Nerium oleander, the oleander, is a shrub or small tree native to the Mediterranean region east to southern Asia, from Morocco and Portugal east to India and Myanmar; the Flora of China also cites it as native in Yunnan in China. It is the only species currently classified in the genus Nerium, belonging to subfamily Apocynoideae of the dogbane family Apocynaceae. It is also cultivated widely in temperate and subtropical areas as an introduced ornamental and landscaping plant. It is tolerant to both drought and inundation, but not to prolonged frost. It is a highly poisonous plant but its bitterness renders it unpalatable to humans and most animals, so poisoning cases are rare and the general risk for human mortality is low. Ingestion of larger amounts may cause nausea, vomiting, excess salivation, abdominal pain, bloody diarrhoea and irregular heart rhythm. Prolonged contact with sap may cause skin irritation, eye inflammation and dermatitis.
Description
Oleander grows to 2–6 metres (7–20 feet) tall, with erect stems that splay outward as they mature; first-year stems have a glaucous bloom, while mature stems have a greyish bark. It is most commonly grown in its natural shrub form, but can be trained into a small tree with a single trunk. The leaves are in pairs or whorls of three, thick and leathery, dark-green, narrow lanceolate, 5–21 centimetres (2–8 inches) long and 1–3.5 cm (3⁄8–1+3⁄8 in) broad, and with an entire margin filled with minute reticulate venation web typical of eudicots. The leaves are light green and very glossy when young, maturing to a dull dark green. The flowers grow in clusters at the end of each branch; they are 2.5–3 cm (1–1 in) diameter, pink, with a deeply 5-lobed fringed corolla round the central corolla tube in natural wild plants. White to dark red, larger (to 5 cm diameter), and double-flowered, cultivars are also common in cultivation. 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.
Taxonomy Nerium oleander is the only species currently classified in the genus Nerium. It belongs to (and gives its name to) the small tribe Nerieae of subfamily Apocynoideae of the dogbane family Apocynaceae. The genera most closely related thus include the equally ornamental (and equally toxic) Adenium G.Don and Strophanthus DC., both of which also contain (like oleander) potent cardiac glycosides that have led to their use as arrow poisons in Africa. The three remaining genera Alafia Thouars, Farquharia Stapf and Isonema R.Br. are less well known in cultivation.
Synonymy The plant has been described under a wide variety of names that are today considered synonymous:
Etymology The taxonomic name Nerium oleander was first assigned by Linnaeus in 1753. The genus name Nerium is the Latinised form of the Ancient Greek name for the plant nẽrion (νήριον), which is in turn derived from the Greek for water, nẽros (νηρός), because of the natural habitat of the oleander along rivers and streams. The origins of the species name are disputed. The word oleander appears as far back as the first century AD, when the Greek physician Pedanius Dioscorides cited it as one of the terms used by the Romans for the plant. Merriam-Webster believes the word is a Medieval Latin corruption of Late Latin names for the plant: arodandrum or lorandrum, or more plausibly rhododendron (another Ancient Greek name for the plant), with the addition of olea because of the superficial resemblance to the olive tree (Olea europaea) Another theory posited is that oleander is the Latinised form of a Greek compound noun: οllyo (ὀλλύω) 'I kill', and the Greek noun for man, aner, genitive andros (ἀνήρ, ἀνδρός). ascribed to oleander's toxicity to humans. The etymological association of oleander with the bay laurel has continued into the modern day: in France the plant is known as "laurier rose", while the Spanish term, "Adelfa", is the descendant of the original Ancient Greek name for both the bay laurel and the oleander, daphne, which subsequently passed into Arabic usage and thence to Spain. The ancient city of Volubilis in Morocco may have taken its name from the Berber name alili or oualilt for the flower. It is also sometimes known as rose laurel, be-still tree or rosebay,
Distribution and habitat
Nerium oleander is either native or naturalised to a broad area from northwest Africa through the Mediterranean region and warmer areas of the Black Sea region, Arabian Peninsula, southern Asia, and as far east as Yunnan in southern parts of China. It can be found in tropical, subtropical, and temperate regions. The plant typically occurs in dry locations with a lot of sun near stream beds where it can alternatively tolerate long seasons of drought and inundation from winter rains.
Ecology Some invertebrates are known to be unaffected by oleander toxins, and feed on the plants. 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 fibres. 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 such as spiders and wasps. The flowers require insect visits to set seed, and seem to be pollinated through a deception mechanism. The showy corolla acts as a potent 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 typical of many rewardless flower species. Fears of honey contamination with toxic oleander nectar are therefore unsubstantiated.
Leaf scorch
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