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This site uses botanical names. Click here for an A to Z common name to botanical name converter.

A to Z of Poisonous Plants

What is a 'Poisonous Plant'?

Almost any plant can be poisonous. The humble marigold, Calendula officinalis, is said to act as an insect repellent so eating huge amounts of it might be expected to be harmful. Indeed, though used extensively both as an herbal medicine and as a tasty addition to a salad, its consumption when pregnant is not recommended.

The selection is by no means complete nor rational. The intention of The Poison Garden website is not to provide an encyclopaedia.

In particular, it should be noted that the plants included are generally one species from the genus and that the poisonous properties described can usually be expected to be present in all species in that genus.

For the purposes of The Poison Garden website, the selection has been based on those plants which either have a proven harmful effect in the sort of quantities which might be consumed or which, through their history and folklore, contribute to our understanding of the human race’s long relationship with the plants which have hindered, or helped, our evolution. Since they are based, to a large extent, on the poison plants studied for the Alnwick Garden Poison Garden they, in most cases, are plants which can be grown in climates similar to that found in the north-east of England.

A Word on Plant Naming

The current system of plant naming is based on the work of the 18th century Swedish botanist Carl Linnaeus. Under this hierarchical system a plant is allocated to a 'family'. Families may include many thousands of plants such as Ranunculaceae, the buttercup family, or as few as two as in the case of Cannabaceae which has only Cannabis and Humulus in the next level which is the 'genus'.


The material in the A to Z section is drawn from many sources. As well as books about the medicinal uses of plants from the so called 'Ebers' papyrus of around 1500BC to 20th century writers, a great many internet sites have been consulted and checked and, of course, many of the 'incidents' referred to are the anecdotes of visitors to the Alnwick Garden Poison Garden.

Rather than create a separate section detailing the lives of the authors of the many 'Herbals', you will find boxes like this one on some of the plant pages giving brief details of the people and their publications.

Plants within a genus are allocated to a 'species', and a plant name may stop at the species. Thus Digitalis purperea, is a complete plant name. Within a species, however, there can be 'varieties' defining a further level down in the plant's characteristics. Thus, Digitalis purperea 'Alba' is a white variety of the Digitalis purperea.

In some cases, the property of a plant may be common to the family - all members of the Ranunculaceae family are poisonous to a greater or lesser extent. With others the genus may be more defining in terms of properties; Euphorbia and Ricinus are both from the family Euphorbiaceae but are very different in their effects. In some cases, the species is significant in practical effects if not chemical composition; Senecio jacobaea, Ragwort, is a deadly nuisance whereas Senecio vulgaris, the common Groundsel, though poisonous, is simply a nuisance.

At the variety level, differences are limited to strengths of constituents; there are varieties of Cannabis sativa which produce low levels of THC and others where the THC levels can be much higher.

For a fascinating story of the two thousand year development of our understanding of plants which led to the Linnaean system of plant classification see Anna Pavord’s ‘The Naming of Names’.

Plants do not always stay in the same place in the naming structure. As botanists learn more about plant structures, they redefine some plants. The Datura plants in the A to Z list should be called Brugmansia as they have been reclassified but, as most of the folklore is in the previous name, that is the name used here. The system of naming plants is not, therefore, static.

Indeed, there are botanists who now believe that developments in the study of genetics mean we should look at a completely new system of classification.

The Meaning of 'Latin' Names

The international standard for plant names is based on Latin. But it would not be recognised as his native language by an ancient Roman. Plant names have arisen throughout history and many of the current names are constructions from different languages. Greek is often found to be the root of a plant name and others are based on the names of individuals being 'Latinised'.

For that reason, it is important to talk about the botanical names of plants rather than the Latin names. I think people are put off learning the unique botanical names of plants because they baulk at the idea of learning 'Latin'.

It can be quite difficult to get back to the complete root of a name. Many sources simply give a 'circular' definition; 'Ilex' is Latin for 'holly' and 'holly' in Latin is 'Ilex'.

On each of the plant pages, I have attempted to give an explanation of the original root of the plant name. Some of these are speculative in the extreme but, I think, understanding how a plant got its name helps us to understand what our ancestors knew, or thought they knew, about the plant concerned.

Common Names

This website is organised around the Linnaean system of plant naming but it is recognised that many people will know these plants better by a common name.

There are, however, a number of problems with using common names. First, common names can mislead. You would think that the only difference between the white hellebore and the stinking hellebore would be that the first was white and the second stank. But the first is Veratrum album and the second is Helleborus foetidus; the plants come from two different genera.

Common names can also be applied to more than one plant particularly as there are no ‘rules’ governing their use. Ricinus communis is the castor oil plant but Fatsia japonica which should be called the false castor oil plant is often called the castor oil plant, especially by garden centres who are reluctant to label a plant as ‘false’.

To assist the finding of one of the plants on this site from its common names click here for a cross reference to the most common ‘common’ names.

And the third problem with common names is that there are simply too many of them. Catha edulis has at least fifty common names and the Arum maculatum is said to have over one hundred.

Capitalisation of Plant Names

There are a number of ways plant names are presented. The Poison Garden website follows the Royal Horticultural Society in capitalising genera, using lowercase for species, title case and single quotes for varieties and lowercase for common names unless these include a word normally capitalised. For example, Aconitum lycoctonum is known as yellow wolfsbane and Lamarck's wolfsbane.

For more information on plant naming you can visit the RHS website.