When it rains conkers

In one of the most popular scenes in the BBC adaptation of Jane Austen’s Pride and Prejudice [1], Mr Darcy (Colin Firth) dived into the lake at Pemberley and then encountered Elizabeth Bennet (Jennifer Ehle) while walking back to the house. His swim was an invention, although the meeting at Pemberley does take place in the book, as does the introduction to Mr and Mrs Gardiner (Tim Wylton and Joanna David). In that dialogue, there is further invention when Mr Darcy relates that he used to run from Pemberley into Lambton (more than four miles!) as a boy to collect horse chestnuts from the tree on the green. It did seem an odd thing to do, but maybe there were no suitable horse chestnut trees on the Pemberley estate, despite its many acres of “some of the finest woods in the country” [1]?

The dialogue brought fond memories of playing conkers to all of us who watched the programme: collecting the conkers; making a hole through the “best” ones with a meat skewer; and threading through a piece of strong and knotting its end. Then heading for the playground to try and demolish someone else’s conker by swiping at it with one’s own prized weapon, while avoiding, as much as possible, sore knuckles from an opponent’s misguided shot. During these contests there was much chat of how to prepare the best conkers (with vinegar and baking), although the ones we used were not treated.

I was reminded of those times earlier this week as I walked across Boxmoor in Hertfordshire, that has a splendid avenue of horse chestnut (Aeschylus hippocastanum) trees (see above). It had been raining and there was a moderate breeze, with the result that conkers were falling constantly and I was grateful that my bald head was covered by a cloth cap (although none of them fell on me). There were conkers all over the path and the freshly-fallen ones had that lovely lustre of polished veneers that soon dies on exposure to the air. Each conker is different in shape and patterning and they are beautiful: they provide yet another aspect of the “mellow fruitfulness” of autumn and one which brings, for me, a child-like appreciation of the natural world.

Christian believers might suggest that this is something that God intended at the time of the Creation, but atheists are more likely to point to the evolution of the horse chestnut, that began many millions of years ago, way before the creatures that led to H. sapiens first appeared. Conkers are, of course the means of dispersal of future generations of trees and we probably all remember planting some in pots and watching shoots appear at the surface of the soil.

Earlier this year, an interesting paper on the horse chestnut appeared in the Journal of Ecology [2]. It is a comprehensive account, well worth reading for those who love these trees, and it includes the following information:

Aeschylus hippocastanum is native to the Balkan Peninsula in south-east Europe but has been widely planted in temperate areas from the 17th Century onwards..

..Horse chestnut is best known as a tree planted for ornamentation and shade in parks and streets, particularly by the Victorians, since little else can rival the sight of a horse-chestnut in full flower. Indeed, it was voted the UK’s favourite tree in 2017 in a poll run by the Royal Society of Biology. The British population is an estimated 470,000 trees.

Like many other trees, horse chestnuts are attacked by insects and by disease organisms [2]. Those having the greatest aesthetic impact are larvae of a leaf-mining moth, Cameraria ohridella, that first appeared in the late 1970s in Macedonia. They feed on the tissue inside the leaf and produce unsightly brown blotches that have the effect of colouring the whole tree through the summer months and into autumn. While these attacks reduce the ability of the tree to photosynthesise, and thus produce energy, the trees still produce conkers (if smaller and in lower numbers than in unaffected areas). It would be so sad if future generations were prevented from enjoying the appearance of these wonderful fruits, then gathering them for a game of conkers. Or is that the sentiment of an old man, out of touch with the modern age?

[1] Jane Austen (1813) Pride and Prejudice. London, T.Egerton.

[2] Peter A. Thomas, Omar Alhamd, Grzegorz Iszkulo, Monika Dering and Tarek A. Mukassabi (2019) Biological Flora of the British Isles: Aeschylus hippocastanum. Journal of Ecology 107:992-1030.

The best coffee?

Like many people, I enjoy drinking coffee. My preference is for lightly roasted beans and I don't mind whether the coffee is made using a French press, a filter, or a commercial coffee machine. 

World-wide demand is such that many countries now produce coffee beans and the resultant crops vary in quality, depending on whether they are grown at altitude, as an understory in forests, in intensive plantations, or by other farming methods. Coffea arabica, the most widespread coffee plant, comes originally from north-east Africa and its global spread has brought problems, with much effort being given to controlling coffee borer beetles and other pests. Spraying of the crop is sometimes needed as there is often no natural biological control of the pests, and monoculture provides optimal conditions for pest transmission.

Ripe "cherries" are red, those that are over-ripe are dull brown-red and those that are yet to ripen are green (see above), so hand picking is often the best method of collection. The bean that we roast is contained within the cherry and, in the picture below, a cherry has been halved and the two beans it contains partly removed. The pulp and mucilage that surrounds each are obvious, as is the white parchment-like coating of the bean itself.

