Nerium oleander (/ˈnɪəriəm .../NEER-ee-əm),[2] commonly known asoleander orrosebay,[3] is a shrub or small tree cultivated worldwide in temperate and subtropical areas as an ornamental and landscaping plant. It is theonly species currently classified in the genusNerium, belonging to subfamilyApocynoideae of thedogbane familyApocynaceae. It is so widely cultivated that no precise region of origin has been identified, though it is usually associated with theMediterranean Basin.
Nerium grows to 2–6 metres (7–20 feet) tall. It is most commonly grown in its natural shrub form, but can be trained into a small tree with a single trunk. It is tolerant to both drought and inundation, but not to prolonged frost. White, pink or red five-lobed flowers grow in clusters year-round, peaking during the summer. The fruit is a long narrow pair of follicles, which splits open at maturity to release numerous downy seeds.
Nerium is apoisonous 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 diarrhea and irregular heart rhythm. Prolonged contact with sap may cause skin irritation, eye inflammation anddermatitis.
Detail of the candy-striped corona and feathery style of a single peach-colored flower
Oleander grows to 2–6 metres (7–20 feet) tall, with erect stems that splay outward as they mature; first-year stems have aglaucous bloom, while mature stems have a grayish bark. Theleaves are in pairs orwhorls of three, thick and leathery, dark-green, narrowlanceolate, 5–21 centimetres (2–8 inches) long and 1–3.5 cm (3⁄8–1+3⁄8 in) broad, and with an entiremargin filled with minute reticulate venation web typical ofeudicots. 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 white, pink to red,[Note 1] 2.5–5 cm (1–2 in) diameter, with a deeply 5-lobed fringedcorolla round the centralcorolla tube. They are often, but not always, sweet-scented.[Note 2] The fruit is a long narrow pair offollicles 5–23 cm (2–9 in) long, which splits open at maturity to release numerous downy seeds.
Nerium oleander is the only species currently classified in the genusNerium. It belongs to (and gives its name to) the small tribeNerieae of subfamilyApocynoideae of the dogbane familyApocynaceae. The genera most closely related thus include the equally ornamental (and equally toxic)AdeniumG.Don andStrophanthusDC. - both of which contain (like oleander) potentcardiac glycosides that have led to their use asarrow poisons in Africa.[4] The three remaining generaAlafiaThouars,FarquhariaStapf andIsonemaR.Br. are less well known in cultivation.
Thetaxonomic nameNerium oleander was first assigned byLinnaeus in 1753.[7] The genus nameNerium is theLatinized form of theAncient Greek name for the plantnẽrion (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.[citation needed]
The origins of the species name are disputed. The wordoleander appears as far back as the first century AD, when the Greek physicianPedanius Dioscorides cited it as one of the terms used by the Romans for the plant.[8]Merriam-Webster believes the word is aMedieval Latin corruption ofLate Latin names for the plant:arodandrum orlorandrum, or more plausiblyrhododendron (another Ancient Greek name for the plant), with the addition ofolea because of the superficial resemblance to theolive tree (Olea europea)[Note 3][9][10] Another theory posited is thatoleander is the Latinized form of a Greek compound noun:οllyo (ὀλλύω) 'I kill', and the Greek noun for man,aner, genitiveandros (ἀνήρ, ἀνδρός).[11] ascribed to oleander's toxicity to humans.
