Reference

Tea A. Jaarsma, Elisabeth Lohmanns, H. Hendriks, Th. W. J. Gadella, Theo M. Malingré (1990): Chemo- and karyotaxonomic studies on some rhizomatous species of the genus Symphytum (Boraginaceae) – Österreichische Botanische Zeitschrift = Plant Systematics and Evolution – 169: 31 - 39.