This is a low sprawling evergreen to deciduous shrub has squarish succulent stems that are covered in thorns. It has oblong bright green leaves and the tiny flowers are accompanied with large orange scarlet bracts that appear from spring to summer.

Hardiness zones 10 to 12

E. milii var. splendens is naturally found in Madagascar growing in very well drained, moderately fertile sandy-stony soils in an open sunny position and is frost tender but drought resistant. 

The Crown of Thorns is grown for its colourful bracts and spreading habit. It is planted in rockeries or arid gardens as a specimen or along borders as a barrier plant. It is suitable for coastal regions and establishes in 3 to 5 years requiring little maintenance. It is also grown in containers or used in roof gardens, tolerating exposed positions. ID 154
  
Note:
Care should be taken as the milky sap may produce severe dermatitis in susceptible individuals and the plant has very sharp spines. 

Euphorbia (yoo-FOR-bee-a) milii (MIL-ee-eye)

E. milii var Lutea
This plant has larger leaves and yellow-red bracts.
‘Euphorbia’: after Euphorbus, physician to Juba, King of Mauritius; ‘milii’: thousands (referring to the profusion of flowers).

Euphorbiaceae (yoo-for-bee-AY-see-ee)
Spurge Family