Nearly 30 years ago it was Alf who brought to my attention these patches of blue flowers that are frequently seen by the roadside in France and Spain. They are common chicory, a member of the dandelion family (it is also known as blue dandelion). The individual flowers are actually quite beautiful, they last but a short time, with new flowers appearing daily.
Roasted chicory root is used as a coffee substitute or additive, found in some types of French coffee. Interestingly, the salad leaf endive is of the same family, also sometimes known as chicory.