Coffee beans only develop their flavour upon roasting so they must first be extracted from the cherry.  As in many fruits, the soft pulp evolved to protect the bean (seed) from drying, or abrasion, and the mucilage layer provides an extra barrier that also allows easy penetration of the shoot when the seed germinates. Mucilage has many functions in Nature [1] and the layer is important in allowing the production of the famous Kopi Luwak from Indonesia [2]:

Although Kopi Luwak.. ..comes from the Indonesian islands of Java, Sumatra and Sulawesi, it is not its exotic location of origins but rather its unusual and quite unexpected method of production which contribute to its mystique and price. The desire to consume unique food products is a characteristic of passionate coffee drinkers.

So, what is the method of production of Kopi Luwak? The skin and pulp of ripe coffee cherries are naturally sweet and are thus attractive as foods for a number of vertebrates. Among these, the African civet feeds on coffee cherries in north-east Africa, the original home of the plant, utilising the pulp and then depositing the beans, protected largely by the mucilaginous coat, in their faeces. This passage is the basis of the production of Kopi Luwak, and begins with the collection of faeces of palm civets (below, upper) that climb trees and eat the beans in situ. They would originally have fed upon the many other forms of fruit available, but the arrival of coffee plantations provided a new, and concentrated, source of food. Coffee beans are retrieved from the palm civet faeces (below, lower) and are then washed and prepared for export. The collection of faeces from the wild has now been superseded by a battery-farming approach [3], with caged civets being fed coffee cherries, but the beans that have passed through civets are still a very tiny part of the total market for coffee beans. The same is true of coffee beans that pass through Jacu birds [4], that rival the fame of Kopi Luwak.

Ingestion of fruits results in the dispersal of seeds, but there are many other methods for this essential process that are more familiar to us:

- Coconuts falling into the sea and being carried large distances to other islands

- The winged seeds of sycamore that we used as "helicopters" when we were children

- The "clocks" of dandelions, with each seed having a parachute

- The explosive pods of gorse that fling seeds large distances

- Seeds of avens with hooks that attach to animal fur

These are just a few examples of a large number of dispersal mechanisms that have evolved and all readers will know of others. However, the passage of seeds through animal guts is less familiar to us, yet we eat many berries and pay little attention to what happens to the seeds they contain. The purple droppings that result from birds eating blackberries, elderberries and other fruits are more familiar, especially to car owners in late summer, but we are less aware that the droppings often contain seeds and that these are deposited in fertiliser, far from the parent plant.

Anna Traveset has reviewed the effect of frugivores (birds, non-flying mammals, bats, reptiles, fishes) on the germination of seeds that pass through the gut of animals and concludes [5]:

In addition to moving seeds from the parent plant to sites that can be suitable for recruitment and seedling growth, frugivore seed dispersers have the capacity to modify the germination patterns of many plants by varying the potential germinability of seeds, the rate of germination, or both.

The effect on germination is complex and depends on many factors, varying also from individual to individual. Each plant is likely to produce many seeds, so the main beneficial effect of having fleshy fruits is dispersal, just as it is for the other mechanisms listed above. All worth thinking about when eating strawberries, or when savouring a cup of Kopi Luwak, This unusual coffee is yet another example of the extraordinary power of evolution and of the ingenuity of humans in taking advantage of natural processes. Is it the best coffee though?

[1] http://rwotton.blogspot.co.uk/2015/08/we-cant-exist-without-slime.html

[2] Massimo F. Marcone (2004) Composition and properties of Indonesian palm civet coffee (Kopi Luwak) and Ethiopian civet coffee. Food Research International 37: 901-912.

[3] https://www.theguardian.com/lifeandstyle/wordofmouth/2013/sep/13/civet-coffee-cut-the-crap

[4] http://modernfarmer.com/2013/10/flight-jacu-bird/

[5] Anna Traveset (1998) Effect of seed passage through vertebrate frugivores' guts on germination: a review. Perspectives in Plant Ecology, Evolution and Systematics 1/2: 151-190.

Garden plants, seeds and being unnatural

Flowering plants produce seeds and these are dispersed away from the parent plant, many mechanisms having evolved for this purpose. These mechanisms range from winged seeds, to those with parachutes, plants having “pepperpots” to scatter seeds, to those that use explosive discharge. Wide-ranging dispersal is achieved after attachment to, or ingestion by, animals, and seeds may also be carried very long distances by wind and water. Providing conditions in newly-colonised regions are suitable for development, plants are then able slowly to increase their range. With changes in climate, and the movement of continents, through geological time, flowering plants have been very successful in colonising almost all terrestrial habitats and even some aquatic ones. This success is not the result of dispersal ability alone, but also of mutations in their genetic structure, resulting in adaptations of both structure and physiology. As a result, flowering plants are found in deserts, on mountains and in high latitudes as well as the profusion of types we find in temperate and tropical regions.

