Poison in the garden


The gates of Alnwick Poison Garden, north-east England. Image by Jacqui (CC BY-NC-ND 2.0) via Flickr

While giving my undergraduate class a tour of a botanic garden, a university professor said that “we should only eat the parts of a plant that the plant wants us to eat”. He was referring to the fruit, which many plants encourage animals to eat in order to spread their seeds in the environment (though not all fruits are edible). I don’t think he meant us to take his advice literally, but it is sensible to eat plants with caution. Alongside famous poisons including belladonna and hemlock, plants produce a variety of other molecules that aim to deter animals from eating them. Some of these molecules – such as ricin, which is produced by the castor oil plant – are so poisonous that tiny quantities can kill you. Others, like caffeine or the anti-malaria drug quinine, have less dramatic effects on the human body that we may find desirable or useful.

I recently visited The Alnwick Garden in north-east England, which has a special garden dedicated to educating visitors about the potential dangers of plants. In fact, some of the plants on display in the Poison Garden are so dangerous that visitors can only enter as part of a guided tour. I really enjoyed the tour and if you are ever in the area I recommend you pay the garden a visit.

The tour included some well-known poisonous plants, but the main message I took home from the tour was that many common garden plants are also potentially dangerous if they touch your skin or you accidently eat them. Below are a few examples of common plants that aren’t as benign as they might first seem:

Rhubarb (Rheum x hybridium)

While the pink fleshy stalks of the rhubarb plant are safe to eat and are commonly used in desserts, the leaves are highly toxic (1). This is thought to be due to the presence of high levels of oxalic acid, which can interfere with chemical reactions in the body by combining with calcium and other metals.

Common ivy (Hedera helix)

This rapidly growing vine is a haven for wildlife and attracts at least 70 species of nectar-feeding insects in its native range of Europe and Western Asia (2). Contact with ivy can cause an allergic skin reaction in some people, due to a natural pesticide in the leaves called falcarinol (3). Regardless of whether you are allergic to ivy or not, you should avoid eating this plant because its leaves contain saponins, which can cause vomiting, convulsions and even death.

Common nettle (Urtica dioica)

Children quickly learn that contact with common nettles results in a painful stinging sensation and skin inflammation. This is due to a cocktail of molecules including histamine, serotonin and oxalic acid, which is released from hairs on the surface of the leaves. For more information check out this cool infographic by Compound Interest.

Common laburnum (Laburnum anagyroides)

All parts of this small tree are poisonous, due to the presence of a molecule called cytisine, which has a similar structure to nicotine and has similar effects on the body. Laburnam is a member of the pea family and cases of laburnam poisoning are often caused by individuals mistaking laburnum seeds for peas and eating them (4). Mild cases may cause nausea and vomiting, but laburnum poisoning can also lead to insomnia, convulsions and coma.

These are just a few examples of common garden plants that can be harmful to humans and other animals. Fortunately, you can protect yourself against these and other poisonous plants by taking simple precautions, such as wearing gloves while gardening and carefully identifying edible plants when foraging.

Author’s note: Sorry for the long silence on this blog. My life has been quite chaotic in the last few months due to several events (expected/not expected, good/bad) and so the blog has had to take a back seat. Things are calming down a bit now so I’m hoping to get back into posting regularly, probably about twice a month. As ever, I’m always keen to receive guest posts so if you are interested in writing for Plant Scientist, please do get in touch.


  1. The Poison Garden blog: Rheum x hybridium http://www.thepoisongarden.co.uk/atoz/rheum_x_hybridum.htm
  2. Wikipedia: Hedora helix https://en.wikipedia.org/wiki/Hedera_helix
  3. Compound interest advent calendar http://www.compoundchem.com/2014advent2/
  4. The Poison Garden blog: Laburnam anagyroides http://www.thepoisongarden.co.uk/atoz/laburnum_anagyroides.htm

The plant scientist and novice gardener


My mini herb garden. From left to right: rosemary, chive and thyme.

Some people think that because I am a plant scientist I should also know a lot about gardening. Think again. The extent of my gardening is tending to some house-plants and a few herbs outside. All of these plants are pretty low maintenance (except the parsley, which needs more regular watering). This suits me because I love having plants around, but I tend to be a bit absent-minded about watering them, so I need plants that can tolerate dry conditions, like Aloe vera or thyme.