The etymological association ofoleander with thebay laurel has continued into the modern day: in France the plant is known as "laurier rose",[12] 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 intoArabic usage and thence to Spain.[13]
The ancient city ofVolubilis in Morocco may have taken its name from theBerber namealili oroualilt for the flower.[14]
Nerium oleander is either native or naturalized to a broad area from northwest Africa through theMediterranean region and warmer areas of theBlack Sea region, Arabian Peninsula, southern Asia, and as far east asYunnan in southern parts of China.[15][16][17][18] It typically occurs around stream beds in river valleys, where it can alternatively tolerate long seasons of drought and inundation from winter rains.N. oleander is planted in many subtropical and tropical areas of the world.[citation needed]
On the East Coast of the US, it grows as far north asVirginia Beach, while in California and Texas miles of oleander shrubs are planted onmedian strips.[19] There are estimated to be 25 million oleanders planted along highways and roadsides throughout the state of California.[20] Because of its durability, oleander was planted prolifically onGalveston Island in Texas after the disastrousHurricane of 1900. They are so prolific that Galveston is known as the 'Oleander City'; an annual oleander festival is hosted every spring.[21]Moody Gardens in Galveston hosts the propagation program for the International Oleander Society, which promotes the cultivation of oleanders. New varieties are hybridized and grown on the Moody Gardens grounds, encompassing every named variety.[22]
Beyond the traditional Mediterranean andsubtropical range of oleander, the plant can also be cultivated in mildoceanic climates with the appropriate precautions. It is grown without protection in warmer areas in Switzerland, southern and western Germany and southern England and can reach great sizes in London and to a lesser extent in Paris[23] due to theurban heat island effect.[24][25][26] This is also the case with North American cities in thePacific Northwest likePortland,[27]Seattle, andVancouver. Plants may suffer damage or die back in such marginal climates during severe winter cold but will rebound from the roots.[citation needed]
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 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 such as spiders and wasps.[28]
The flowers require insect visits to set seed, and seem to bepollinated 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.[29][30] Fears of honey contamination with toxic oleander nectar are therefore unsubstantiated.[citation needed]
A bacterial disease known asoleander leaf scorch (Xylella fastidiosa subspeciessandyi[31]) has become a serious threat to the shrub since it was first noticed inPalm Springs, California, in 1992.[32] The disease has since devastated hundreds of thousands of shrubs mainly inSouthern California, but also on a smaller scale inArizona,Nevada and Texas.[33][34] The culprit is a bacterium which isspread via insects (theglassy-winged sharpshooter primarily) which feed on the tissue of oleanders and spread the bacteria. This inhibits the circulation of water in the tissue of the plant, causing individual branches to die until the entire plant is consumed.
Symptoms of leaf scorch infection may be slow to manifest themselves, but it becomes evident when parts of otherwise healthy oleanders begin to yellow and wither, as if scorched by heat or fire. Die-back may cease during winter dormancy, but the disease flares up in summer heat while the shrub is actively growing, which allows the bacteria to spread through thexylem of the plant. As such it can be difficult to identify at first because gardeners may mistake the symptoms for those ofdrought stress or nutrient deficiency.[35]
Pruning out affected parts can slow the progression of the disease but not eliminate it.[32] This malaise can continue for several years until the plant completely dies—there is no known cure.[20] The best method for preventing further spread of the disease is to prune infected oleanders to the ground immediately after the infection is noticed.
The responsiblepathogen was identified as thesubspeciessandyi by Purcellet al., 1999.[31]
Nerium oleander has a history of cultivation going back millennia, especially amongst the great ancient civilizations of theMediterranean Basin. Some scholars believe it to be therhodon (rose), also called the 'Rose of Jericho', mentioned in apocryphal writings (Ecclesiasticus XXIV, 13)[36] dating back to between 450 and 180 BC.[37][38]
The ancient Greeks had several names for the plant, includingrhododaphne,nerion,rhododendron andrhodon.[37] Pliny confirmed that the Romans had noLatin word for the plant, but used the Greek terms instead.[39]Pedanius Dioscorides states in his 1st century AD pharmacopeiaDe Materia Medica that the Romans used the Greekrhododendron but also the LatinOleander andLaurorosa. The Egyptians apparently called itscinphe, the North Africansrhodedaphane, and theLucanians (a southern Italic people)icmane.[40]
Both Pliny and Dioscorides stated that oleander was an effective antidote to venomous snake bites if mixed withrue and drunk. However, both rue and oleander are poisonous themselves, and consuming them after a venomous snake bite can accelerate the rate of mortality and increase fatalities.
