Stephen Blackmore on How Plants Work

All the plants around us today are descended from simple algae that emerged more than 500 million years ago. While new plant species are still being discovered, it is thought that there are around 400,000 species in existence. From towering redwood trees and diminutive mosses to plants that have stinging hairs and poisons, the diverse range of plant life is extraordinary. Stephen Blackmore’s How Plants Work is a fascinating inquiry into, and celebration of, the complex plant kingdom.

Why is the book called How Plants Work?

Too many people overlook the fact that plants are at work all around us. The title helps convey the idea of plants as active players, not just a green background. Our species and other animals could never have evolved if photosynthesis, first in blue green algae,  later in plants, had not made the atmosphere and oceans rich in oxygen. Plants are now known to make up 80% of the living biomass of our planet, and having created the conditions for animal life they are essential for our continued survival as the base of our food chain and as providers of essential ecosystem services.

What attracted you to becoming a botanist?

As a child, I was fascinated by nature and curious about all living things. As such, I wanted to know their names and understand how they lived. At first I was most interested in animals, especially, butterflies, birds and reptiles. As I began to learn more about them I understood that each lived in a specific kind of vegetation, fed on different fruits or seeds, or laid eggs on a particular species of food plant. It dawned on me that plants were at the heart of nature and I wanted to know more about them. I have been fortunate to travel widely as a botanist, collecting plants in several continents.

My own journey led me from studying pollen grains and spores to plant conservation. Pollen fascinated me because each cell-sized grain is an entire male gametophyte plant. I wanted to understand how their enormous diversity of form, surprising since they all perform the same task of delivering the male gametes, originated during their development in the anther. I came to plant conservation through seeing some of the finest forests and grasslands disappearing before our eyes. Botanists are now in a desperate race to save plant diversity to keep the biosphere working.

But, aren’t plants all more or less the same?

Plants are deceptively simple in that they are constructed from so few, very familiar, organs: roots, stems, leaves, and flowers or cones. But within each of these organs there is great diversity of form, a consequence of plants solving such problems as how to live in widely differing environments, from a desert to rain forest. Because they are literally rooted to the spot plants have found ingenious ways to colonize new places, dispersing seeds, pollen, and spores on the wind or harnessing animals to carry them from place to place. A major theme of the book is to explore the diversity of each major organ of the plant and to understand their life cycles and reproduction as products of this diversity.

How were the authors selected?

In bringing together a team to write the book it was important to select world leading botanists, people with the experience as research leaders, and teachers to be able to share their specialist understanding of the workings of different parts of the plant. Just as medical practitioners specialize in different parts of the human body, so botanists focus on investigating specific organs or processes in plants. By engaging such talented botanists, the most authentic information emerges, in a new telling, hopefully resulting in a freshness rarely found in standard textbooks.

What do you hope the book will achieve?

The authors, in sharing their passion for plants, hope to attract people to look more closely at plants and to understand more deeply how diverse they are and how important for our future. Plants, as the source of our food, the foundation of the natural and agricultural landscapes we cherish, are a vital for the future of our species. It matters profoundly to the quality of life in the future that as many people as possible understand the value and importance of plants, as much as their great beauty and endless fascination.

 

Stephen Blackmore is a botanist and conservationist. His books include Green Universe and Plant Conservation Science and Practice. He was the 15th Regius Keeper of the Royal Botanic Garden Edinburgh and was appointed Her Majesty’s Botanist in Scotland in 2010. He is chairman of Botanic Gardens Conservation International and the Darwin Expert Committee.

Plants That Kill: Neem Tree

Adapted from page 217 of Plants That Kill:

Neem, also known as Indian neem, is grown across the tropics and subtropics as a shade tree, for reforestation programmes and in plantations for production of azadirachtin, but is considered invasive in parts of Africa, the Middle East and Australia, where it has become naturalized. The seeds of Philippine neem (Azadirachta excelsa), which is native to Indonesia, Malaysia, Philippines, Papua New Guinea and Vietnam, and has naturalized in Singapore and Thailand, are also a source of neem insecticides. However, even though neem-based pesticides are a good biological alternative to synthetic compounds, accidental ingestion of neem products or seeds has resulted in a number of deaths, especially in children.

While the effectiveness of neem insecticides is directly associated with azadirachtin content, the biological activity of many of the other compounds present in the neem tree (most of which are also triterpenoids of the limonoid group) add to its effect. Used in their natural combination, they may be helpful in mitigating the development of pesticide resistance.

The neem tree (Azadirachta indica) can reach 10–20 m (30–65 ft) in height. It has compound leaves with several pairs of leaflets and heads of 150–250 small white flowers. Photo credit: QpicImages, Alamy Stock Photos

The antifeedant activity of azadirachtin and some of the other neem compounds is through their stimulation of specific ‘deterrent’ cells on the insect mouthparts, while blocking other receptor cells that normally stimulate feeding, resulting in starvation and death of the insect. Insects vary considerably in their behavioural responses to azadirachtin. Studies on the desert locust have shown that it has a particularly high sensitivity to azadirachtin as an antifeedant, being deterred from feeding at concentrations of 0.04 parts per million. Interestingly, North American grasshoppers, including the American grasshopper (Schistocerca americana), which is in the same genus as the desert locust, are insensitive to azadirachtin at such low concentrations. 

Insects that are not deterred from feeding on azadirachtin do not die immediately, but soon stop eating due to the action of the compound on a number of physiological pathways. It interferes with moulting and growth, for example, by blocking production and release of moulting hormones, causing moulting defects, and it disrupts reproduction by reducing the number of viable eggs and live progeny. 

Plants That Kill: A Natural History of the World’s Most Poisonous Plants
By Elizabeth A. Dauncey & Sonny Larsson

This richly illustrated book provides an in-depth natural history of the most poisonous plants on earth, covering everything from the lethal effects of hemlock and deadly nightshade to the uses of such plants in medicine, ritual, and chemical warfare.

