5 to 15 degrees centigrade. (but it is relatively cold resistant and hardy to -5° C, or possibly colder for short periods) In the rest period no high atmospheric humidity!! (Temperature Zone: USDA 9-11)
Crested growth: Unlike 'monstrose' varieties of plants, where the variation from normal growth is due to genetic mutation, crested growth can occur on normal plants. Sometimes it's due to variances in light intensity, or damage, but generally the causes are unknown. A crested plant may have some areas growing normally, and a cresting plant that looks like a brain, may revert to normal growth for no apparent reason. If you have any of the crested part left you need to remove the normal growth and leave the crested part behind this will need to be done regularly.
Propagation: Grafting or cuttings. Plants are usually grafted onto column-shaped cacti but proved to be able to produce their own roots if degrafted. Cuttings will take root in a minimum temperature of 20° C (but better in hot weather). Cuttings of healthy shoots can be taken in the spring and summer. Cut the stem with a sharp, sterile knife, leave the cutting in a warm, dry place for a week or weeks (depending on how thick the cutting is) until a callus forms over the wound. Once the callus forms, the cutting may be inserted in a container filled with firmed cactus potting mix topped with a surface layer of coarse grit. They should be placed in the coarse grit only; this prevents the cut end from becoming too wet and allows the roots to penetrate the rich compost underneath. The cuttings should root in 2 to 6 weeks. Large crested piece must be placed on the soil surface without burying the plant base down in the soil.