About Nerium oleander L.
Oleander (Nerium oleander L.) grows 2–6 metres (7–20 feet) tall, with erect stems that spread outward as they mature. First-year stems have a glaucous bloom, while mature stems have grayish bark. Leaves are produced in pairs or whorls of three; they are thick and leathery, dark-green, and narrow lanceolate, 5–21 centimetres (2–8 inches) long and 1–3.5 cm (3⁄8–1+3⁄8 in) broad, with an entire margin covered in minute reticulate venation, a pattern typical of eudicots. Young leaves are light green and very glossy, maturing to a dull dark green. Flowers grow in clusters at the end of each branch; they can be white, pink to red, and reach 2.5–5 cm (1–2 in) in diameter, with a deeply 5-lobed fringed corolla surrounding a central corolla tube. They are often, but not always, sweet-scented. The fruit is a long narrow pair of follicles 5–23 cm (2–9 in) long, which splits open at maturity to release numerous downy seeds. Nerium oleander is either native or naturalized across a broad range extending from northwest Africa through the Mediterranean region, warmer areas of the Black Sea region, the Arabian Peninsula, and southern Asia, as far east as Yunnan in southern China. It typically grows around stream beds in river valleys, and it can tolerate both long drought seasons and inundation from winter rains. N. oleander is planted in many subtropical and tropical areas of the world. On the East Coast of the United States, it grows as far north as Virginia Beach, while in California and Texas, miles of oleander shrubs are planted on highway median strips. It is estimated that 25 million oleanders are planted along highways and roadsides throughout California. Due to its durability, oleander was planted prolifically on Galveston Island in Texas after the disastrous 1900 Hurricane. They are so common there that Galveston is known as the 'Oleander City', and hosts an annual oleander festival every spring. Moody Gardens in Galveston hosts the propagation program for the International Oleander Society, which promotes oleander cultivation. New varieties are hybridized and grown on the Moody Gardens grounds, covering every named variety. Outside its traditional Mediterranean and subtropical range, oleander can also be cultivated in mild oceanic climates with appropriate precautions. It is grown without protection in warmer areas of Switzerland, southern and western Germany, and southern England, and can reach large sizes in London, and to a lesser extent in Paris, due to the urban heat island effect. This is also true for North American cities in the Pacific Northwest such as Portland, Seattle, and Vancouver. Plants may suffer damage or die back in these marginal climates during severe winter cold, but will regrow from the roots. Some invertebrates are unaffected by oleander toxins and feed on the plant. Caterpillars of the polka-dot wasp moth (Syntomeida epilais) feed specifically on oleanders, and survive by eating only the pulp surrounding the leaf veins, avoiding the fibers. Larvae of the common crow butterfly (Euploea core) and oleander hawk-moth (Daphnis nerii) also feed on oleanders, and they retain or modify toxins, making them unpalatable to potential predators such as birds, but not to other invertebrates like spiders and wasps. The flowers require insect visits to set seed, and appear to be pollinated through a deception mechanism. The showy corolla acts as a strong advertisement to attract pollinators from a distance, but the flowers are nectarless and offer no reward to their visitors. They therefore receive very few visits, as is typical of many rewardless flower species. Fears of honey contamination with toxic oleander nectar are therefore unsubstantiated. Oleander is a poisonous plant due to toxic compounds it contains, especially when consumed in large amounts. These compounds include oleandrin and oleandrigenin, which are cardiac glycosides with a narrow therapeutic index that are toxic when ingested. Side effects after ingestion include weakness, diarrhoea, nausea, vomiting, headache, stomach pain, and death. Toxicity studies in animals found that birds and rodents are relatively insensitive to administered oleander cardiac glycosides. Other mammals, however, such as dogs and humans, are relatively sensitive to the effects of cardiac glycosides and the clinical manifestations of glycoside intoxication. It is also hazardous to grazing animals including sheep, horses, and cattle; as little as 100 g is enough to kill an adult horse. Plant clippings are especially dangerous to horses, as they are sweet. In July 2009, several horses were poisoned this way from the plant's leaves. Symptoms of a poisoned horse include severe diarrhea and an abnormal heartbeat. This is reflected in the plant's Sanskrit name aśvamāra (अश्वमार), a compound of aśva 'horse' and māra 'killing'. In a review of in-hospital oleander toxicity cases, Lanford and Boor concluded that, except for children who may be at greater risk, the human mortality associated with oleander ingestion is generally very low, even in cases of moderate intentional consumption (suicide attempts). In 2000, a rare fatal instance of oleander poisoning occurred when two toddlers adopted from an orphanage ate leaves from a neighbor's shrub in El Segundo, California. Because oleander is extremely bitter, officials speculated that the toddlers had pica, a condition caused by malnutrition that makes people eat otherwise inedible material. Ingestion of this plant can affect the gastrointestinal system, the heart, and the central nervous system. The main effect of cardiotoxic glycosides is positive inotropy. Glycosides bind to the sarcolemma transmembrane ATPase of cardiac muscle cells and compete with K+ ions, inactivating the enzyme. This results in accumulation of Na+ and Ca2+ ions inside cardiac muscle cells, leading to stronger and faster heart contractions. Additionally, increased extracellular K+ ions may lead to lethal hyperkalemia. Clinical features of oleander poisoning are therefore similar to digoxin toxicity, and include nausea, diarrhea, and vomiting from stimulation of the area postrema of the medulla oblongata, plus neuropsychic disorders and pathological motor manifestations. Cardiotoxic glycosides also stimulate the vagus nerve (causing sinus bradycardia) and the phrenic nerve (causing hyperventilation), and can lead to lethal bradyarrhythmias and tachyarrhythmias, including asystole and ventricular fibrillation. Oleander poisoning can also cause blurred vision and other vision disturbances, including halos around objects. Oleander sap can cause skin irritations, severe eye inflammation and irritation, and allergic reactions that present as dermatitis. The severity of intoxication varies based on the quantity ingested, an individual's physiological response, and the timing of symptom onset after ingestion: symptoms can appear rapidly after drinking teas made with oleander leaves or roots, or develop more slowly after ingestion of unprepared plant parts.
