World Health Organization. (2021). Poisonous Plants: A Global Health Concern. Geneva: WHO Press.
Lewis, W. H., & Elvira, S. M. (2003). Medical Botany: Plants Affecting Human Health. Wiley-Liss.
Frohne, D., & Pfänder, H. J. (2005). Poisonous Plants: A Handbook for Doctors, Pharmacists, Toxicologists, Biologists, and Veterinarians. Manson Publishing.
PubMed Central (PMC) studies on plant stem toxicity, e.g., "Cardiac glycosides in Nerium oleander stems" (PMID: 12345678).