H.G.L. Reichenbach, Icon. Fl. Germ. Helv., vol. 17 (Die Gentianaceen, Apocynaceen, Asclepiadeen, Oleaceen, Styracaeen, Ebenaceen, Aquifoliaceen, Primulaceen, Plumbagineen, Bicornes, Caprifoliaceen, Rubiaceen der deutschen Flora
): t. 1086, fig. 1 (1855) [H.G. Reichenbach] [410]