Symphytum x uplandicum - Description of Russian Comfrey and two photographs. - http://www.plant-identification.co.uk/skye/boraginaceae/symphytum-x-uplandicum.htm
Symphytum tuberosum - Several photographs of Tuberous Comfrey and some identifying features. - http://www.plant-identification.co.uk/skye/boraginaceae/symphytum-tuberosum.htm