Featuring hundreds of color photos and diagrams throughout, Plants That Kill explains how certain plants evolved toxicity to deter herbivores and other threats and sheds light on their physiology and the biochemistry involved in the production of their toxins. It discusses the interactions of poisonous plants with other organisms–particularly humans—and explores the various ways plant toxins can target the normal functioning of bodily systems in mammals, from the effects of wolfsbane on the heart to toxins that cause a skin reaction when combined with the sun’s rays. This intriguing book also looks at plants that can harm you only if your exposure to them is prolonged, the ethnobotany of poisons throughout human history, and much more.

A must for experts and armchair botanists alike, Plants That Kill is the essential illustrated compendium to these deadly and intriguing plants.

  • Provides an authoritative natural history of the most poisonous plants on earth
  • Features hundreds of color illustrations throughout
  • Looks at how and why plants produce toxins
  • Describes the effects of numerous poisonous plants, from hemlock and deadly nightshade to poppies and tobacco
  • Explains poisonous plants’ evolution, survival strategies, physiology, and biochemistry
  • Discusses the uses of poisonous plants in medicine, rituals, warfare, and more

 

Plants That Kill: Ephedera

Adapted from page 214 of Plants That Kill:

The drug ma huang has been one of the most important in the Chinese materia medica for millennia, having been first recorded in Shen-nung Pen-ts’ao Ching (Divine Husbandman’s Materia Medica), the earliest extant Chinese pharmacopoeia (c. ad 25–200). Today, it is sourced from four species of ephedra (Ephedra spp.), including E. sinica, which is native to northeast China, Mongolia and parts of Russia. In fact, at least two-thirds of Ephedra species from across the globe are used medicinally, and are the source of useful compounds in the fight against cold and flu symptoms. Unfortunately, however, they are also subject to abuse.

Chinese ephedra (Ephedra sinica) is a gymnosperm and close relative of conifers, including yews (Taxus spp.). The stems are photosynthetic and the fruit are fleshy cone bracts. Photo credit: WILDLIFE, Alamy Stock Photos

The small genus of Ephedra contains around 54 species within its own family, Ephedraceae, distributed in northern temperate regions of the world as well as in western South America. There is evidence that ephedra may be one of the first plants that was used medicinally, as pollen of medicinal plants, including high-climbing jointfir (E. altissima), was found in the grave of a male Neanderthal buried in Shanidar Cave, Iraq, in around 60,000 bc. Some scientists dispute the interpretation that flowers had been placed deliberately in the grave, however, as the pollen may have been introduced by burrowing rodents. 

Indisputable recorded uses of ephedra in traditional medicine systems include the treatment of asthma, hay fever and other allergies, as well as respiratory diseases such as bronchitis, emphysema, and colds and influenza. The effectiveness of ephedra in treating many of these conditions is not in doubt, but abuse of the active compounds has required their use today to be controlled. 

Ephedra species contain several alkaloids: ephedrine, pseudoephedrine, norephedrine, norpseudoephedrine (cathine), methylephedrine and methylpseudoephedrine. Levels vary tremendously between the species (the North American species Nevada ephedra (E. nevadensis) is apparently devoid of them) and also between plant parts, with the alkaloids concentrated in green stems and leaves, while fruits and roots have virtually none. 

Ephedrine and related alkaloids stimulate the nervous system by mimicking the effects of compounds naturally produced by the body that bind to and activate receptors (endogenous agonists). They are potent stimulators of receptors that are targets for adrenaline (epinephrine) and noradrenaline (norepinephine), and responsible for the ‘fight or flight’ response. The effects of these drugs include constriction of blood vessels (vasoconstriction), raised blood pressure, increased heart rate, expansion of bronchial tubes (bronchodilation), which makes breathing easier, and increase in energy expenditure (thermogenesis). 

The two major alkaloids found in Ephedra species, ephedrine and pseudoephedrine, have been used in decongestant medicines to treat coughs, colds and sinusitis. However, these alkaloids are structurally similar to synthetic amphetamines, with ephedrine differing from methamphetamine only in a hydroxyl group, leading to the use of these medicines in the illicit manufacture of amphetamines. In response, restrictions are generally in place on the sale of products containing the alkaloids. In the United Kingdom, for example, they can legally be sold only at pharmacies, by or under the supervision of a pharmacist, with permitted levels of the alkaloids kept to a minimum if sold without a prescription. 

Restrictions also apply to the sale of the herbal ephedra drug ma huang and others, which have been marketed as ‘herbal ecstasy’. Despite these legal restrictions, the raw herb and products containing ephedra and its alkaloids are still openly sold over the Internet, posing a potential risk to consumers who are unaware of the extremely dangerous side effects.

Plants That Kill: A Natural History of the World’s Most Poisonous Plants
By Elizabeth A. Dauncey & Sonny Larsson

This richly illustrated book provides an in-depth natural history of the most poisonous plants on earth, covering everything from the lethal effects of hemlock and deadly nightshade to the uses of such plants in medicine, ritual, and chemical warfare.

Featuring hundreds of color photos and diagrams throughout, Plants That Kill explains how certain plants evolved toxicity to deter herbivores and other threats and sheds light on their physiology and the biochemistry involved in the production of their toxins. It discusses the interactions of poisonous plants with other organisms–particularly humans—and explores the various ways plant toxins can target the normal functioning of bodily systems in mammals, from the effects of wolfsbane on the heart to toxins that cause a skin reaction when combined with the sun’s rays. This intriguing book also looks at plants that can harm you only if your exposure to them is prolonged, the ethnobotany of poisons throughout human history, and much more.

A must for experts and armchair botanists alike, Plants That Kill is the essential illustrated compendium to these deadly and intriguing plants.

