Tuesday, 23 August 2016

Bird of Paradise Flowers

The striking flower arrangement shown above is by Jane Hass and features two blooms of Strelitzia reginae, commonly known as the Bird of Paradise Plant, or the Crane Flower. These names were given to the plants because they reminded some observers of the two birds, but only an avid Creationist would believe in such mimicry, or that they were devised for our visual pleasure. S. reginae is native to South Africa, where it grows on river banks and in woodland clearings, and it was so attractive to collectors that seeds have been exported widely and the plant grows well in warm climates. It is the official flower of the City of Los Angeles [1].

Each flower consists of bright orange sepals and darker petals and these emerge from a spathe (the pointy section that looks like the beak of the bird in our imagination). At the base of the petals is a nectary containing sugars that change in their composition over time [2], although we do not know the reason for this.

Nectar is produced by almost all flowering plants and provides an attractant for animals that use it as an energy source and then collect pollen that is transferred to another plant to ensure fertilisation. Most commonly, the pollinators are insects and the plant loses sugars (produced abundantly during photosynthesis), and some of the pollen (many bees collect this, for example), but the mutualism between the plant and the pollinating insects is clearly of benefit to both and is a very successful strategy. Insects are not the only pollinators, however, and S. reginae is fertilised by birds, with its pollen formed into threads and aggregates [3] to enhance attachment and transmission. The most common pollinator is the Cape Weaver (Ploceus capensis – see below), that feeds on the pollen aggregates as well as the nectar and transfers pollen on its feet while visiting another flower [4,5], with the rigid spathe providing an ideal initial landing place. 

Visits by weaver birds have described by Hoffman et al. [6]:

Landing of the bird on the blue sheath-forming petals exposes the hidden pollen to the feet of the bird, while the bird probes the corolla tube with its beak and extends its tongue to reach the nectar.. .. Once landed and feeding, these birds have been observed to seldom move their feet, thus keeping self-pollination low.. .. As a consequence, the best place for the bird to feed is also the best position for pollination.

Sunbirds (Cinnyris spp.) also visit S. reginae plants, but it is likely that they play little part in pollination and they are regarded as "nectar thieves" [5]. As Coombs and Peter note [7]:

The nectary of S. reginae is covered by the convoluted bases of the two fused petals forming a barrier to the opening of the corolla tube.. ..The behaviour of sunbirds indicates that they are nectar thieves and can manipulate the nectar barrier with their beaks to gain access to the nectar without causing obvious damage to the flowers of S. reginae.

Pollination in S. reginae is thus an example of the evolution of a strategy that depends on mutualism, with other species taking advantage of the "gifts" provided by the plant. 

So what happens when seeds are taken to other countries? An abundance of imported seeds ensures that plants can be grown without the need for fertilisation, but we now know that S. reginae is pollinated by indigenous birds. The common yellowthroat of southern North America (Geothlypis trichas – see below), a type of warbler, feeds on nectar and, just as with the weaver birds in Africa, picks up pollen on its feet. As Hoffman et al. point out [6] it is unlikely that "adaptive floral changes have started the association" in the very short time during which S. reginae have been grown in the USA, but the behaviour of the warblers allowed them to discover the nectaries and release pollen on to their feet and thus ensure fertilisation. All this mimicking an association that evolved over very long time periods in South Africa where the plant is endemic.

It is interesting to speculate on how yellowthroats developed this behaviour. The bright sepals of S. reginae may be an attractant to many animals, including the insects and other invertebrates on which the warbler feeds. Could it be that the habit of feeding on nectar, and picking up pollen on the feet, happened through successive visits of some birds to feed on insects; a behaviour that became established in populations as a result of learning from other individuals? Whatever its origins, it is another example of the wonder of evolution and of Natural History.


[2] Eva C. Kronestedt-Robards, Maria Greger and Anthony W. Robards (1989) The nectar of the Strelitzia reginae flower. Physiologia Plantarum 77: 341-346.

