Hi welcome to Taiga Bonzai, we continue our discussion albeit alphabetically through the list of shrubs and trees that have defence attributes.

Introduction – some of these defensive toxins are harmful to domestic pets and also to humans. Consuming any part the of tree/shrub can cause severe ailments for example, Rhubarb in the family Polygonaceae.

The use of rhubarb stalks as food is a relatively recent innovation first recorded in 18th to 19th-century. However, the leaves of the plant are poisonous as they contain such substances including, oxalic acid, a nephrotoxin. Yet the stalks are widely used for making pies, tarts, crumbles and in wine production.

Oak – Quercus. family Fagaceae. A deciduous and evergreen tree with a variety of species that include, white oak Quercus alba and stone oak Lithocarpus. Oak leaves and acorns are poisonous as they contain tannic acid, which can cause kidney damage, gastroenteritis and diarrhoea in livestock for example.

Sheep, goats, horses and cattle, but it has little effect on the domestic pig. It is said humans are not affected providing the tannins have been removed nonetheless, those with sensitive digestion systems should avoid consumption.

Oleander – family Apocynaceae. A small tree or shrub having approximately 400 different varieties in the genus Nerium, can be found in many temperate zones throughout the world. It is widely cultivated as an ornamental plant for parks and gardens reaching heights of 2 to 6.5m. (19ft) Although there now exist many dwarf varieties, which only grow to 26cm (10 ins) and these can be found in some bonsai collections.

Oleander when mature has grey bark, with dark green thick leaves arranged in pairs that are relatively narrow in shape. The flowers from white to pink to red are highly scented although much depends on the variety and fruit in a long pod.

These when ripe open to reveal large amounts of seed. Oleander although a very attractive plant, is considered extremely poisonous as it contains the toxins oleandrin and oleanrigenin that are referred to as cardiac glycosides.

Ingesting any part of an Oleander can cause serious gastrointestinal problems; nausea, vomiting, excess salivation, abdominal pain and diarrhoea. Other reactions to Oleander glycosides include cardiac and central nervous system effects. An irregular or erratic heart rate and drowsiness, muscle tremors, seizures and collapse that can have fatal consequences.

Olive – Olea europaea. family Oleaceae. Olive trees are not toxic and ingesting the fruit has no known side effects. However, olive tree pollen is extremely allergenic and according to the Ogren Plant Allergy Scale. A rating system for plants measuring their potential to cause allergic reactions in humans, it has a rating of 10 out of 10. As the olive tree is wind-pollinated and the pollen if inhaled, can cause headache, blocked sinuses, breathing difficulties and serious asthma attacks.

Orange jasmine – Murraya paniculata. family Rutaceae. A tropical evergreen tree or shrub from Asia is a common specimen for bonsai. It has glossy leaves and white scented fragrant flowers that can remain throughout the growing season and fruit ranging from orange to red, resembling the kumquat.

The orange jasmine has no known toxins harmful to humans, but the flowers are highly allergenic and can cause headache, blocked sinuses and breathing difficulties and in some instances severe asthma.

Plum – Prunus Spp. family Rosaceae. Is a diverse group having many species between 19 and 40 according to taxonomists. Arguably the most common plum trees used in bonsai are the European plum Prunus domestica and the Japanese plum Prunus salicina. The flowers are fragrant and vary from white to cream, to various shades of pink.

The fruits are usually globose to oval between 2cm to 6cm in size with firm flesh surrounding a hard seed pod. Plum seeds contain the toxin cyanogenic glycosides including amygdalin that decompose into a sugar molecule. Resulting in the production of Hydrogen cyanide gas, which is extremely poisonous and flammable.

Podocarpus – Podocarpus neriifolius. family Podocarpaceae. There are approximately 97 to 107 species in the genus that are related to conifers and can be found in bonsai collections. Podocarpus are evergreen with cones forming a brightly coloured fleshy, berry-like receptacles inviting birds to feed and in so doing the seeds are dispersed through their digestive tracts.

Podocarpus are also related to yews, thus their leaves, stems, bark and pollen are cytoxic. In spring and early summer, the male Podocarpus blooms and releases the cytotoxic pollen. Exposure to this can create an effect mimicking the cytotoxic side effects of chemotherapy, where blood cells or bone marrow are most at risk of developing serious infections.

Privet­ – Ligustrum vulgare, family Oleaceae. A species native to Europe, Australia, Africa and Asia is commonly used in bonsai. Species include the Japanese privet Ligustrum japonicum, Chinese privet Ligustrum quihoui, which are mainly used for ornamental plants and Ligustrum ovalfolium for hedging purposes.

The latter if managed regularly is quite decorative, but if left to its own devices will become unruly. Privet leaves and bark have bitter properties, which in China are used for making herbal teas. However, privet species that yield fruit should not be ingested as they are toxic. Symptoms include nausea, headache, abdominal pains, vomiting, diarrhoea, low blood pressure and weakness.

Quince – Cydonia oblonga family Rosaceae. Include such species as Chaenomeles japonica and Pseudocydonia sinensis that are small deciduous fruit and flowering trees. The flowers borne in clusters vary according to the species from pale pink to red and both species bear fruit in the form of a pome.

This pome is bright golden-yellow at maturity and although the fruit is edible, it is astringent and can cause a shrinking or constriction of the body tissues for example. A dry puckering of the mouth due to the tannins present. The quince has been used for both culinary and medicinal purposes. But it is poisonous as the seeds contain nitriles, that if ingested will be hydrolysed by the stomach acid producing hydrogen cyanide.

It is strange to think that many plants used for both medical and culinary purpose are quite toxic. Yet if they are prepared correctly they are made safe to consume. In the next article on this subject we continue the discussion beginning with the letter ‘R’ onwards, until next time, BW, Nik.