So why am I NOT an expert gardener? In short, because I’ve not had the years of training and experience that expert gardeners have. My research in plant science uses mostly molecular and cell biology techniques. I didn’t step foot in the greenhouses at my place of work for the whole of the first year of my PhD because I never needed to grow plants in soil. Instead, I was growing plants in sterile conditions (i.e. without microbes like bacteria and fungi) on a jelly-like substance called agar. Continue reading

Saffron: the brightly coloured spice from crocus flowers

Image by Safa Daneshvar (CC-BY-SA-3.0) via Wikimedia Commons

Saffron is made by drying stigmas from Crocus sativus flowers. Image by Safa Daneshvar (CC-BY-SA-3.0) via Wikimedia Commons

Saffron is the world’s most expensive spice by weight. Its vibrant orange-red colour means that as well as being used for flavouring food, it can also be used to dye fabric. Saffron comes from the stigmas (female part) of Crocus sativus flowers. Each stigma is hand-picked, dried and then sold whole or as saffron powder. Since each flower only contains 3 stigmas, around 150,000 flowers are needed to make 1 kg of saffron (1). Continue reading

Tiny orchid seeds need fungi to help them grow

The Orchid family (Orchidaceae) is one of the largest families of flowering plants (alongside the Asteraceae, the daisy family). There are over 26,000 species of orchids with 100-200 new ones discovered every year (1). This is a HUGE number (to put it into perspective there are only around 10,000 bird and 5000 mammal species worldwide).

The early purple orchid is found in UK woodlands and flowers in May. Image by Glyn Baker (CC BY-SA 2.0) via wikimedia commons.

The early purple orchid (Orchis mascula) is found in UK woodlands and flowers in May. Image by Glyn Baker (CC BY-SA 2.0) via Wikimedia Commons.

Orchids are found on every continent except Antarctica in a wide variety of habitats from desert fringes to rainforests. Tropical regions have the richest variety in orchids, most of which grow perched on trees or rocks. A few members of the family such as vanilla are lianas (woody vines) that grow up trees.

Orchids are well-known for their beautiful flowers, but for me, the most fascinating feature of orchids is that they need to form interactions with fungi to be able to grow. Orchid seeds are tiny (less than 1mm long) and contain little or no endosperm (seed energy store) (2). Therefore, to germinate and grow into a mature plant, the seeds need be colonized by friendly fungi, known as mycorrhizal fungi. The fungi provide the main source of carbohydrates (e.g. sugars) for the seedling until it is able to produce its own through photosynthesis. As the chances of an individual orchid seed meeting a suitable mycorrhizal fungus are small, individual orchids can produce millions of seeds (2). Continue reading

The Millennium Seed Bank: saving plants for the future

Cardiospermum halicacabum seeds

Cardiospermum halicacabum seeds. Image by H. Zell (CC BY-SA 3.0) via Wikimedia Commons

To celebrate passing my PhD viva recently my parents gave me an “Adopt a Seed” from the Millennium Seed Bank Partnership, Kew. It was a brilliant present to get me and I was really excited when I received my adoption pack in the post last week. You don’t actually get any seeds when you “Adopt a Seed” but you do get a certificate and a photo, as well as updates on the Millennium Seed Bank.

My adopted seed is from Cardiospermum halicacabum, which originates from tropical America (1). A vine growing up to 3 m long, it has inflated seed capsules that give it the name “love in a puff”. The latin name comes from the Greek kardia (heart) and sperma (seed). I am so excited by my present that I have named C.  halicacabum Organism of the Month here at Plant Scientist. Continue reading

How flooding affects plants

Water from the river Avon flooding a field in front of Sopley Mill (Jan 2014). Photo by Mike Searle (CC BY-SA 2.0) via geograph.org.uk.

Water from the river Avon flooding a field in front of Sopley Mill (Jan 2014). Photo by Mike Searle (CC BY-SA 2.0) via geograph.org.uk.

This winter has been an unusually stormy and wet one for the UK with rainfall for the December-January period being the highest since records began (1). The ground is saturated, and water levels in rivers and lakes have risen leading to flooding in several areas including the Somerset Levels and along the River Thames. Parts of the Somerset Levels have been continuously underwater since December, causing much disruption to the people who live there. But how does flooding affect plants?

The answer is that it depends. Some plants are perfectly happy growing in wet places e.g. bulrushes or water lilies, and are adapted to do so. However, in generally drier areas such as fields or pastures, the presence of excessive amounts of water can cause the plants to become stressed and even die. Continue reading

Camellia sinensis: the plant behind a comforting cup of tea

The organism for February is the plant behind my favourite drink, tea. Camellia sinensis is a shrub native to East, South and Southeast Asia. It is now cultivated across the world in tropical and sub-tropical regions. In 2012 over 4.8 million tonnes of tea produced (1). The plants are harvested by hand every few weeks with only the bud and first 2-3 leaves removed.

By Kristian Frisk (CC-BY-SA-2.0 via Wikimedia Commons)
By Kristian Frisk (CC-BY-SA-2.0 via Wikimedia Commons)

Tea drinking originated in China where, according to legend, the Emperor Shen Nung discovered the drink in 2737 BC (this date seems rather precise to me!) Leaves from Camellia sinensis are processed in different ways to produce different types of tea. To make black tea, the leaves are allowed to oxidise during the drying process resulting in the darkening of the tea leaves as the chlorophyll breaks down and tannins are released. Green tea is made from tea leaves that have undergone minimal oxidation during drying. White tea, which is actually green in colour, is processed in a similar way to green tea, but only the youngest leads and buds are used to make it.

Continue reading