Hi welcome to Taiga Bonzai, in the next few articles we discuss a selection of tree and shrub species used in bonsai that have defence mechanisms. Some are relatively harmless, whilst other are potentially lethal.

Introduction – in the early days of bonsai horticulture tree varieties included varieties of Juniper Juniperus Sp – Spruce Picea Sp – Pine Pinus Sp – Larch Larix and Acer Sapindaceae. As these were endemic to the various regions of China and Japan.

As time progressed, more species were added including flower and fruiting varieties. For example, Wisteria Floribunda and Azalea genus Rhododendron, Plum, Cherry, Peach and Apricot genus Prunus.

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 with devastating results.

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.

All flora have developed ways to defend themselves. Via the production of toxins in their sap, leaves, fruit and seeds, to the emittance of gas, or extremely sharp toxic thorns which deter most from ravaging their foliage.

Today one can find many plant species that originate from other realms, many of which are now cultivated in the west. The list of trees and shrubs used in bonsai is quite extensive, we will describe some of the common and exotic in alphabetical order.

Acacia genus Acacia, of which there are approximately 160 species of trees and shrubs within the pea family Fabaceae, native to Africa and Australia. Those of the African savanna have an abundance of thorns for protection, but also use poison as a second line of defence.

When this species 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. Hence, they too inject poison into their leaves. This information can be found in Sir David Attenborough’s book ‘The Private Life of Plants’ published in 1994.

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. The poison damages red blood cells, diminishing their ability to carry oxygen. Death can occur from between 18 hours to 10 days.

Apple – Malus 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 Buckthorn – ‎Rhamnus frangula L., this tree or shrub found among hedgerows, along roadsides and in woodlands has a number of toxic chemicals. Of which, Emodin is the dominant one, found in the 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.

Birch – Betula 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. 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.

Box – Buxus sempervirens, a common species found in bonsai collections is one to handle with caution as it is poisonous to humans. The leaves produce the 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, is a large deciduous tree with 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.

Cotoneaster – Cotoneaster 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.

Citrus – Citrus 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 Fir – Pseudotsuga 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.    

Dogwood – Cornus 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. 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.

Elder – Sambucus racemosa, is cited as a poisonous plant because the bark contains calcium oxalate crystals and the leaves and unripe fruits and seeds produce 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.

Elm – Ulmus. 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.

In toxic bonsai part II we continue the discussion on these trees and shrubs species, ‘letter’ ‘F ‘onwards, until then, BW, Nik.