A 2014 article in the medical journalPerspectives in Biology and Medicine posited that oleander was the substance used to induce hallucinations in thePythia, the female priestess ofApollo, also known as the Oracle ofDelphi in Ancient Greece.[41] According to this theory, the symptoms of the Pythia's trances (enthusiasmos) correspond to either inhaling the smoke of or chewing small amounts of oleander leaves, often called by the generic termlaurel in Ancient Greece, which led to confusion with thebay laurel that ancient authors cite.
In his bookEnquiries into Plants of circa 300 BC,Theophrastus described (among plants that affect the mind) a shrub he calledonotheras, which modern editors render oleander: "the root ofonotheras [oleander] administered in wine", he alleges, has a beneficial effect on mood:
The root ofonotheras [oleander] administered in wine makes the temper gentler and more cheerful. The plant has a leaf like that of thealmond, but smaller, and the flower is red like a rose. The plant itself (which loves hilly country) forms a large bush; the root is red and large, and, if this is dried, it gives off a fragrance like wine.
In another mention, of "wild bay" (Daphne agria), Theophrastus appears to intend the same shrub.[42]
Oleander was a very popular ornamental shrub in Roman peristyle gardens; it is one of the flora most frequently depicted on murals inPompeii and elsewhere in Italy. These murals include the famous garden scene from the House of Livia atPrima Porta outside Rome, and those from the House of the Wedding of Alexander and the Marine Venus in Pompeii.[43]
Oleander is a vigorous grower in warm subtropical regions, where it is extensively used as anornamental plant in parks, along roadsides and in private gardens. It is most commonly grown in its natural shrub form, but can be trained into a small tree with a single trunk.[44] Hardy versions like white, red and pink oleander will tolerate occasional light frost down to −10 °C (14 °F),[18] though the leaves may be damaged. The toxicity of oleander renders it deer-resistant and its large size makes for a good windbreak – as such it is frequently planted as a hedge along property lines and in agricultural settings.
The plant is tolerant of poor soils, intense heat, salt spray, and sustained drought – although it will flower and grow more vigorously with regular water. Although it does not require pruning to thrive and bloom, oleander can become unruly with age and older branches tend to become gangly, with new growth emerging from the base. For this reason gardeners are advised to prune mature shrubs in the autumn to shape and induce lush new growth and flowering for the following spring.[34] Unless they wish to harvest the seeds, many gardeners choose to prune away the seedpods that form on spent flower clusters, which are a drain on energy.[34] Propagation can be made fromcuttings, where they can readily root after being placed in water or in rich organic potting material, likecompost.
In Mediterranean climates oleanders can be expected to bloom from April through October, with the heaviest bloom usually occurring between May and June.Free-flowering varieties like 'Petite Salmon' or 'Mont Blanc' require no period of rest and can flower continuously throughout the year if the weather remains warm.
In cold winter climates, oleander is a popular summer potted plant readily available at most nurseries. They require frequent heavy watering and fertilizing as compared to being planted in the ground, but oleander is nonetheless an ideal flowering shrub for patios and other spaces with hot sunshine. During the winter they should be moved indoors, ideally into an unheated greenhouse or basement where they can be allowed to go dormant.[44] Once they are dormant they require little light and only occasional watering. Placing them in a space withcentral heating and poor air flow can make them susceptible to a variety of pests –aphids,mealybugs,oleander scale,whitefly andspider mites.[45]
Oleander flowers are showy, profuse, and often fragrant, which makes them very attractive in many contexts. Over 400 cultivars have been named, with several additional flower colors not found in wild plants having been selected, including yellow, peach andsalmon. Many cultivars, like 'Hawaii' or 'Turner's Carnival', are multi-colored, with brilliant striped corollas.[46] The solid whites, reds and a variety of pinks are the most common. Double flowered cultivars like 'Mrs. Isadore Dyer' (deep pink), 'Mathilde Ferrier' (yellow) or 'Mont Blanc' (white) are enjoyed for their large, rose-like blooms and strong fragrance. There is also avariegated form, 'Variegata', featuring leaves striped in yellow and white.[34] Several dwarf cultivars have also been developed, offering a more compact form and size for small spaces. These include 'Little Red', 'Petite White', 'Petite Pink' and 'Petite Salmon', which grow to about 8 feet (2.4 m) at maturity.[47]
