Something I find fascinating about Joshua trees (besides the fact that like tree ferns they're not trees at all) is the way they embody mathematical binary trees so naturally: they go straight for a while, then they bifurcate, then straight a while again, etc. I think I've heard that they tend towards being complete binary trees, because the branches are all likely to bifurcate at the same time, but that was obviously not true of all the trees I saw. It's a phenomenon that's easier to see in the smaller trees that have only branched a few times, rather than the big tangled ones. I tried to capture some of that in my photos, but I don't think I really succeeded.
The rest of the gallery.