  • Provides an authoritative natural history of the most poisonous plants on earth
  • Features hundreds of color illustrations throughout
  • Looks at how and why plants produce toxins
  • Describes the effects of numerous poisonous plants, from hemlock and deadly nightshade to poppies and tobacco
  • Explains poisonous plants’ evolution, survival strategies, physiology, and biochemistry
  • Discusses the uses of poisonous plants in medicine, rituals, warfare, and more

 

Plants That Kill: White Snakeroot

Adapted from page 191 of Plants That Kill:

When Europeans started to settle in the Midwest region of the United States in the 1800s, they and their livestock began to fall ill. The animals developed violent trembling when they were forced to move or became agitated, and the disease became known as trembles. People who drank the milk of affected animals developed so-called milk sickness, and it is estimated that in some areas of Indiana and Ohio 25–50 per cent of the deaths of early settlers were caused by this condition. One casualty in 1818 was Nancy Hanks Lincoln, whose son, nine years old at the time, would become President Abraham Lincoln. 

Nowadays, human poisoning by white snakeroot (Ageratina altissima) is rare due to industrial milk production, but it is an historically interesting killer plant. Photo credit: Shutterstock, Wiert nieuman

It took some time to identify white snakeroot (Ageratina altissima, syn. Eupatorium rugosum) as the cause of trembles. Although the plant was initially suggested as the culprit in the 1830s, this was only confirmed in the early 1900s. This member of the daisy family (Asteraceae) grows in moist, shaded areas, such as along stream beds and near tree lines. Animals do not show any signs of being poisoned until they have been eating white snakeroot for one to three weeks, and symptoms finally progress to chronic degeneration of the skeletal muscles. Benzofuran ketones, including tremetone, are at least partly responsible for the toxicity of white snakeroot, and they are also found in another member of the daisy family, the rayless goldenrod (Isocoma pluriflora, syn. Haplopappus heterophyllus), which causes a similar disease in grazing animals. 

Plants That Kill: A Natural History of the World’s Most Poisonous Plants
By Elizabeth A. Dauncey & Sonny Larsson

This richly illustrated book provides an in-depth natural history of the most poisonous plants on earth, covering everything from the lethal effects of hemlock and deadly nightshade to the uses of such plants in medicine, ritual, and chemical warfare.

Featuring hundreds of color photos and diagrams throughout, Plants That Kill explains how certain plants evolved toxicity to deter herbivores and other threats and sheds light on their physiology and the biochemistry involved in the production of their toxins. It discusses the interactions of poisonous plants with other organisms–particularly humans—and explores the various ways plant toxins can target the normal functioning of bodily systems in mammals, from the effects of wolfsbane on the heart to toxins that cause a skin reaction when combined with the sun’s rays. This intriguing book also looks at plants that can harm you only if your exposure to them is prolonged, the ethnobotany of poisons throughout human history, and much more.

A must for experts and armchair botanists alike, Plants That Kill is the essential illustrated compendium to these deadly and intriguing plants.

  • Provides an authoritative natural history of the most poisonous plants on earth
  • Features hundreds of color illustrations throughout
  • Looks at how and why plants produce toxins
  • Describes the effects of numerous poisonous plants, from hemlock and deadly nightshade to poppies and tobacco
  • Explains poisonous plants’ evolution, survival strategies, physiology, and biochemistry
  • Discusses the uses of poisonous plants in medicine, rituals, warfare, and more

 

Plants That Kill: Cycads

Adapted from pages 188-189 of Plants That Kill:

The cycads are a group of slow-growing tropical and subtropical palm-like trees that have barely changed since before the time of the dinosaurs – cycad fossils date back to the Late Palaeozoic era, 290–265 million years ago. Their resistance to hurricanes and droughts is part of the reason for their continued survival to the present day. Over the centuries, humans have used cycads for food and medicine, but the toxins they contain mean they have to be processed before they are consumed. Even then, there can be long-term consequences.

Crown of the sago cycad (Cycas revoluta), with a head of developing seeds attached to small leaf-like structures, and surrounded by rigid palm-like leaves up to 1.5 m (5 ft) long. Photo credit: Shutterstock, JT888.

The sago cycad (Cycas revoluta), a member of one of the two families of cycad (Cycadaceae, the other one being Zamiaceae), is often called the ‘sago palm’ but should not be confused with the true sago palm (Metroxylon sagu) in the palm family (Arecaceae). Native to Japan, it is probably the most widely cultivated cycad. Various parts of this and other cycads are eaten by humans, usually when other crops have been destroyed by natural disasters or as a stop-gap during seasonal shortages, but also as a staple part of the traditional diet in many regions. The young leaves may be eaten as a vegetable, but it is the seeds and also the stem pith that are most often used as they, after a long detoxification process, provide a flour with a high starch content.

When Europeans first encountered cycads during their voyages of discovery, they were unaware of their toxicity. During Captain James Cook’s first voyage to Australia in 1770, the botanist Joseph Banks noticed that several crew members became violently ill after eating nuts from Cycas media, and General Jan Smuts and his troops fell foul of the breadpalm (Encephalartos longifolius, Zamiaceae) during the Boer War. In Honduras, it has been documented that the roots of camotillo (Zamia furfuracea, Zamiaceae) were used in unlawful poisonings. Improper processing of cycad plants before consumption, either as a food or traditional remedy, leaves the azoxymethanol glycosides they contain at toxic levels and is now the usual cause of acute poisoning. A second toxin, beta-methylamino-L-alanine (BMAA), which is particularly concentrated in the seeds and root nodules, is not removed by the processing, but only takes effect if the plant is eaten on repeated occasions. 

Plants That Kill: A Natural History of the World’s Most Poisonous Plants
By Elizabeth A. Dauncey & Sonny Larsson

This richly illustrated book provides an in-depth natural history of the most poisonous plants on earth, covering everything from the lethal effects of hemlock and deadly nightshade to the uses of such plants in medicine, ritual, and chemical warfare.

