Trachelium caeruleum subsp. caeruleum

Tutin, T. G., Heywood, V. H., Burges, N. A., Moore, D. M., Valentine, D. H., Walters, S. M. & Webb, D. A., 1976, Flora Europaea. Volume 4. Plantaginaceae to Compositae (and Rubiaceae), Cambridge University Press : 94

(a) Subsp. caeruleum :

Leaves ovate to broadly lanceolate, with acute, ciliolate teeth; petioles not winged. In = 32. Throughout the range of the species.