Oleander is apoisonous plant because of toxic compounds it contains, especially when consumed in large amounts. Among these compounds areoleandrin and oleandrigenin, known ascardiac glycosides, which are known to have a narrowtherapeutic index and are toxic when ingested. Side effects after ingestion are weakness,diarrhoea,nausea,vomiting,headache, stomach pain, and death.[48]
Toxicity studies of animals concluded that birds and rodents were observed to be relatively insensitive to the administered oleander cardiac glycosides.[49] Other mammals, however, such as dogs and humans, are relatively sensitive to the effects of cardiac glycosides and the clinical manifestations of "glycoside intoxication".[49][50][51]
It is also hazardous to animals such assheep,horses,cattle, and other grazing animals,[52] with as little as 100 g being enough to kill an adult horse.[53] Plant clippings are especially dangerous to horses, as they are sweet. In July 2009, several horses were poisoned in this manner from the leaves of the plant.[54] Symptoms of a poisoned horse include severe diarrhea and abnormal heartbeat. This is aptly reflected in the plant'sSanskrit nameaśvamāra (अश्वमार), a compound ofaśva "horse" andmāra "killing".
In reviewing oleander toxicity cases seen in-hospital, Lanford and Boor[55] concluded that, except for children who might be at greater risk, "the human mortality associated with oleander ingestion is generally very low, even in cases of moderate intentional consumption (suicide attempts)."[55] In 2000, a rare instance of death from oleander poisoning occurred when two toddlers adopted from an orphanage ate the leaves from a neighbor's shrub inEl Segundo, California.[56] Because oleander is extremely bitter, officials speculated that the toddlers had developed a condition caused by malnutrition,pica, which causes people to eat otherwise inedible material.[57]
Ingestion of this plant can affect the gastrointestinal system, the heart, and the central nervous system. The main effect of cardiotoxic glycosides is positiveinotropy. Glycosides bind to the sarcolemma transmembrane ATPase of cardiac muscle cells and compete with K+ ions, inactivating the enzyme. This results in an accumulation of Na+ and Ca2+ ions into the cardiac muscle cells, leading to stronger and faster heart contractions. Moreover, the increased amount of extracellular K+ ions may lead to lethal hyperkalemia. Therefore, clinical features of oleander poisoning are similar to digoxin toxicity and includenausea,diarrhea, and vomiting due to stimulation of the area postrema of the medulla oblongata, neuropsychic disorders, and pathological motor manifestations.[17] Cardiotoxic glycosides are also responsible for stimulating the vagus nerve (leading to sinus bradycardia) and the phrenic nerve (leading to hyperventilation), and lethal brady- and tachyarrhythmias, including asystole and ventricular fibrillation.[58] Oleander poisoning can also result in blurred vision, and vision disturbances, including halos appearing around objects.[59] Oleander sap can cause skin irritations, severe eye inflammation and irritation, and allergic reactions characterized by dermatitis.[60]
The severity of the intoxication can vary based on the quantity ingested and an individual's physiological response, as well as the time of symptom onset after oleander ingestion: they can rapidly occur after drinking teas prepared with oleander leaves or roots or develop more slowly due to the ingestion of unprepared plant parts.[61]
Poisoning and reactions to oleander plants are evident quickly, requiring immediate medical care in suspected or known poisonings of both humans and animals.[60] Induced vomiting andgastric lavage are protective measures to reduce absorption of the toxic compounds.Activated carbon may also be administered to help absorb any remaining toxins.[17] Further medical attention may be required depending on the severity of the poisoning and symptoms. Temporary cardiac pacing will be required in many cases (usually for a few days) until the toxin is excreted.[citation needed]
