This is a cristata form of Euphorbia ammak
Description: Euphorbia ammak is a striking Euphorbia of massive stature.
Flowers: Yellow-green, approx. 1 cm in diameter, fleshy.
It is an easy species to grow that is suited for any well-drained soil in full sun. But young plants are happy growing indoors, where they can easily reach the ceiling. Water regularly during the active growing season from March to September. No water should ever be allowed to stand around the roots. Keep almost completely dry in winter.
Some of the information in this description has been found at desert-tropicals.com, llifle.com and cactus-art.biz