Featuring hundreds of color photos and diagrams throughout, Plants That Kill explains how certain plants evolved toxicity to deter herbivores and other threats and sheds light on their physiology and the biochemistry involved in the production of their toxins. It discusses the interactions of poisonous plants with other organisms–particularly humans—and explores the various ways plant toxins can target the normal functioning of bodily systems in mammals, from the effects of wolfsbane on the heart to toxins that cause a skin reaction when combined with the sun’s rays. This intriguing book also looks at plants that can harm you only if your exposure to them is prolonged, the ethnobotany of poisons throughout human history, and much more.

A must for experts and armchair botanists alike, Plants That Kill is the essential illustrated compendium to these deadly and intriguing plants.

  • Provides an authoritative natural history of the most poisonous plants on earth
  • Features hundreds of color illustrations throughout
  • Looks at how and why plants produce toxins
  • Describes the effects of numerous poisonous plants, from hemlock and deadly nightshade to poppies and tobacco
  • Explains poisonous plants’ evolution, survival strategies, physiology, and biochemistry
  • Discusses the uses of poisonous plants in medicine, rituals, warfare, and more

Plants That Kill: Ackee

Adapted from pages 158-159 of Plants That Kill:

Although it has also been introduced to the other Caribbean islands, Central America and Florida, ackee is widely eaten only on Jamaica. In fact, it is Jamaica’s national fruit, and ackee and saltfish is the national dish. The leathery fruit are 7.5–10 cm (3–4 in) long, bright red or yellow-orange when ripe, and split open into three sections to expose three shiny black seeds, each surrounded by a large yellow or whitish aril. Only arils from ripe fruit that have naturally split open are eaten. To remove any residual toxicity, they are cleaned of all red fibre (the aril membrane) and boiled, and the water they are boiled in is discarded. Cooking unripe arils does not destroy their toxicity.

The ackee tree (Blighia sapida) has pairs of glossy leaves. Its fruit ripen to red and, when they split open, the cream arils within can be eaten after cooking.
Photo credit: Shutterstock, twiggyjamaica

Before the toxicity of ackee was understood, eating unripe arils frequently caused poisoning known as Jamaican vomiting sickness, which occurred as an annual epidemic. Symptoms included vomiting, convulsions and, frequently, also coma and death, with mortalities being more common in children, particularly those already suffering from malnutrition. The underlying cause was eventually linked to the consumption of unripe ackee arils. This results in low blood sugar levels (hypoglycaemia) through a blockade of the liver’s ability to synthesize glucose and a reduction in fatty acid metabolism (both normal routes for increasing levels of blood sugar), as well as depletion of the liver’s carbohydrate reserves. 

Poisoning is due to the presence of an amino acid derivative, hypoglycin A (2-amino-3-(methylenecyclopropyl)- propionic acid), which is also found in other plants of the soapberry family, such as lychee (Litchi chinensis). In ackee, the concentration of hypoglycin A is high in unripe arils and reduces significantly as they ripen, although low levels remain in the aril membrane. The seeds also contain the less toxic hypoglycin B (the gamma-glutamyl conjugate of hypoglycin A), with concentrations significantly increasing as the seeds ripen. 

Plants That Kill: A Natural History of the World’s Most Poisonous Plants
By Elizabeth A. Dauncey & Sonny Larsson

This richly illustrated book provides an in-depth natural history of the most poisonous plants on earth, covering everything from the lethal effects of hemlock and deadly nightshade to the uses of such plants in medicine, ritual, and chemical warfare.

Featuring hundreds of color photos and diagrams throughout, Plants That Kill explains how certain plants evolved toxicity to deter herbivores and other threats and sheds light on their physiology and the biochemistry involved in the production of their toxins. It discusses the interactions of poisonous plants with other organisms–particularly humans—and explores the various ways plant toxins can target the normal functioning of bodily systems in mammals, from the effects of wolfsbane on the heart to toxins that cause a skin reaction when combined with the sun’s rays. This intriguing book also looks at plants that can harm you only if your exposure to them is prolonged, the ethnobotany of poisons throughout human history, and much more.

A must for experts and armchair botanists alike, Plants That Kill is the essential illustrated compendium to these deadly and intriguing plants.

  • Provides an authoritative natural history of the most poisonous plants on earth
  • Features hundreds of color illustrations throughout
  • Looks at how and why plants produce toxins
  • Describes the effects of numerous poisonous plants, from hemlock and deadly nightshade to poppies and tobacco
  • Explains poisonous plants’ evolution, survival strategies, physiology, and biochemistry
  • Discusses the uses of poisonous plants in medicine, rituals, warfare, and more

 

Plants That Kill: Capsaicin

Adapted from pages 122-123 of Plants That Kill:

The fruit and seeds of species of chilli peppers (Capsicum spp.) in the potato family (Solanaceae) contain a pungent compound, capsaicin, that makes food ‘hot’. As well as being used by humans as a spice for thousands of years, capsaicin also has medicinal applications, and the burning discomfort and pain it causes have found roles in riot-control and self-defence. 

The chilli or chili pepper (Capsicum annuum) is a small shrub from Mexico and Guatemala, with simple leaves and pendant, star-shaped flowers that appear singly and are followed by elongated, brightly coloured fruit. Numerous cultivars have been bred that vary in the size, shape and pungency of these fruit. They include the large, sweet bell peppers, as well as mild to hot chilli peppers. The taxonomy of chillies is complicated, however, with some cultivars of C. annuum having characteristics that overlap with those of two other species, the Tabasco pepper (C. frutescens) from Bolivia and western Brazil, and the very hot bonnet pepper (C. chinense), which despite its specific epithet is from Bolivia, northern Brazil and Peru. Some prefer to treat these three species and their cultivars as the ‘annuum–chinense– frutescens complex’. 

