ŠUŠEK, Andrej. Helleborus Niger: Systematics, Ecology, Pollination and Production Technology. [s.l.] : University of Maribor Press,2021. DOI: 10.18690/978-961-286-483-5. Disponível em: https://old.press.um.si/index.php/ump/catalog/book/580. Acesso em: 28 feb. 2026.