Article 23 – ‘Toxic Bonsai II’

Toxic Bonsai Part II

Ginkgo biloba – Family Ginkgoaceae. Also known as the maidenhair tree native to China is the only living species in the division Ginkgophyta, as all others are now extinct. Its fruit is used for culinary purposes and in traditional Chinese medicine and is considered by some to contain aphrodisiac properties. However, the seed pulp has toxins that are not destroyed when cooked and if eaten in large amounts poisoning by methyl pyridoxine, (neurotoxin) can cause epileptic seizures. In addition, the sarcotesta or fleshy seed coat is poisonous and disposable gloves are required as they are able to cause dermatitis and or blisters. Other side effects include; nausea, vomiting and diarrhoea.

Guelder roseViburnum opulus. A deciduous shrub can be found in woods, hedges and in areas containing a lime-rich soil compound. The tree has large white flowers with smaller yellow ones on the inner part of the cluster, the white flowers are infertile whilst the yellow ones are fertile. In autumn the flowers produces red berries with a single seed in each. All parts of the tree are poisonous to humans as they carry toxins such as iridoid glycoside, isobutyric Acid, coumarins, tannins and saponins. These can cause severe nausea, vomiting, diarrhoea, swelling and over heating.

Grevillea robusta – Family Proteaceae. Commonly known as the Australian silver oak although uncommon can be found in European bonsai collections. This evergreen tree with its feather like leaves similar to a fern frond is known for its prolific growth and produces golden orange blooms. The flowers and fruit of G. robusta are poisonous, they contain hydrogen cyanide sometimes referred to as Prussic acid and tridecylresorcinol responsible for severe contact dermatitis.

Honey LocustGleditsia triacanthos. Is not a toxic tree unlike its ‘look-alike’ counterpart the black locust, Robina pseudo which is extremely poisonous. The two species can be identified as follows: the black locust has wisteria like flowers and small black seed pods, whilst the honey locust has small clusters of flowers and long seed pods 15–20 cm. Honey locust trees have extremely sharp thorns 3 cm to over 20 cm protruding from the branches, that harden and turn red as they age, then fade to grey becoming brittle as they mature. As a result the honey locust is considered difficult to wire and shape although thorn less varieties (Gleditsia triacanthos var. inermis) are occasionally found growing wild and are available as nursery plants. But there is no guarantee they are free from toxins.

HollyIlex. Family Aquifoliaceae. There are 400 to 600 species ranging from evergreen to deciduous trees and shrubs, found in temperate to tropical climates around the world with many shaped into bonsai. The bark is relatively smooth with small nodules known as ‘warts’, the glossy oval leaves are dark green in colour. Holly is dioecious meaning that the flowers of male and female are peculiar to their own sex and tree. These flowers 4 white petals when mature become scarlet berries and are attractive to birds, whom ingest them, but pass the seed through their digestive system intact. However, for humans they are predominantly poisonous as is the rest of the tree. Holly contains such toxins as caffeic, feruloylquinic, chlorogenic and quinic acids, kaempferol, tannins, rutin and theobromine compounds found in all parts of the plant. Holly berries can cause severe vomiting, diarrhoea and nausea that can be fatal for young children if consumed.

HawthornCrataegus. Family Rosaceae. Is a species quite common in bonsai grown for its floral display. The flowers are hermaphrodite, meaning both male and female reproductive parts are contained within each flower. Flowers are highly scented, white or occasionally pink with five petals, and grow in flat-topped clusters, with small pome fruits and thorny branches. Although hawthorn fruit is not toxic if used in herbal remedies and culinary purposes it must be prepared properly. Failure to do so can cause nausea and sedation, cardiac arrhythmia and dangerously low blood pressure if taken in large quantities. Those taking digoxin a medication used to treat various heart problems should avoid hawthorn completely.

Indian PeaLathyrus sativus. Family Fabaceae. Although not really considered as bonsai material, is often cultivated for its striking blue flowers, but more importantly as an insurance against famine in third world countries where drought is a major problem. The crop is harmless to humans if ingested in small quantities occasionally, but continuous intake over a prolonged period (3 months) can have serious side effects. The plant produces seeds containing diaminopropionic and neurotixic amino acids and can cause a disorder known as lathyrism. A neurodegenerative disorder causing paralysis of the lower body, emaciation of gluteal muscle and brain damage in children.

