Reference
Herwig Teppner (2011): Flowers of Boraginaceae (Symphytum, Onosma, Cerinthe) and Andrena symphyti (Hymenoptera - Andrenidae): Morphology, Pollen, Portioning, Vibratory Pollen Collection, Nectar Robbing – Phyton, Annales Rei Botanicae, Horn – 50_2: 145 - 180.