Looks like a grafted form of Euphorbia lactea f. cristata, sold under the common name of Elkhorn or Fan Euphorbia.

I believe it is Myrtillocactus geometrizans f. cristata.

Thank you !

Just to confuse the name game a bit more, there is a look-a-like wanna be, Euphorbia kibweaensis. I guess one could take sharp knife and poke it. If it bleeds white stuff then a Euphorbia but since I am unfamiliar with Rosemarie's choice this may not work....

This is definitely a cactus, you can tell by the spines, so no need to poke it.

Christopher