This species is considered to be native to Spain, the Balearic Islands, and Morocco east through Mediterranean coastal countries to the Arabian Peninsula, Ethiopia, Niger, Afghanistan, Iran and Iraq to India and central China. It occurs as a non-native in parts of Africa, the Azores, Japan, Indonesia, Australia, New Zealand, the United States, central and eastern Mexico, Central and South America.
This species is very widely cultivated as an ornamental. All parts of the plant are poisonous and so it is not grazed or eaten. Steam from boiled leaves is inhaled to relieve sinusitis, pounded leaves are applied to the skin to relieve itching, ulcers and tumours (Jongbloed 2003); the leaves are used as an insecticide.
Undoubtedly a candidate for the most poisonous plant in the garden but also a contender for most beautiful.
Oleander grows to 2–6 m (6.6–19.7 ft) tall, with erect stems that splay outward as they mature; first-year stems have a glaucous bloom, while mature stems have a grayish bark. The leaves are in pairs or whorls of three, thick and leathery, dark-green, narrow lanceolate, 5–21 cm (2.0–8.3 in) long and 1–3.5 cm (0.39–1.38 in) broad, and with an entire margin.
The flowers grow in clusters at the end of each branch; they are white, pink to red,[Note 2] 2.5–5 cm (0.98–1.97 in) diameter, with a deeply 5-lobed fringed corolla round the central corolla tube. They are often, but not always, sweet-scented.[Note 3] The fruit is a long narrow capsule 5–23 cm (2.0–9.1 in) long, which splits open at maturity to release numerous downy seeds.