Euphorbia milii var. splendens, or Crown of thorns, is a widely cultivated Euphorbia. It is a tough plant that withstands extreme conditions well. With red (or also yellow or pink) bracts, its stems are covered in stout, thickly set spines. These plants can be brought outdoors for the summer; to prevent sunburn, acclimate them gradually to the higher levels of light outdoors.
The following website provides additional information on the care and growing requirements of this beautiful houseplant: www.st-andrews.ac.uk/~gdk/stabg_new/poms/images/pom_pdf/nov05.pdf