To alleviate the ‘heat sensation’ from chilli, try eating a yogurt raita containing chopped mint (Mentha spp.) leaves, as the menthol from the mint stimulates ‘cold sensation’ neurons. Photo credit: one photo, Shutterstock

Some culinary traditions use more chilli pepper than others, with the highest number being eaten in the species’ native Mexico (one chilli per person per day). Chilli has also been embraced in many of the countries to which it has been introduced, particularly India, where it is a key ingredient in curries, and Thailand. Either the fresh fruit and seeds, or the powdered or flaked dried fruit, are used for seasoning during cooking or as a condiment. 

The pungent compounds in chilli peppers, including capsaicin (8-methyl-N-vanilloyl-6-nonenamide), are capsaicinoid alkaloids, which bind to vanilloid receptors on sensory neurons (known as transient receptor potential vanilloid (TRPV) channels). These same receptors can also be stimulated by heat and pain, so the binding of the capsaicin results in the sensation of heat. The degree of burning and reddening is related to the concentration of capsaicinoids (see box) and duration of exposure (a dose-related response). TRPV channels are common to all mammals, and thereby deter rodents and other mammalian pests from eating chilli crops. Birds lack the capsaicin-binding site of these channels, however, so eat the ripe red fruit and disperse the seeds without harm. 

In addition to the sensation of heat and burning in the mouth, eating large amounts of hot chillies can cause irritation of the gastrointestinal tract. It is the burning discomfort and pain that chillies or concentrated chilli extracts cause to the eyes and nose that can be most distressing. Pepper sprays have proved to be effective weapons since they were first employed by Mayan Indians, and police forces in a number of countries now use them in the control of unruly individuals and crowds. However, the legality of using pepper sprays for self-defence varies around the world. 

Plants That Kill: A Natural History of the World’s Most Poisonous Plants
By Elizabeth A. Dauncey & Sonny Larsson

This richly illustrated book provides an in-depth natural history of the most poisonous plants on earth, covering everything from the lethal effects of hemlock and deadly nightshade to the uses of such plants in medicine, ritual, and chemical warfare.

Featuring hundreds of color photos and diagrams throughout, Plants That Kill explains how certain plants evolved toxicity to deter herbivores and other threats and sheds light on their physiology and the biochemistry involved in the production of their toxins. It discusses the interactions of poisonous plants with other organisms–particularly humans—and explores the various ways plant toxins can target the normal functioning of bodily systems in mammals, from the effects of wolfsbane on the heart to toxins that cause a skin reaction when combined with the sun’s rays. This intriguing book also looks at plants that can harm you only if your exposure to them is prolonged, the ethnobotany of poisons throughout human history, and much more.

A must for experts and armchair botanists alike, Plants That Kill is the essential illustrated compendium to these deadly and intriguing plants.

  • Provides an authoritative natural history of the most poisonous plants on earth
  • Features hundreds of color illustrations throughout
  • Looks at how and why plants produce toxins
  • Describes the effects of numerous poisonous plants, from hemlock and deadly nightshade to poppies and tobacco
  • Explains poisonous plants’ evolution, survival strategies, physiology, and biochemistry
  • Discusses the uses of poisonous plants in medicine, rituals, warfare, and more

 

Plants That Kill: The Little Apple of Death

Adapted from page 118 of Plants That Kill:

The manchineel tree is found from the coast of Mexico south through Central America to Colombia and Venezuela, as well as in the West Indies and Florida. Its caustic properties soon became known to European explorers of the New World, who encountered the tree on beaches. In the sixteenth century, Oviedo noted its danger in his book on the natural history of the West Indies (which incidentally also included the first illustration of a pineapple): 

It has been proved many times that if men carelessly lie down to sleep under the trees, when they rise after a short nap there is a great pain in the head and swelling of the eyes and cheeks. And if by chance the dew from the tree falls on the face, it is like fire, blistering and burning the skin wherever it touches; and if it falls in the eye it blinds or burns them, and the sight is endangered. If the wood is burned no one can endure it long, for it causes much heaviness, and such headaches that all stand away from it, be they man or any other animal.

Leafy branches and immature fruit of the manchineel (Hippomane mancinella), also known as manzanita de la muerte, literally ‘little apple of death’, are a risk for unwary visitors to tropical beaches. Photo Credit: Rob Matthews, Alamy Stock Photo

Since then, numerous graphic accounts of the symptoms that result from skin or eye contact with the latex of the manchineel tree have been published, so we can be left in no doubt of the harm the species can cause. In addition, it produces deceptively apple-like fruit, which are 3–5 cm (1–2 in) in diameter, and when ripe are yellowish green with flushed red cheeks and an aromatic, pleasant-tasting yellow flesh. These, too, can cause contact reactions, and eating the fruit is even more disastrous, as doing so irritates the mouth, throat and digestive tract; deaths have occurred.

Plants That Kill: A Natural History of the World’s Most Poisonous Plants
By Elizabeth A. Dauncey & Sonny Larsson

This richly illustrated book provides an in-depth natural history of the most poisonous plants on earth, covering everything from the lethal effects of hemlock and deadly nightshade to the uses of such plants in medicine, ritual, and chemical warfare.

Featuring hundreds of color photos and diagrams throughout, Plants That Kill explains how certain plants evolved toxicity to deter herbivores and other threats and sheds light on their physiology and the biochemistry involved in the production of their toxins. It discusses the interactions of poisonous plants with other organisms–particularly humans—and explores the various ways plant toxins can target the normal functioning of bodily systems in mammals, from the effects of wolfsbane on the heart to toxins that cause a skin reaction when combined with the sun’s rays. This intriguing book also looks at plants that can harm you only if your exposure to them is prolonged, the ethnobotany of poisons throughout human history, and much more.

A must for experts and armchair botanists alike, Plants That Kill is the essential illustrated compendium to these deadly and intriguing plants.