Idesia – Family Salicaceae. A tree not normally found in western bonsai collections is common in its native regions of China, Japan, Korea and Taiwan. It is a deciduous tree with greyish-green bark and heart shaped dark green leaves 8 to 20cm in length protruding from a red petiole. Flowers are small, fragrant and yellowish green in colour. The fruit of the Idesia is a small orange berry, which ripens to dark red almost purple in colour, that can be consumed, but as with all wild fruit care should taken in its preparation prior to ingestion. Idesia has no known toxins that are harmful to humans.

Incensed Cedar – Libocedrus decurrens. Family Cupressaceae. Is a popular species for bonsai as formal, informal and literati styles. It contains strong volatile oils including thujone, a ketone that is known to be toxic in large quantities and it is best known as a chemical compound in the spirit absinthe. Thujone has a menthol odour and is considered toxic to the brain, kidney, and liver cells and could cause convulsions if used in too high a dose. It should not be used during pregnancy, breastfeeding or those with kidney weakness.

JacarandaJacaranda mimosifolia, Family Bignoniaceae. Has been cultivated in many temperate parts of the world and also in bonsai thriving in sandy soils with full sunlight. Young trees are unable to withstand cold conditions, but mature specimens are able to tolerate temperatures down to -7°C (19°F) for brief spells. The jacaranda is known for its stunning display of flowers produced in large panicles, with colours ranging from blue to purple and fruit in a flattened oblong pod containing the seeds. Nonetheless, the Jacaranda is said to be toxic, exposure to the pollen can cause skin irritation and rash. Ingesting either and or flowers and seeds can result in, vomiting, nausea and abdominal pain.

Jade treeCrassula ovata. Family Crassulaceae. Has other common names including, ‘Friendship tree’, ‘Money tree’ and ‘Lucky plant’ and is native to south Africa and Mozambique and is found throughout the world as a common house plant. Arguably, C. ovata is not a true tree in the sense of the word, meaning it does not shed its leaves or needles on an annual basis as deciduous and conifers do. It is a succulent, a water retaining plant that has the ability to thrive on limited water sources. Whereas most conifers and deciduous trees require a constant supply of water that is continuously pumped through its system. In addition, its trunk and branches never become true lignified tissue, they remain soft and fleshy during the plants life. Nonetheless, it is found in many bonsai collections with some attractive results. C. Ovata has rich jade green thick, shiny, smooth, leaves growing in opposite pairs along the branches. Some varieties may have a yellowish-green appearance, whilst others have a red tinge on the edges. The flowers of C. Ovata under the right conditions are small star-like white or pink flowers arriving in early spring. The jade plant is poisonous to domestic pets (dogs and cats) and marginally toxic to humans and if ingested may cause vomiting, diarrhoea, abdominal discomfort, loss of appetite and lethargy.

JasmineGelsemium sempervirens. Family Gelsemiaceae. A relatively common species found in bonsai collections for its individual trumpet shaped yellow flowers, that are strongly scented and appear on the tree prior to the production of new growth. However, all parts of this species are poisonous containing toxins such as strychnine related alkaloids and gelsemine a highly toxic compound that acts as a paralytic and often results in death. In addition, the sap from this plant can cause severe problems if in contact with those having sensitive skin causing rash and swelling.

JuniperSpp. Family Cupressaceae. This order has many species widely used in bonsai horticulture and it is argued that they are all toxic due to the volatile oils found within the plant. Alpha-pinene, myrcene and sabinene, which if ingested can cause diarrhoea, nausea and hypertension. Although considered by many to be safe for culinary uses, juniper berries if consumed on a regular basis can cause cause serious kidney damage. Pregnant or breastfeeding women are advised to refrain from usage due to the risk of miscarriage. Those taking Telmisartan a prescribe drug, which is used to treat high blood pressure (hypertension) should refrain from ingesting any part of this plant.

