Hi Jenn,

I certainly can't give you a definite ID as to species, but I *think* it may well be in the Euphorbia family. As you may well know, this is a hugely diverse group with various spurges, poinsettia & crown-of-thorns being some of the representatives. The leaves (and to a much lesser extent) of the last remind me a bit of your plant. I stress, though, I'm far from certain. Does it ever flower? Flowers are better for plant ID than just the leaves & stems.

Cheers,

Rob