[3] ] Eva Kronestedt-Robards (1996) Formation of the pollen-aggregating threads in Strelitzia reginae. Annals of Botany 77: 243-250.

[4] Adrian J. F. K. Craig (2014) Nectar feeding by weavers (Ploceidae) and their role as pollinators. Ostrich 84: 25-30.

[5] G. Coombs, S. Mitchell and C. Peter (2007) Pollen as a reward for birds. The unique case of weaver bird pollination in Strelitzia reginae. South African Journal of Botany 73: 283.

[6] F. Hoffmann, F. Daniel, A. Fortier and S.-S. Hoffmann-Tsay (2011) Efficient pollination of Strelitzia reginae outside of South Africa. South African Journal of Botany 77: 503-505

[7] G. Coombs and C. I. Peter (2009) Do floral traits of Strelitzia reginae limit nectar theft by sunbirds? South African Journal of Botany 75: 751-756

Wednesday, 10 August 2016

Crocosmia, invasion, diabetes and obesity

The rich flora of southern Africa has provided us with many garden plants, including members of the iris family that naturalise readily [1]. Among the most popular of these plants is montbretia, or coppertips (Crocosmia x crocosmiiflora – a cross of C. aurea and C. pottsii [2]), the result of horticultural inter-breeding and now popular world-wide for its attractive foliage and, especially, its orange-red flowers.

Montbretia has two methods of reproduction: fertilisation of the flowers by insects (and, in some closely-related Crocosmia plants, by wind or humming birds) to produce seeds; and vegetative reproduction, where each plant produces stolons, or runners, that form new plants when roots and leaves grow from nodes.

Flowering occurs over a period of days, with the first flowers at the base of the spike and then sequentially towards the tip, the production of seeds following the same sequence. This habit ensures that some flowers are likely to be fertilised during optimal conditions for pollination, and the seeds, similarly, are produced over time to ensure that dispersal is optimal. This flowering habit is a feature of many plants, but it is important to recognise that it evolved to the advantage of the plant a very long time before humans appeared. It was not designed by, and for, gardeners.

Vegetative growth by stolons ensures local colonisation and many gardeners like to divide dense clumps, as they tend to choke off other plants (a measure of the success of the strategy). Each individual montbretia grows from a corm and this develops after the successful germination of seeds and the growth of the first colonising plant. It is likely that the casual disposal of corms, rather than the spread of seeds, allowed montbretia (coppertips) to be such a successful coloniser of natural habitats, frequently forming large and vivid clumps on embankments and in coastal regions [2]. When established, its growth habit ensures its spread and it may now be regarded by some as a "wild flower".

Each corm is a store of starch grains produced synthetically after photosynthesis and this store allows the growth of leaves and stems at the beginning of the growing season. It is also used in shorter time scales to allow the efficient metabolism of the plant. Starch grains that are stored by plants for months often have their surface eroded [3], resulting from the action of naturally-occurring enzymes involved in releasing easily-metabolised sugars from the more complex starch. Among these is α–amylase and this enzyme is disabled in montbretia corms by the presence of a compound called montbretin. This ensures that starch grains are retained in good condition during resting phases, montbretin being of less significance when starch is being metabolised.

The presence of montbretin, the metabolism of the plant, the succession of flowers and seeds, and the vegetative spread by stolons, are all extraordinary adaptations that make montbretia such a successful plant and an effective invader. In addition, montbretia has recently received attention in the world human health, something which always results in wide publicity. It has been discovered that montbretin not only serves to protect starch grains from the action of α–amylase in Crocosmia corms, but may also inhibit the action of these enzymes in humans, something that offers the possibility of new drug treatments against diabetes [4]:

Type 2 diabetes mellitus is a condition that affects well over 320 million people worldwide and is closely associated with obesity. Among the oral antidiabetic drugs used for its treatment are the α-glucosidase inhibitors, which prevent hyperglycosemia by slowing digestion of starch and malto-oligosaccharides in the gut. Partial hydrolysis of starch is accomplished by salivary α-amylase, with principal cleavage provided by human pancreatic α-amylase (HPA) within the gut, generating linear and branched malto-oligosaccharides. These in turn are broken down to glucose by α-glucosidases that are anchored in the epithelium of the small intestine..

