Common Blue Violet

according to wikipedia:
'Beyond its use as a common lawn and garden plant, Viola sororia has historically been used for food and for medicine. The flowers and leaves are edible, and some sources suggest the roots can also be eaten. The Cherokee used it to treat colds and headaches. Rafinesque, in his Medical Flora, a Manual of the Medical Botany of the United States of North America (1828–1830), wrote of Viola sororia being used by his American contemporaries for coughs, sore throats, and constipation."
http://procezzed.blogspot.com/2012/02/common-blue-violet-viola-sororia…