Kentucky coffeeGymnocladus dioicus. Family Fabaceae. A species native to north America is also used in bonsai. Its rough ash-grey bark similar to that of oak can fall or peel away from its surface leaving scarring and indentations, which adds character to the tree. Its flowers are dioecious and has fruit in the form of a hard-shelled bean in pods from 13cm to 25cm. (5 to 10 inches) The seeds are considered poisonous as they contain the toxic alkaloid cytosine, that if consumed can cause respiratory difficulties, which can have fatal results. However, it is argued that if the seeds are roasted, the cytosine is neutralized, but for those with respiration problems it is not a risk worth taking.

KumquatFortunella japonica. Family Rutaceae. The species has no known toxins harmful to humans and is usually grown as an ornamental plant, but is found in bonsai collections. The fruit resembles a small orange a little larger than a grape, its peel has a sweet flavour whilst the inner pulp is sour but is edible when cooked. It is also ingested in its raw state, but those with a sensitive digestion system should refrain from doing so due to the concentration of oils (Limonene) and acids within the fruit. Which can cause diarrhoea, nausea and other abdominal complaints.

KurrajongBrachychiton populneus. Family Malvaceae. Is native to Australia and found in various habitats from wet coastal districts to semi-arid regions. The bell-shaped flowers range in colour from pale cream to pink with simple pointed shaped leaves. The seeds are covered in small stiff irritating hairs, which have to be removed prior to roasting and ingesting as they contain toxins. Although these are not considered dangerous to humans they can be to domestic pets, sheep and cattle causing lameness, tremors, collapse and in some cases fatality depending on the victims disposition.

Laburnum – Family Fabaceae. Is a genus of two species of trees that are Laburnum anagyroides known as the common laburnum and Laburnum alpinum the alpine laburnum. They are often found in bonsai collections due to their colourful yellow pea-like flowers. That are in pendulous leafless racemes 10–40 cm (4–15.5 in) similar to the wisteria, making them very popular trees. However, all parts of the tree are poisonous; roots, bark, wood, leaves, flower-buds, petals and seeds as they contain the toxin cytosine a nicotinic receptor agonist that produces a biological response. Symptoms may include intense lethargy, vomiting, convulsion, coma and severe diarrhoea.

Laurel (Cherry) Prunus laurocerasus. Family Rosaceae. Is a shrub often used for topiary in hedging and also in bonsai as it is easily shaped. The leaves are a shiny dark green with creamy white flowers and fruit that turn black when ripe. The whole plant is poisonous containing the toxin hydrogen cyanide, also known as prussic acid and identifiable by its strong almond-like smell and bitter taste. Symptoms can include breathlessness, weakness, spasms, convulsions, coma and respiratory failure.

ManchineelHippomane mancinella. Family Euphorbiaceae. Classed as an endangered species is a flowering and fruiting tree native to Florida, Mexico and the Bahamas growing among mangroves and in coastal waters. Its fruits are green and round resembling a small apple, hence its common name the ‘Beach apple’. H. mancinella is an evergreen tree with reddish-grey bark, glossy oval green leaves, greenish-yellow flowers and grows to a height of approximately 15m. (49ft) It is also known in Spanish as ‘Manzanilla de la muerte‘, the ‘Apple of death’ and is considered one of the most dangerous trees in the world. All parts of the tree are extremely poisonous with arguably the sap being the most toxic as it contains phorbol a member of the tiglian family of diterpenes. Even the smallest amount diluted in water can cause severe blistering of the skin and ingesting the fruit can cause intense gastrointestinal problems that can have fatal results. Manchineel is cultivated for its timber source, but little is known of its use in bonsai.

MistletoeViscum album. A hemiparasitic plant in the order Santalales. A mistletoe seed attaches itself to a tree by a structure called the haustorium and is able to germinate independently, but as it develops it penetrates the branch of its host absorbing nutrients and water. The European mistletoe has evergreen leaves in pairs with waxy white berries in clusters of two to six, that contain the toxins polysaccharides, alkaloids, and lectins. Which can cause blurred vision, nausea, abdominal pain, diarrhoea, blood pressure changes that can be fatal. Those taking Telmisartan a prescribe drug, which is used to treat high blood pressure (hypertension) should be aware of potential problems. Mistletoe is found in bonsai, but is uncommon as it can affect other species within a collection.