..Selective inhibition targeted at only HPA, the enzyme at the top of the starch digestion pyramid, could be used to quantitatively modulate blood glucose levels by restricting or even shutting down starch degradation, thereby minimizing the specificity problems that arise with currently available α-glucosidase inhibitors.

This is written in the technical language of a scientific paper, but Williams, Zhang et al. [4] then describe the selective nature of montbretin A (MbA) and its possible value in medicine:

Because MbA is such a potent inhibitor and is easily isolated from the corms of a readily grown plant (Crocosmia sp.), it has potential as a new agent for controlling blood glucose levels in diabetics and obese patients. 

So, the mechanism that evolved in Crocosmia to conserve starch grains is one in which the pharmaceutical industry is likely to show a great deal of interest, given the numbers of diabetics and the "epidemic" of obesity in many countries. This medical application could lead more people to think about the evolution of Crocosmia and its Natural History, helping us to move away from our dominant anthropocentric view and towards a sense of wonder in the capabilities of all living organisms. 

Well, it should do.

[1] Mark Van Kleunen, Steven D. Johnson and Markus Fischer (2007) Predicting naturalization of southern African Iridaceae in other regions. Journal of Applied Ecology 44: 594-603.

[3] A. T Modi and R. Mare (2016) Alpha amylase activity and sprouting during short term storage of taro corms. Journal of Agricultural Science and Technology 18: 1053-1063.

[4] Leslie K. Williams, Xiaohua Zhang + 11 authors (2015) The amylase inhibitor montbretin A reveals a new glycosidase inhibition motif. Nature Chemical Biology: published online 27th July 2015 DOI 10.1038/NCHEMBIO.1865.

Tuesday, 2 August 2016

"The Narcotics We Indulge In" – a view from the 1850s

On a recent visit to Scotney Castle, I discovered a copy of James Johnston's The Chemistry of Common Life among the many books in the Library [1]. It is an interesting book that gives descriptions of the physiology of organisms and has several sections on narcotics and their use by humans. Johnston had written on this topic earlier and his two articles published in August and November 1853 in Blackwood's Edinburgh Magazine were re-printed in the Journal of Psychoactive Drugs in 1985 and 1986 [2,3]. He gives us insights into the worldwide use of narcotics up to the 1850s.

Johnson was a Scot who graduated in Philosophy from the University of Glasgow and then pursued a school teaching career in Durham from 1825 to1830 [4]. Having made a successful marriage, he was able to leave teaching and pursue his interest in Chemistry, including studying with Berzelius in Sweden, and this resulted in his being appointed the foundation Reader in Chemistry and Mineralogy at the University of Durham [4]. It was in the field of Agricultural Chemistry that he was best known and his research work was recognised by Fellowship of the Royal Society in 1837 [5]. In the Oxford Dictionary of National Biography, Knight writes that:

Johnston became a successful popular lecturer and writer.. ..His Chemistry of Common Life.. ..was a classic popularization of up-to-date science.

Chapters in The Chemistry of Common Life [6] on the fermentation of alcohol, and its subsequent distillation, are followed by a section on "The Narcotics We Indulge In" (based on the articles in Blackwood's Edinburgh Magazine). Johnston provides a wide-ranging review of the world-wide use of "narcotic indulgences", the most important of which are mentioned in his concluding comments:

Siberia has its fungus [Amanita muscaria] – Turkey, India , and China, their opium – Persia, India, and Turkey, with all Africa, from Morocco to the Cape of Good Hope, and even the Indians of Brazil, have their hemp and haschisch – India, China and the Eastern Archipelago their betel-nut and betel-pepper – The Polynesia islands their daily ava [from the ground roots of Piper methysticum] – Peru and Bolivia their long-used coca – New Granada and the Himalayas their red and common thorn-apples [Datura sanguinea and D. stramonium] – Asia and America, and all the world, we may say, their tobacco – the Florida Indians their emetic holly [Ilex vomitoria] – Northern Europe and America their ledums and sweet gale – the Englishman and German their hop, and the Frenchman his lettuce.

