Polygala amarella
Polygala amarella (or P. amara), commonly known as dwarf milkwort or Kentish milkwort, is a plant of the family Polygalaceae. A European native, it grows on chalky grass land and limestone mountain pastures. Description 
The plant typically grows up to 20 cm tall and has small, blue-purple flowers that bloom from May to August. The leaves are alternate, narrow, and smooth-edged, and the stems are slender and wiry. Uses 
Polygala amarella has traditionally been used in herbal medicine. In media 
In 2009 it featured on a first class Royal Mail stamp in the series "Endangered Plants". References

amarella
Flora of Europe