  • Provides an authoritative natural history of the most poisonous plants on earth
  • Features hundreds of color illustrations throughout
  • Looks at how and why plants produce toxins
  • Describes the effects of numerous poisonous plants, from hemlock and deadly nightshade to poppies and tobacco
  • Explains poisonous plants’ evolution, survival strategies, physiology, and biochemistry
  • Discusses the uses of poisonous plants in medicine, rituals, warfare, and more

Plants That Kill: Deadly nightshade, black henbane & witchcraft

Adapted from page 81 of Plants That Kill:

Deadly nightshade (Atropa bella-donna) is a herbaceous perennial that dies back to a rootstock every year but can grow into a substantial plant during the summer. Attractive, juicy black berries follow its solitary bell-shaped purplish flowers, and conspicuous green sepals form a star at the base. Deadly nightshade grows naturally in Europe, west Asia and north Africa. In northern Europe it is particularly found on chalky soils and close to former abbeys and monasteries, where it was grown as a medicinal plant during the Middle Ages.

Black henbane (Hyoscyamus niger) is native to much of Eurasia and is now widely distributed in temperate regions. Photo credit: A_lya, Shutterstock.

Deadly nightshade is just one of the tropane alkaloid-containing plants that are inextricably linked to tales of witchcraft. Together with mandrakes (Mandragora spp.) and henbane (Hyoscyamus spp.), it is said to have been an ingredient of an ointment used by witches to give them the sensation of flying, and is why witches are often depicted on broomsticks. 

One of the most recent deaths from deadly nightshade, of which there are actually very few, was of a modern-day witch who went by the name of Robert Cochrane. He lived in Slough, United Kingdom, where he started a coven known as the Clan of Tubal Cain, based on a combination of Celtic mysticism and village witchcraft philosophy (American branches are known as the ‘1734 tradition’). Cochrane died nine days after the eve of the summer solstice in 1966, seemingly after having ingested deadly nightshade leaves and sleeping tablets. The inquest into his death returned a verdict of suicide with deadly nightshade. In some witchcraft circles it is believed that Cochrane had appointed himself as a male sacrifice.

Plants That Kill: A Natural History of the World’s Most Poisonous Plants
By Elizabeth A. Dauncey & Sonny Larsson

This richly illustrated book provides an in-depth natural history of the most poisonous plants on earth, covering everything from the lethal effects of hemlock and deadly nightshade to the uses of such plants in medicine, ritual, and chemical warfare.

Featuring hundreds of color photos and diagrams throughout, Plants That Kill explains how certain plants evolved toxicity to deter herbivores and other threats and sheds light on their physiology and the biochemistry involved in the production of their toxins. It discusses the interactions of poisonous plants with other organisms–particularly humans—and explores the various ways plant toxins can target the normal functioning of bodily systems in mammals, from the effects of wolfsbane on the heart to toxins that cause a skin reaction when combined with the sun’s rays. This intriguing book also looks at plants that can harm you only if your exposure to them is prolonged, the ethnobotany of poisons throughout human history, and much more.

A must for experts and armchair botanists alike, Plants That Kill is the essential illustrated compendium to these deadly and intriguing plants.

  • Provides an authoritative natural history of the most poisonous plants on earth
  • Features hundreds of color illustrations throughout
  • Looks at how and why plants produce toxins
  • Describes the effects of numerous poisonous plants, from hemlock and deadly nightshade to poppies and tobacco
  • Explains poisonous plants’ evolution, survival strategies, physiology, and biochemistry
  • Discusses the uses of poisonous plants in medicine, rituals, warfare, and more

 

Plants That Kill: Apocynaceae

Adapted from page 52 of Plants That Kill:

The dogbane family is one of the larger families of flowering plants, and is today considered to contain more than 5,000 species in 366 recognized genera, including those that have, at times, been placed in their own family, Asclepiadaceae. The almost globally distributed Apocynaceae (only northern regions lack native species) has adapted to almost all environments and contains a large diversity of plant forms. 

Species grow as herbs, climbers and lianas, succulents or trees. The flowers are often showy or conspicuous in form or smell, and many species have evolved special structures for pollen dispersal, such as pollinia, coherent masses of pollen grains that are transferred to the next plant by sticking to insect pollinators. These structures are especially elaborate in milkweeds (Asclepias spp.), waxflowers (Hoya spp.) and their relatives, constituting a feature that allows easy placement of these plants within the family (although deciding on the actual genus and species can be quite difficult).

Elephant vine (Strophanthus amboensis) is found from Zaire to Namibia and contains cardioactive steroids. The petals are fused to form a cup at the base and there are five spreading, elongated lobes.

The large number of species and wide geographical distribution of the dogbane family makes it easy to understand why so many plants are used by humans. The showy, waxy flowers of frangipani (Plumeria spp.) have found a place as a constituent in Polynesian lei garlands, the fibres from dogbane (Apocynum cannabinum) have been used to make cloth and string, some species are used in religious rituals, and some genera, such as Landolphia, were briefly important as sources of rubber in the late nineteenth and early twentieth centuries. Several plants in the family have been used as arrow poisons or in traditional medicinal systems, and the Madagascar periwinkle (Catharanthus roseus) is the source of an important cancer drug. 

It seems that most plants in the dogbane family are toxic to some degree, but the reason for this differs between groups of species. Some groups produce cardioactive steroids as the toxic principle, while others produce monoterpene indole alkaloids. Accordingly, the family presents several toxidromes, the combined picture of symptoms in poisonings, with some presenting as acute heart failure with arrhythmias and others giving signs of detrimental effects on the nervous system – for example, seizures, paralysis and hallucinations. As members of the dogbane family are widely distributed and many produce fatal intoxications, the use of these plants in suicides and poisonings is not uncommon in certain regions of the world.

Plants That Kill: A Natural History of the World’s Most Poisonous Plants
By Elizabeth A. Dauncey & Sonny Larsson

This richly illustrated book provides an in-depth natural history of the most poisonous plants on earth, covering everything from the lethal effects of hemlock and deadly nightshade to the uses of such plants in medicine, ritual, and chemical warfare.