Mock orangePhiladelphus coronarius. Family Hydrangaceae. A species of flowering plant native to Southern Europe is a deciduous shrub growing to approximately 3 m tall by 2.5 m wide and often found in bonsai collections. What makes this a popular collectable species is because of its bowl-shaped double white flowers on prominent stamens, that are highly fragrant. The ‘toothed’ dark green leaves turn to yellow in autumn adding more colour to the plant. Yet the seeds and flowers carry toxins that although considered mild and not life threatening, can cause nausea, vomiting, diarrhoea and skin rash if consumed. But much will depend on an individual’s digestive system.

MyrtleMyrtus communis. Family Rosopsida. A common species found in bonsai has reddish brown bark that is apt to peel off in mature plants. The flowers usually white in colour have five petals and numerous long stamina and can be heavily scented. The leaves are small, narrow and dark-green and filled with oil, which is visible as small dots when held against a light. This oil is slightly toxic and may cause headaches, nausea, indigestion, and may colour urine purple if consumed in large quantities.

In toxic bonsai part III we continue the discussion on species ‘N’ to ‘T’ until then BW, N.

Article 22 – ‘Toxic Bonsai I’

Toxic Bonsai (Part I)

In the early days of bonsai horticulture tree varieties included the Juniper JuniperusSpruce Picea Pine Pinus and Larch Larix. As time progressed, more species were added for example, flower and fruiting varieties Wisteria Floribunda and Azalea genus Rhododendron, in the genus Prunus plum, cherry, peach and apricot. Today many other species from around the globe have now become part of bonsai horticulture including those which may be considered as common, the European Horse Chestnut Aesculus hippocastanum the unusual Acacia genus Acacia and the exotic, the Madagascar Euphorbia milii described below.

Many bonsai enthusiasts either have traditional collections predominantly coniferous, whilst others prefer deciduous and some will have an assortment of species. These artistically shaped miniature trees portray delicate, graceful and rugged forms and although their beauty is beholding, all is not what it seems. These little adaptations are able to produce toxins just as their full-sized counter parts can, which have the power to incapacitate all fauna including humans even to the point of being lethal.

All flora have developed ways to defend themselves, from the production of toxins in their leaves, fruit and seeds to the emittance of gas and or extremely sharp thorns which deter most from ravaging their foliage. The European Horse Chestnut Aesculus hippocastanum a large deciduous tree has greenish-yellow to white flowers and fruit contained in spiny capsules. In the UK at autumn time children collect the fruit capsules and remove the seeds from within, thread them on lengths of string and participate in an old traditional game of ‘Conkers’. A game dating back to 1848 where turns are taken in striking each others ‘conker’ until one breaks; yet the players who take part in this ritual, are probably unaware that these ‘conkers’ or seeds are poisonous.


Acacia genus Acacia, of which there are approximately 160 species of trees and shrubs within the pea family Fabaceae are native to Africa and Australia. Those of the African savanna have an abundance of thorns for protection, but also use poison in their leaves as a second line of defence. When the tree is disturbed it pumps poison into its leaves releasing ethylene gas from the pores. This gas release if detected by other acacias in near proximity sound the alarm alerting them to a potential threat and in so doing they too inject poison into their leaves.


The Madagascar Euphorbia milii commonly known as the Crown-of-thorns – a shrub with flower clusters and red, petal-like bracts has thorns that are poisonous. These thorns if damaged secrete a latex sap called urushiol and when in contact either on or under the skin can cause a sumac rash a very serious allergic reaction; a form of dermatitis.


Perhaps the question on most peoples lips is why would you want to have a tree that is poisonous? The question can be answered in two ways (a) why do people keep exotic pets, arachnids such as the Mouse Spider Missulena, which is every bit as dangerous as it looks or a Burmese python Python bivittatus that can be extremely aggressive. Pterois, or lion fish with its showy pectoral fins and venomous spiky fin rays, a popular choice among marine aquarists. It is really down to human nature, some are content to have the mundane household ‘moggy’ (cat) as a pet, whilst others want something which can be seen as diverse. (b) It is possible that somebody was given a bonsai as a gift without the purchaser bothering to research the tree’s attributes, it just looked nice. Furthermore, most bonsai contain toxins of one sort or another in their defence that vary in type and amount.

