Euphorbia milii

Euphorbia milii, known in English as "crown of thorns", "Christ plant", or "Siamese lucky plant", and in French as couronne d'épines, couronne de Christ, or épine de Christ, is a viciously thorny shrub native to Madagascar. The small flowers are surrounded by red, pink, or white bracts.

This is another tropical which is nowhere near hardy enough to grow in Toronto, except as a houseplant or better still in a greenhouse (this one's in the Allan Gardens conservatory). Because it's poisonous and the thorns would be hard to live with, I think I'll just admire it from afar.