Featuring hundreds of color photos and diagrams throughout, Plants That Kill explains how certain plants evolved toxicity to deter herbivores and other threats and sheds light on their physiology and the biochemistry involved in the production of their toxins. It discusses the interactions of poisonous plants with other organisms–particularly humans—and explores the various ways plant toxins can target the normal functioning of bodily systems in mammals, from the effects of wolfsbane on the heart to toxins that cause a skin reaction when combined with the sun’s rays. This intriguing book also looks at plants that can harm you only if your exposure to them is prolonged, the ethnobotany of poisons throughout human history, and much more.

A must for experts and armchair botanists alike, Plants That Kill is the essential illustrated compendium to these deadly and intriguing plants.

  • Provides an authoritative natural history of the most poisonous plants on earth
  • Features hundreds of color illustrations throughout
  • Looks at how and why plants produce toxins
  • Describes the effects of numerous poisonous plants, from hemlock and deadly nightshade to poppies and tobacco
  • Explains poisonous plants’ evolution, survival strategies, physiology, and biochemistry
  • Discusses the uses of poisonous plants in medicine, rituals, warfare, and more

Plants That Kill: Aconite alkaloids

From hemlock and deadly nightshade to poppies and tobacco, poisonous plants have long been used in medicine, rituals, and even warfare. For the next few months, Princeton Nature will be taking a closer look at the evolution, survival strategies, physiology, and biochemistry of the most toxic plants on Earth. Pulling from Elizabeth A. Dauncey & Sonny Larsson’s new book, Plants That Kill, we hope to provide you with just a sample of the deadly and intriguing plants that can be found in this gorgeously illustrated book.

Adapted from page 48-49 of Plants That Kill:

Aconite alkaloids are mostly restricted to a small number of genera in the buttercup family, particularly the aconites (Aconitum spp.) and their close relatives the larkspurs (Delphinium spp.). The presence of the compounds seems to give these plants a strong evolutionary advantage, as the group constitutes about a third of all species within the family. Aconites and larkspurs produce these highly toxic compounds from a substance called geranylgeranyl diphosphate, which is an essential part of the chlorophyll needed for photosynthesis. They can be grouped into three different ‘flavors’, called veatchine, atisine and aconitine alkaloids. The compounds in the last of these groups are the most toxic, which is thought to be due to their ability to pass through fat-containing barriers such as cell membranes and also the skin. This explains why gardeners and florists who, with bare hands, handle the cut stems or crushed material of aconite and larkspur plants in large amounts or for extended periods of time may experience mild symptoms of tingling or numbness.

There are around 250 species of aconite (Aconitum spp.) found in the wild in the northern hemisphere, but they are also widely grown in temperate gardens and sold as cut flowers.                              Photo credit: Alex Polo, Shutterstock

Species of aconite are used to treat joint pain in traditional Chinese herbal medicine in the form of bath additives, rubs and ointments. Their alkaloids can be absorbed through the skin, where they act as local anaesthetics. They may also be taken orally to treat asthma, gastroenteritis and various tumours, or as a supportive and revitalizing tonic. How is this possible, when these plants are very poisonous and small amounts can cause dangerous, or even lethal, effects on the heart and respiratory muscles? 

Before use, the raw material must be subjected to pao zhi (a detoxifying measure), which might include heating and/or soaking with the intention of ensuring maximal therapeutic efficacy with minimal adverse effects. During such processes, the toxic alkaloids are transformed into less harmful compounds, explaining why aconite use has persisted in spite of its high risk of poisoning. However, even though pao zhi is usually performed, a number of patients who take traditional Chinese aconite medicines are hospitalized each year due to poisoning. 

Plants That Kill: A Natural History of the World’s Most Poisonous Plants
By Elizabeth A. Dauncey & Sonny Larsson

This richly illustrated book provides an in-depth natural history of the most poisonous plants on earth, covering everything from the lethal effects of hemlock and deadly nightshade to the uses of such plants in medicine, ritual, and chemical warfare.

Featuring hundreds of color photos and diagrams throughout, Plants That Kill explains how certain plants evolved toxicity to deter herbivores and other threats and sheds light on their physiology and the biochemistry involved in the production of their toxins. It discusses the interactions of poisonous plants with other organisms–particularly humans—and explores the various ways plant toxins can target the normal functioning of bodily systems in mammals, from the effects of wolfsbane on the heart to toxins that cause a skin reaction when combined with the sun’s rays. This intriguing book also looks at plants that can harm you only if your exposure to them is prolonged, the ethnobotany of poisons throughout human history, and much more.

A must for experts and armchair botanists alike, Plants That Kill is the essential illustrated compendium to these deadly and intriguing plants.

  • Provides an authoritative natural history of the most poisonous plants on earth
  • Features hundreds of color illustrations throughout
  • Looks at how and why plants produce toxins
  • Describes the effects of numerous poisonous plants, from hemlock and deadly nightshade to poppies and tobacco
  • Explains poisonous plants’ evolution, survival strategies, physiology, and biochemistry
  • Discusses the uses of poisonous plants in medicine, rituals, warfare, and more

 

Anurag Agrawal: Monarchs & Milkweed in Mexico

Greetings monarch and milkweed enthusiasts from Mexico. This is Part II in my series from Oaxaca, where I am based on sabbatical leave from Cornell (see the first post here). This post follows up on the inspiration I am gaining on sabbatical and is an entryway for my next research and writing projects, following up on my recent book Monarchs and Milkweeds. I expect that the next post will be a detour from this series, as the overwintering numbers of monarch butterflies will soon be announced by the World Wildlife Fund – and this will provide an opportunity to reflect on monarch population trends (are they still declining?) (see last year’s post on the population here).