There are countless species of flora that exist on the planet including wild or natural varieties and hybrids, the latter pioneered by Gregor Mendel whom is credited with starting the hybrid plant revolution with his genetic studies of peas in the early 1900s. And least we forget those that have been genetically modified to produce more flower and fruit and combat insect infestation. To describe the peculiarities and properties of flora is a monumental task and narrowing it down specifically to bonsai, would amount to a PhD thesis. Therefore, the discussion will be further refined focussing on bonsai that can be found in most collections either common or unusual. The complete topic will be in four parts this post being part I and arguably the most efficient way in undertaking this, is to list them in alphabetical order.

Acer – Family: Aceraceae. The toxins are found within the leaves which increase as they wilt and die. It is also found in the seeds although the content is less. The acer although not harmful to domestic pets and humans is potentially fatal to equines if ingested as the poison damages red blood cells, diminishing their ability to carry oxygen. Death can occur from between 18 hours to 10 days.

AppleMalus Spp. The seeds are mildly poisonous and contain a small amount of amygdalin a cyanogenic glycoside that play important roles in many plants including apple varieties. However, the amount of cyanogenic glycoside contained within the seed is not considered dangerous to humans nonetheless, ingesting a large quantity can provide severe side effects.

Alder BuckthornRhamnus frangula L. This tree or shrub found among hedgerows, along roadsides and in woodlands, has a number of toxic chemicals, including emodin that are within its bark and purple-black berries or fruits. Emodin is a purgative resin, which is also found in rhubarb and also produced by many species of fungi. If ingested the symptoms are: collapse, convulsions, diarrhoea, gastroenteritis, haemorrhage and vomiting.

Azalea – genus Rhododendron Family Ericaceae. Is a common species that appear in bonsai collections but, it is poisonous. The toxins Grayanotoxin and arbutin glucoside are found in all parts of the plant the flowers, leaves and nectar – the latter often referred to as ‘mad honey’. They can cause nausea, vomiting, weakness, dizziness, breathing difficulties, low blood pressure, reduced heart rate and irregular rhythm, which could be life threatening.

Beech – genus Fagaceae. Indigenous to Europe, Asia, and North America produce a triangular shaped fruit called beechnuts in the autumn. These nuts often used as a food source are high in tannins having a strong bitter taste and are toxic to both canines and humans especially children if consumed in large quantities. The European beech Fagus sylvatica, is believed to be more toxic than its the American relative, Fagus grandifolia. Symptoms include; vomiting, diarrhoea, abdominal pain, nausea, fatigue and dilated pupils – mydriasis.

BirchBetula Spp. Has more homeopathic properties as opposed to toxins nevertheless, pollen from the silver birch, Betula pendula, is the second most severe allergen for people as it can travel many kilometres via the wind. It is able to cause hay fever, conjunctivitis and severe respiratory problems with disease to the lungs and asthma. Severe cases of pollen infection do require medical attention.

BoxBuxus sempervirens. A common species found in bonsai collections is one to handle with caution as it is poisonous to humans. The leaves produce an alkaloid buxine which causes nausea, vomiting and diarrhoea and respiratory paralysis in humans and livestock. Contact with skin can cause irritable rashes and when pruning the clippings should be handled with care.

Cherry (Wild) – Prunus Spp. Wild Cherry trees produce fruit that are reddish black in the summer, which can be consumed. However, the wild cherry twigs and leaves contain the chemical prunasin, a cyanide that when ingested, can be fatal. Prunasin breakdown and cyanide release occurs when the tree becomes stressed and an indication of this is when the leaves begin to wilt.

Chestnut (European horse) – Aesculus hippocastanum. As described above.

CotoneasterCotoneaster Spp. Are grown as bonsai mainly for their display of coloured berries ranging from bright orange to red to purple. This species is said to be a high risk in the toxicity range, because their leaves, berries and flowers all contain cyanogenic glycosides. These toxins if ingested are converted to cyanide during digestion causing serious effect on the heart, liver, kidney and brain. For children the risk is higher than in adults, although much depends on the amount consumed.

CitrusCitrus Spp. Citrus oil is a concentrate of the fruit produced by the tree and also a protective barrier found on the leaves, which can be activated by a gentle rubbing with the fingers. The scent of the oil is pleasant but the taste is bitter, leaving a nasty after taste due to Coumarin a fragrant organic chemical compound in the benzopyrone class. Although citrus oil is not harmful to humans, felines are more susceptible to citrus poisoning, which can result in diarrhoea, vomiting, liver damage or even death.

