u/H4ppyM3al

My guess is it's swiss meringue to make it more stable for piping, perhaps it it baked / hardened as separate pieces for the white base and the cactus then glued together with raw meringue and baked again.

But what about the taller cactus? How are the limbs being attached? Are they made flat so the back that we don't see in the picture is not textured all around?