Oaxaca city is a bustling cultural and culinary capital, tropical, yet it sits at mid-elevation around 5000 ft above sea level.  January is the beginning of the dry season, with many trees beginning to lose their deciduous leaves.  And the “weedy” milkweed of Mexico, analogous to the common milkweed (Asclepias syriaca) of the eastern USA, is blood flower, sometimes called tropical milkweed, Asclepias curassavica.  This species, however, needs moisture and protection from the intense, constant and direct sunlight loved by many other milkweeds.  Here in the middle of the city, where a stream provides both moisture and shade, blood flower is abundant and apparently always in flower.  Hundreds of plants are along this corridor.

Although hundreds of millions of butterflies are currently overwintering in Michoacán (within the Monarch Butterfly Biosphere Reserve), here in Oaxaca, monarchs have a year-around (and apparently non-migratory) population. Adult butterflies were abundant in this stream corridor in January as were many eggs and large caterpillars.

This caterpillar found a quite spot away from milkweed to molt (change its exoskeleton to the larger size).

Butterflies fluttered, twirled around in mating behavior, and females could be seen curling their abdomens in preparation for laying an egg. The fact that non-migratory monarchs are abundant in the city of Oaxaca gives me pause.  I am not sure how long this has been the case.  Are these butterflies a reservoir for the declining migratory butterflies?

In the mid-elevation grasslands on the edge of town, this rare spring flowering milkweed was blooming early. Formerly known as Asclepias rosea, and now renamed to Asclepias senecionifolia (“the milkweed with leaves like Senecio”), it is pretty small and has feathery fine leaves.

This individual has the oleander aphid on it, feeding away (see yellow bugs in the center) and 5 (!) butterfly eggs.  I wasn’t sure which species of butterfly, until I noticed the plant next door.

This mature caterpillar is not a monarch, and I cannot quite tell if it is a “Soldier” Danaus eresimus or a “Queen” Danaus gillipus. Some of the closest relatives of our beloved monarch. Note that although the monarch has two pairs of tentacles, the soldier and queen sports three pairs, likely to sense the sounds, vibrations, and other aspects of its local environment.

As noted in the first post, the nodding milkweed, Asclepias glaucescens, a robus and waxy milkweed can be common in the region.

The creamy white (and large!) flower of the nodding milkweed, Asclepias glaucescens.

 

Leaves can be green to purple, and the prominent venation shows the canals that hold pressurized latex.

Break a leaf and experience the thick and toxic goo.  Both this species and the A. senecionifolia above exude large quantities of latex.

Before I encountered butterflies or caterpillars on the nodding milkweed, I came across this “bug” (a true bug, as it were, in the insect group Hemiptera). Note the highly contrasting red and deep blue, a classic advertisement of the toxic milkweed insects. Colleagues Georg Petschenka and Jürgen Deckert helped identify this as an immature of Largus species. This reminded me that I had previously found a Largus species associated with Asclepias linaria in northern Mexico about a decade ago.  We currently don’t know the extent to which Largus is specialized on milkweed (versus eating other plants) or whether it gains toxicity by sequestering milkweed’s toxins. Perhaps a good PhD dissertation for one my students!

Egg dumping!  This nodding milkweed had, count them, over 9 eggs, an unusual phenomenon for monarchs.  But I didn’t know if these were monarch or solider/queen eggs.  I suspected soldier because I had found solider caterpillars nearby (see above). Nonetheless, after they hatched a few days later, it was clear, they were monarchs!

Nonetheless, I found another soldier/queen caterpillar on a neighboring plant. Note the notch in the leaf made by a caterpillar (the vein drain!)

The soldier (or queen!) in all its glory.

Among the 25 or so nodding milkweeds I found, I came to realize that more than one Danaus species were coexisting. Several caterpillars of each species intermingled.  It is unclear the extent to which butterflies and caterpillars recognize each other as similar or different species, and what ecological consequence this has.  Do they compete?

And lastly, on the nodding milkweed Asclepias glaucescens, were these green aphids.  Not the oleander aphid found on A. senecionifolia above. Some ants collected their sugary excrement, but they were not so heavily tended.  The species identity and relationship with milkweed are unknown.

Later last week, I went on a hike to San Pablo Cuatro Venados, a close by community that sits near the top of a ridge (around 9000 ft above sea level) that forms the western wall of the Oaxaca Valley.  It was chili at the start of the hike, with thin mountain air along the 10 km trek on a dusty dry dirt road.  Just as we were turning around, I noticed this dusty purplish plant.  I instantly knew it was one of the rarer highland milkweeds.

The spectacular but confusing Asclepias melantha. Confusing only because I did not expect to see it flowering until the beginning of the rainy season in June or July.

Note the petals of Asclepias melantha. Although milkweed petals are often “reflexed”, or pushed back to give the flower a rocket-like appearance (see A. senecionifolia above), these petals form a cup around the rest of the flower.  The flowers of Asclepias glaucescens above are not reflexed either, but are less cup-like.

Back at lower elevation in the grasslands, this Asclepias oenotheroides (“looking like Oenothera”) had multiple butterfly eggs.  This species, known as zizotes milkweed, is common the south-central USA and all the way down here in Oaxaca.

Flowers of zizotes milkweed, Asclepias oenotheroides.

A large monarch caterpillar munching away on zizotes milkweed, Asclepias oenotheroides.

 

Alas, I thought I would have a butterfly, but here, as in so many other places, parasites like this fly larva got the best of the caterpillar! These flies are “parasitoids” who lay an egg in a caterpillar and then eat them from the inside out.

 

Anurag Agrawal (photographed, left, with a Malagasy elephant milkweed [Pachypodium] in downtown Oaxaca, Mexico) is a professor in the Department of Ecology and Evolutionary Biology and the Department of Entomology at Cornell University.

 

He lives in Ithaca, New York. For more information, see his blog, publications, and multi-media on monarchs and milkweed.