The Crown of Thorns

Zizyphus spina Christi, or the jujube tree.

he bushes, from which the Crown of Thorns was made, grew, and still grow abundantly, in the outskirts of Jerusalem. The monks of St. Catherine Monastery in Sinai have identified a thorn bush growing east of the large monastery wall as the same original Crown of Thorns.
With regard to the origin and character of the thorns, both tradition and existing remains suggest that they must have come from the bush botanically known as Zizyphus spina Christi, more popularly, the jujube tree. This reaches the height of fifteen or twenty feet and is found growing in abundance by the wayside around Jerusalem. According to Dr. G. E. Post, who is an expert on these matters, this plant grows in the region of old Jerusalem, especially in the area where Golgotha (or place of the Crucifixion) is said to have been. The crooked branches of this shrub are armed with thorns growing in pairs, a straight spine and a curved one commonly occurring together at each point.  Application of the powdered leaves is said to darken and lengthen women's hair.

Other sources refer to the thorns as either of two nearly leafless, very spiny shrubs or small trees of the southwestern North American deserts. Koeberlinia spinosa, with green thorns at right angles to the branches, produces small, four-petaled, greenish flowers and clusters of black berries. Another source says it could be Euphorbia milii.