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
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