This lovely pincushion Euphorbia is not meloformis, which has much fewer stems and distinct spines, among other differences. See that database listing here:

Melon Spurge (Euphorbia meloformis)

I will move this image to the genus listing for Euphorbia. If anybody knows a species name which properly applies, we can move it to a more specific listing. Any comments or disagreement just say the word.

Thanks Baja for correcting this. I might be able to provide some more info - may or may not be helpful. In the photo of the mystery plant, there is a white ID tag just above the plant. I can't read it to know if it might be a clue to its identity. I tried enlarging the original photo but I still can't make out the name. I'm not sure it will turn out to have anything to do with the plant's ID but it might be recognizable by someone who knows more about euphorbias than me. (I also include the label which was the one I used to incorrectly identify the plant originally.)

Best I can tell (sort of guessing) the white sign reads Hamatocactus sp., which would presumably apply to some nearby cactus. Name tags do wander astray sometimes in bot gardens.