I was wondering what these white flowering clumps were growing between rows of trees. Capers! Neither fruit nor seed but the bud of a thorny, low growing flowering shrub. Caper picking is an arduous manual task taking place in the hottest months from June to September.
If you can find them packed in sea salt, they are supposed to be at their most flavoursome (once rinsed thoroughly) but you’ll more often see capers pickled in vinegar or brine. Here’s a good Huffington Post link to cooking with capers.