Douglas FirPseudotsuga menziesii. A native of north America has smooth grey bark when young that are covered with numerous resin blisters, which should not be ingested. The leaves needle like in appearance have two whitish stomatal bands on their underside, that are pores to allow the exchange of gas. If the leaves are damaged they emit a sweet fruity-resinous scent. Ingesting needles can result in vomiting, anorexia, abdominal pain, and lethargy. Other trees with similar attributes are: the Balsam Fir Abies balsamea, Blue Spruce Picea pungens, Red Spruce Picea rubens, White Spruce Picea glauca, Scots Pine Pinus sylvestris and Red Pine Pinus resinosa.    

DogwoodCornus Spp. A genus comprising of approximately 60 different varieties known for their brilliant floral displays in spring time. The fruits of many dogwood varieties are rather tart and unpalatable due to the amount of Tannins, but can be consumed if cooked. However, fruit of the dogwood in the sub-genus Swida are toxic and should be avoided. Dogwoods are prone to attack by insects and fungal disease for example. Botryosphaeria Canker a dark yellowish pitch that oozes from dogwoods and Phytophthora a reddish orange sap oozing from the tree as a result of destroyed tissue. Dogwoods infected with this disease should be kept away from pets, children and other plants.

Dieffenbachia – Family Araceae. A native from Mexico, West Indies and Argentina is widely cultivated as an ornamental houseplant and although not considered by some traditionalists as bonsai material, it is found in some collections. Dieffenbachia is poisonous, it contains Raphides needle-shaped crystals of calcium oxalate crystals and if the leaf or its residue is ingested it causes a burning sensation and erythema a redness of the skin or mucous membranes, caused by increased blood flow. Dieffenbachia can cause other symptoms including numbness, oral irritation and localized swelling.

ElderSambucus racemosa. Elder is cited as a poisonous plant because the bark contains calcium oxalate crystals and the leaves and unripe fruits and seeds cyanoglycoside sambunigrin. But, ripened fruit when subjected to a cooking process reduces the toxins. Elder suffers from Hyphodontia sambuci or Elder Whitewash a basidiomycete fungal pathogen forming a thin white, pruinose (flour-like dusting) on the limbs and branches. The pathogen should be avoided as the spores are easily carried by a gentle breeze.

ElmUlmus. The elm has no toxins to speak of that are a danger to humans or domestic pets but its seeds, leaves and bark should not be ingested as a precaution. Because it is possible that the tree may be infected by Ascomycetes a pathogen relatively common to this species. Ascomycetes not only infest and destroy, they also produce secondary metabolites that are poisonous.

Eucalyptus – Family Myrtaceae. The leaves of this tree contain an oil that if treated and diluted can be safe for adult humans. But untreated oil is extremely toxic and ingesting a small amount (3.5 mL) can have fatal results. Symptoms of eucalyptus poisoning may include stomach pain, a burning sensation, dizziness, muscle weakness, small eye pupils, suffocation, nausea, vomiting, and diarrhoea.

Ficus – Family Moraceae. Is a genus of approximately 850 species that include trees, shrubs and vines collectively known as fig trees. Common species used in bonsai Ficus microcarpa and Ficus benjamina are quite popular especially as a beginners tree. However, they are poisonous due to the milky white sap containing Furocoumarins psoralens and ficin that oozes out when pruned. This sap causes Dermatitis and allergic reactions for example, itching of eyes, coughing and wheezing, skin irritation with redness and stinging.

Forsythia – Family Oleaceae (olive family) is also a popular choice in bonsai and there are eleven species predominately native to Asia. The species Forsythia suspensa is considered a major herb used in Chinese medicinal practices as it is non-toxic. But for safety reasons, one should not consume any part of the plant that is not edible.

Firethorn Family Rosaceae. A large shrub with sharp thorns related to the Cotoneaster (Cotoneaster is thornless). This a popular choice for bonsai due to its bright red and orange fruit that are toxic. The seeds of the berries contain cyanogenic glycosides as do almonds, apples, cherries and plums that can cause gastro-intestinal problems when ingested raw. They are only edible if crushed and washed under running water.

In toxic bonsai part II we continue the discussion on species ‘G’ to ‘M’ until then BW, N.