All these narcotics come from fungi or plants and most are familiar to us, perhaps with the exception of the use of lettuce; the sap of some types of lettuce being dried and powdered and used in a similar way, and with similar properties, to opium. Johnston describes tobacco as being consumed world-wide in the 1850s, either smoked or taken as snuff, and other narcotics were widely available: laudanum, for example, consisted of 10% powdered opium in 20 – 50% alcohol and was used as a painkiller and cough medicine, some writers and artists also taking it for the effect on their powers of creativity. The main psychoactive constituent of opium is morphine and it was known to be addictive – Coleridge was a well-known addict whose difficulties are described by Johnston.

"The Narcotics We Indulge In" concludes with a summary that adopts a high moral tone, as befits someone from the Scottish Kirk tradition:

..there exists a universal craving in the whole human race for indulgences of a narcotic kind. This is founded in the nature of man.. ..this craving assumes in every country a form which is more or less special to that country. It is modified most by climate, less by race, and least, though still very sensibly, by opportunity.. ..among every people the form of craving special to the whole undergoes subsidiary modifications among individuals. These are determined by individual constitution first, and next by opportunity..

..I may remark that, with the enticing descriptions before him, which the history of these narcotics presents, we cannot wonder that man, whose constant search on earth is after happiness, and who, too often disappointed here, hopes and longs, and strives to fit himself for happiness hereafter – we cannot wonder that he should at times be caught by the tinselly glare of this corporeal felicity, and should yield himself to habits which, though exquisitely delightful at first, lead him finally both to torture of body and to misery of mind; - that, debilitated by the excesses to which it provokes, he should sink more and more under the influence of a mere drug, and become at last a slave to its tempting seductions. We are indeed feeble creatures, and small in bodily strength, when a grain of haschisch can conquer, or a few drops of laudanum lay us prostrate; but how much weaker in  mind when, knowing the evils they lead us to, we are unable to resist the fascinating temptations of these insidious drugs!

Although Johnston admits that the use of tobacco and opiates had become global in the 1850s, he would probably have been surprised at the widespread use of drugs that is prevalent today and the various forms that they take. Clearly one difference is the development of synthetic drugs like LSD and amphetamines that are produced in chemical laboratories, rather than directly from fungi or plants. One aspect that would not have surprised him is the money involved in the production and selling of narcotics, as he remarks on the world-wide size of this industry in The Chemistry of Common Life.

The widespread use of "narcotic indulgences" for religious purposes affects whole societies, but why do some of us become addicted to narcotics, knowing that they can be destructive to physical and mental health? It is hard not to adopt Johnston's position when addressing this question, as we experiment with drugs, feel pressured by peers, want to enhance our creativity, escape boredom, or indulge for many other reasons. Apart from the change in the range of narcotics available, there are few differences between the 1850s and the 21st Century in our need for what we now call recreational drugs. Does that come as a surprise?


[2] James F. W. Johnston (1985) The narcotics we indulge in. Part I. Journal of Psychoactive Drugs 17: 191-199.

[3] James F. W. Johnston (1985) The narcotics we indulge in. Part II. Journal of Psychoactive Drugs 18: 131-150.

[4] Graeme Wynn (1985) Johnston, James Finlay Weir. Dictionary of Canadian Biography Volume 8. Toronto and Québec, University of Toronto and Université Laval.

[5] David Knight (2004) Johnston, James Finlay Weir (1796-1855). Oxford Dictionary of National Biography. Oxford, Oxford University Press

[6] James F. W. Johnston (1854) The Chemistry of Common Life. New York, D. Appleton and Company.