Digoxin immune fab is the best way to cure an oleander poisoning if inducing vomiting has no or minimal success, although it is usually used only for life-threatening conditions due to side effects.[62]
Drying of plant materials does not eliminate the toxins. There is a wide range of toxins and secondary compounds within oleander, and care should be taken around this plant due to its toxic nature. Different names for oleander are used around the world in different locations, so, when encountering a plant with this appearance, regardless of the name used for it, one should exercise great care and caution to avoid ingestion of any part of the plant, including its sap and dried leaves or twigs. The dried or fresh branches should not be used for spearing food, for preparing a cooking fire, or as a food skewer. Many of the oleander relatives, such as the desert rose (Adenium obesum) found in East Africa, have similar leaves and flowers and are equally toxic.[citation needed]
Drugs derived fromN. oleander have been investigated as a treatment for cancer, but have failed to demonstrate clinical utility.[63][64] According to theAmerican Cancer Society, the trials conducted so far have produced no evidence of benefit, while they did cause adverse side effects.[65]
In a research study done by Haralampos V. Harissis, he claims that the laurel thePythia is commonly depicted with is actually an oleander plant, and the poisonous plant and its subsequent hallucinations are the source of the oracle's mystical power and subsequent prophecies. Many of the symptoms that primary sources such asPlutarch andDemocritus report align with results of oleander poisoning. Harissis also provides evidence claiming that the word laurel may have been used to describe an oleander leaf.[66]
The toxicity of the plant makes it the center of anurban legend documented on several continents and over more than a century. Often told as a true and local event, typically an entire family, or in other tellings a group of scouts, succumbs after consuminghot dogs or other food roasted over a campfire using oleander sticks.[67] Some variants tell of this happening toNapoleon's orAlexander the Great's soldiers.[68]
There is an ancient account mentioned byPliny the Elder in hisNatural History,[39] who described a region inPontus in Turkey where the honey was poisoned from bees having pollinated poisonous flowers, with the honey left as a poisonous trap for an invading army.[69][70][71] The flowers have sometimes been mis-translated as oleander,[11] but oleander flowers are nectarless and therefore cannot transmit any toxins via nectar.[29] The actual flower referenced by Pliny was eitherAzalea orRhododendron, which is still used in Turkey to produce ahallucinogenic honey.[72]
Oleander is the official flower of the city ofHiroshima, having been the first to bloom following the atomic bombing of the city in 1945.[73]
Oleander was part of subject matter of paintings by famous artists including:
Gustav Klimt, who painted "Two Girls with an Oleander" between 1890 and 1892.[74]
Vincent van Gogh painted his famous "Oleanders" inArles in 1888. Van Gogh found the flowers "joyous" and "life-affirming" because of their inexhaustible blooms and vigour.[75]
Anglo-Dutch artistSir Lawrence Alma-Tadema incorporated oleanders into his classically inspired paintings, including "An Oleander" (1882), "Courtship", "Under the Roof of Blue Ionian Weather"[76] andA Roman Flower Market (1868).
"The Terrace at Méric (Oleanders)", an 1867 Impressionist painting byFrédéric Bazille.[77]
In the 17th century ADFarsi-language book theJahangirnama, the Mughal emperor Jahangir passes a stream overgrowing with oleanders along its banks. He orders the nobles in his train to adorn their turbans with oleander blossoms, creating a "field of flowers" on their heads.[79]
Steely Dan's 1973 song "My Old School" contains the line "Oleanders growing outside her door, soon they're gonna be in bloom up in Annandale" in the second verse. It has been theorized that this reference is either a metaphor for a harmful relationship, ormarijuana, which is the subcontext of the song.[80]
^In the past, scented plants were sometimes treated as the distinct speciesN. odorum, but the character is not constant and it is no longer regarded as a separate taxon.
^abcdKathleen Norris Brenzel (2007).Sunset Western Garden Book. p. 495.
^Laura Murphy (2007-09-27)."Oleanders under attack"(PDF). College of Agriculture and Life Sciences at the University of Arizona. Archived fromthe original(PDF) on 2021-12-05. Retrieved2017-05-14.
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