Hi Pyrocat,
I can't quite tell from the picture, but it appears to be Senecio rowleyanus aka string of pearls aka string of beads.* This plant is highly toxic to pets and small children, so you will have to be diligent about cleaning up any dropped bits if you have pets or young kids.
http://www.plantstogrow.com/zPlantsD...p?plantID=1036
Newt
When weeding, the best way to make sure you are removing a weed and not a valuable plant is to pull on it. If it comes out of the ground easily, it is a valuable plant.