One Man's Poison

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Contents

Introduction:

Cycads are plants of many contrasts, great giants to bonsai-like midgets, with palm-like trunks or without any apparent stems at all, occurring in lush forests to semi-deserts, with smooth delicate leaves to tangled barbs more effective than any anti-personnel fencing! So it shouldn't come as a great surprise to find a contrast of edible and poisonous properties, often in the same species.

Cycads have been used as a source of food starch, particularly during times when normal food supplies have been curtailed, for many years in different parts of the world. The "arrowroot" starch, whilst generally obtained from the rhizomes of Marantha species, can also be extracted from the underground stems of Zamia floridana. "Sago" starch is derived from the stems of certain palms and various Cycas Zamia and Macrozamia spp. The Cape Hottentot peoples were fond of scooping out the pith from the trunk of Encephalartos spp. (especially longifolius), after which they tied it up in animal skins, buried these for a few weeks then kneaded the product into a paste which baked to give a palatable form of bread - hence the name Broodboom. (Readers are not advised to attempt to follow this recipe!)

Since most mature cycads produce large numbers of fairly sizeable seeds, it is not surprising that these too have been used as a food source. But many found out to their cost that the starch and protein-rich kernels of most cycads contain a dangerous poison with both acute and chronic toxicological properties. That fascinating book by Denys Reitz, 'Commando', tells the story of how General J.C. Smuts and his men were camped in the Zuurberg mountains with food supplies running low and the British troops nearby.

"... the men had little or no food with them and were already beginning to feel hungry. Scattered about stood a strange growth known as 'Hottentot's bread' (then reported as E. altensteinii but thought now to be E. longifolius), a wild fruit not unlike a large pineapple... one of the men sampled it and found it to his liking . . . many unfortunately followed suit. " Reitz then goes on to say "I was astonished to find more than half our men groaning and retching on the ground in agony, some apparently at their last gasp. General Smuts was worse than the rest, so, with half our number out of action, we were also leaderless, for he was lying comatose... our position was critical... Commandant van Deventer was too ill to take charge... the sick men were worse than ever... However, as the darkness slowly passed, one man after another recovered sufficiently to stagger to his feet, and towards dawn there were not more than twenty unable to stand. General Smuts was still prostrate... he gave orders that the men who could not help themselves were to be tied to their saddles and that the Commando was to march deeper into the mountains. "

Smuts and his colleagues were lucky to survive. In 1912, two Mpondo children died at Tabankulu after eating seeds thought to be from E. villosus. Yet it appears that the outer fleshy part of the seed is relatively free from poison. Baboons, monkeys and dassies eat this part with impunity, and the pulp of the modjadji cycad is occasionally eaten by the locals in the E. Transvaal. Many birds enjoy the outer flesh too; Giddy describes how the Trumpeter Hornbill, commort in coastal areas, swallows seeds of E. ferox whole, later regurgitating the intact kernel. She believes this to be significant factor in the spread of the species, often found immediately below the convenient perches afforded by the branches of the Umdoni tree. The natural product chemists have extracted and analysed the toxins and found them to be rather unusual compounds called azoxyglycosides. Macrozamin is the one found in Macrozamia spiralis and M. riedle, Bowenia serrulata, Cycas media and Encephalartos barkeri, E. hildebrandtii, E. transvenosus and E. lanatus. Cycasin, closely related chemically, is found in Cycas revoluta and C. thouarsii.

It is remarkable that many indigenous people in different parts of the world have quite independently found out how to detoxify the seed. All 'recipes' are based on steeping the crushed seeds in water which slowly breaks down and dissolves out the poison. Members of Captain Cook's party told how the Australian aboriginals harvest seed of Cycas media, pound it up and dry it, then soak it in a stream for 4 to 5 days, after which it is made into a paste and baked into bread. In 1788, Governor Phillips of New South Wales reported a similar process was used to render the seeds of Macrozamia spiralis (the 'burrawang') harmless. More recently this species has been used for alcohol production, manufacture of laundry starch and the production of adhesive pastes. Who says cycads aren't versatile?

Closer to home, Medley Wood (of E. woodii fame) tells how the Zulu people have soaked cycad seeds in water and successfully removed the toxin. The problem is that 100% removal of the poison can never be guaranteed. It is now thought that the high incidence of amyotropic lateral sclerosis on the island of Guam is directly caused by the improperly-processed seeds of Cycas species consumed by the inhabitants.

Another, rather different, problem arises from poisons in cycad leaves. Grazing by stock on leaves of certain Macrozamia species in Australia and Zamia species in the Americas has resulted in partial or total paralysis of the hind legs, a condition known as the 'wobbles' or 'staggers'. Whilst this rarely kills the animals, they are unable to obtain more food and water and thus perish as a result. The Australian Government has embarked on quite extensive programmes to eradicate the offending species, particularly Macrozamia moorei, but fortunately a specific reservation has been set aside to prevent this very attractive species becoming extinct. Very luckily, our Encephalartos leaves are free of this toxin.

Not all parts, and not all species, have been fully investigated for toxic effects. The Veterinary Research Institute at Onderstepoort has been doing some research into South African cycad toxicity and reports that poisons are almost certainly present in the kernels and possible to a lesser concentration in the outer flesh, of seeds of E. cycadifolius, E. eugene-maraisii, E. horridus, E. ferox, E. lehmannil, E. longifolius, E. laevifolius, E. lebomboensis, E. umbeluziensis and E. villosus. Dr. Tustin gives the sound advice that "ingestion of any parts of plants of Encephalartos is potentially fraught with danger and should be strenuously discouraged". In the unlikely event of accidental consumption, the immediate first-aid step would be to induce vomiting. The patient should drink a glass of warm water and the 'finger-down-the-throat' technique used. Qualified medical attention should be sought immediately.

References:

1. C.J. Chamberlain: "The Living Cycads", Hafner Publishing Co. (1919, reprinted 1969).

2. Cynthia Giddy: "Cycads of South Africa" C. Struik Publishers, Second Edition (1984).

3. R. HEGNAUER: "Chemotaxonomie der Pflanzen" Band I, Birkhauser Verlag (1962).

4. R.S. Palekar & D.K. Dastur, Nature, June 26, 1965, 1363-1365.

5. Denys Reitz: "Commando - a Boer Journal of the Boer War" Faber & Faber (1929, reprinted 1969).

6. D.G. Steyn, S.J. Van Der Walt & I. Verdoorn, S.A. Medical Journal, 11 December 1948, 758 760.

7. J.W. Thieret, Economic Botany, Vol. 12, No. 1, 1958, 3-41.

8. R.C. Tustin, S.A. Medical Journal, 23 Nov., 1974, 2369-2373.

9. J.M. Watt & Mg. Breyer-Brandwijk: "The Medical and Poisonous Plants of Southern and Eastern Africa" Second Edition, Livingstone, (1962).


Contributed by:

Roy Osborne (from Palms & Cycads, No. 7 April-June, 1985).

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