Posted: 05/06/2016 at 15:43
It's Caper spurge, a wild type of euphorbia (E. lathyris.) They appear from nowhere, probably as a result of bird droppings.
Watch the white milky sap if you break a stem or decide to remove it as it causes a photo-sensitive reaction on the skin.
Last edited: 05 June 2016 15:44:47