Oleander (Nerium oleander) is a highly ornamental evergreen shrub, widely cultivated in warm climates for its showy, fragrant clusters of flowers which can be white, pink, red, or yellow. Despite its beauty, from a botanical and toxicological perspective, it is crucial to understand that this plant has evolved a potent chemical defense system. Every morphological part of the oleander plant contains toxic compounds, making it one of the most poisonous commonly grown garden plants.
The toxicity of the oleander plant is not localized to a specific organ like seeds or berries; it is systemic. This means the poisonous compounds are synthesized and transported throughout the entire vascular system of the plant. Therefore, all parts, including the leaves, stems, flowers, sap, and even the roots, contain these toxic agents. This comprehensive defense mechanism protects the plant from herbivores and insects. The primary toxins are cardiac glycosides, such as oleandrin and nerioside, which are highly stable and retain their potency even in dried plant material.
The concentration of cardiac glycosides can vary between different parts of the plant and may be influenced by factors like the plant's cultivar, age, and growing conditions. However, no part is considered safe.
Leaves: The leaves contain a very high concentration of cardiac glycosides. They are the most common source of poisoning incidents, particularly in livestock and curious children. Ingesting even a single leaf can be potentially fatal to a human or a small animal.
Stems and Sap: The stems contain the same toxins as the leaves. The milky sap is especially potent and can cause severe skin irritation and dermatitis upon contact for some individuals, as well as eye irritation. Using the stems as skewers for food is extremely dangerous, as the toxins can leach into the food.
Flowers: The beautiful and fragrant flowers are also toxic. While their nectar is poisonous, the primary risk from the flowers is the same as from the leaves: ingestion. The bright colors can be attractive to children, posing a significant hazard.
Roots and Seeds: The root system and the seeds of the oleander plant are equally poisonous. While less likely to be encountered casually, they represent no less of a toxic threat if ingested.
The cardiac glycosides in oleander function by disrupting the electrolyte balance within heart muscle cells. They inhibit the sodium-potassium pump, a critical enzyme system, leading to an increase in intracellular calcium. This disruption causes severe cardiac effects, including potentially fatal arrhythmias. Symptoms of oleander poisoning can include nausea, vomiting, abdominal pain, diarrhea, dizziness, visual disturbances, an irregular or slowed heartbeat, and in severe cases, death.
