Crown of thorns is a rather odd looking plant, but I think it is my favourite plant in the genus Euphorbia, which is named after Greek Euphorbus as an honour to the doctor of Juba the second, as this doctor supposedly used a plant with milk sap that also had strong medicinal qualities. The ‘milii’ part of the name is in honour of one Baron Milius who took this species into France for the first time in 1821. While there are several common names for this plant, the name ‘crown of thorns’ comes from a legend that it was used worn as a crown by Jesus during his crucifixion, although this was more likely to be a different plant (you can’t be sure about much from so long ago with material that rots down quickly).

Crown of thorns is a native plant to the island of Madagascar. This shrub can reach a height of about one metre tall. Stems are brown, have between five and seven stems and are adapted to store water. These same stems are a nightmare as they are covered in spines that are 2.5 cm long. Some clones are now apparently nearly thornless.

The succulent leaves are narrow and ovate, to about 3 cm long, arranged spirally on the stem. They are green-grey and drop off the stem as it matures, giving it a very untidy look. Stress can cause the defoliation of the plant.

The flowers are typical of those in this genus and will appear throughout the year if it has the right conditions. Fused bracts (coloured leaves, think of those on the bougainvillea and you get the drift, just a different shape) form a cup around the single female flower that is surrounded by five male flowers and five nectar glands (two of which have the appearance of a flower). The species flower colour is actually yellow, the bracts are red, but there are many cultivars with other colours, including white and cream. Flowers can be in axillary cymes (an inflorescence where the central flowers open first) or sometimes terminal. Too much light around at night can cause the crown of thorns to flower poorly-darkness is required for flowering to be initiated.

Full sun is preferred, although they can deal with partial shade. They like low humidity, so allow the soil to dry out before watering again. The plants have a sensitivity to boron, which causes leaf chlorosis (where the leaves turn yellowish between leaf veins), followed by scorching and leaf drop of leaves on the interior of the plant. This plant needs a minimum of seven degrees Celsius.

As a word of caution, the sap of this plant is irritating, so if you need to prune it, do wear gloves and eye protection to prevent any damage.

Here in Australia, I don’t see this plant very often at all. Even though it is a scruffy little plant, I do quite like it-it’s a little prickly, tatty in an almost dead sort of way and has a party piece in its flowers, as you can see in the photo above.