Cypress Spurge

I don't trust myself a lot so 99,9% sure. :D

As I told you and before euphorbias are quite various. You are comparing them by the tallness but that isn't quite right, because how big one plant will grow depends on the plant hormones, how much water it gets, how much sun it needs and so on and so on. Yes, the young stems are without branches, but when the flowers on the central flower stalk fade away (you know that the orange leaves aren't part of the blossom, right) the leaves get old and the plant gets branchy with sterile or new-flowers-bearing stems. If why you see some young and old euphorbias in the same time is bothering you, that is because some started developing more earlier than others, or some are bigger than others and they need more time to fully grow. If that doesn't answer you, there is a huge chance that I haven't understood the question. :D :D :D

I have huge doubts that this in the link is really cyparissias, or at least the wild type, could be some cultivar, don't know. (Edit: Nope, it's different species, post it as a comment in the link) The orange color in yours shows that the flower stalk is old already, and when this happen it gets branchy. :) http://www.treknature.com/gallery/photo150080.htm

Ambroise.baker is right, I think it's cyparissias too. :)