When early humans began to cultivate some of the wild plants around them, they began to select those that could be bred to produce crop plants, this being accompanied by a reduction in diversity, as the natural community was managed by our farming practices. Yet further along in human evolution, when we started having plants for decoration, even more selective breeding was undertaken and, as humans began to migrate, it was possible to take the seeds of plants that we liked, or needed, with us. That is the background to the work of botanical collectors who, for centuries, journeyed to find new wild plants in distant countries and then bring their seeds back for cultivation. The extent of such deliberate imports is unique to the activities of humans; no other organisms do this.

Many gardeners are familiar with the huge array of types of garden flowering plants that are available (and we not only propagate from seeds), but less familiar with their origins. Below are some suggested plants for borders given by Anna Pavord, the excellent writer on gardening [1]; the types of borders (Anna Pavord’s headings) being for gardens in temperate Europe. The scientific names of plants are given, together with their common names and varieties (the latter resulting from selective breeding by horticulturalists) and the original geographical locations of the parent plants [2]:

Cottage-garden border

Viola labradorica (Purple-leaved violet) - North America, Greenland

Bellis perennis (Double daisy) - Europe, Turkey

Camassia leichtlinii (Quamash) - North America

Aquilegia vulgaris (Columbine) - Europe

Daphne x burkwoodii - Europe, North Africa, Asia

Geranium pratense (Meadow cranesbill) - Europe, Central Asia, China

Paeonia Sarah Bernhardt (Peony) - Europe, Asia, North America

Salvia sclarea (Vatican sage) - Europe, Central Asia

Thalictrum delavayi (Meadow rue) - Western China

Campanula lactiflora (Milky bellflower) - Caucasus, Turkey

Gypsophila paniculata (Baby’s breath) - Europe

Lychnis coronaria (Rose campion) - Europe

Of these twelve plants, eight (67%) have European origins and one further has a wide distribution with many European relatives. A characteristic of cottage gardens is their “naturalness” and the recommendations above contain cultivars of wild flowers likely to be found in close proximity to the garden, cottages being characteristic of the countryside - at least, that is the image to be created. The planting is boosted by the appearance of plants that are not part of the natural flora of Europe.

A scheme for scent

Lilium candidum (Madonna lily) - Europe

Narcissus jonquilla (Jonquil) - Spain

Thymus x citriodorus (Lemon thyme) - Garden origin

Lavandula angustifolia (Lavender) - Mediterranean

Rosmarinus officinalis (Rosemary) - Mediterranean

Pelargonium Mabel Grey - ?South Africa

Iris graminea - Spain to Russia + Caucasus

Dianthus Prudence (Pink) - Europe, Asia, South Africa

Thymus serpyllum (Wild thyme) - Europe

Hemerocallis citrina (Daylily) - China

Daphne odora - China, Japan

There are eleven plants in this list, with seven (64%) that originate in Europe. In two cases (Pelargonium and Dianthus), the origins are vague as the possible parental stocks have a worldwide distribution.

A tropical summer border

Ensete ventricosum (Banana palm) - Ethiopia to Angola

Cleome hassleriana (Spider flower) - Southern South America

Canna indica (Indian shot plant) - South America

Argyranthemum frutescens - Canary Islands

Pelargonium Royal Oak - ?South Africa

Aeonium arboretum - Morocco

Felicia amelloides (Blue daisy) - South Africa

Cosmos Sensation - Mexico

Nicotiana sylvestris (Tobacco plant) - Argentina

Ricinus communis (Castor oil plant) - North Africa to West Asia

Given that the intention is to create a tropical summer border, it is no surprise that none of the plants originate in Europe and, indeed, many can only be grown outdoors during summer, as they cannot tolerate cold temperatures. This is another feature of the power of humans in gardening - we not only use transplantation of species, but choose where, and when, to locate them. There is a wide geographical spread of origins, including one representative found solely on an island chain.

A bold desert bed

Datura (Brugmansia) x candida (Angels’ trumpets) - Garden origin

Gazania uniflora - Tropical Africa

Agave Americana - Mexico

Fuchsia Thalia - Central and South America

Begonia rex (King begonia) - Himalayas

Phormium tenax (New Zealand flax) - New Zealand

Aeonium arboretum - Morocco

Kniphofia caulescens (Red hot poker) - South Africa

Eucalytus niphophila (Alpine snow gum) - Australia

Crassula falcata (Aeroplane propeller) - South Africa

Echeveria gibbiflora - Mexico

Yucca whipplei (Our Lord’s candle) - USA, North Mexico

As would be expected, there are no representatives from Europe in this list and the geographic spread is even wider than for the tropical summer border. It is worth pointing out that some desert plants cannot be grown outdoors in most of Northern Europe and fanciers of cacti and some succulents will need heated greenhouses for their collections. This is an example not only of human ability to transplant, but also to change the environment in which the imported plants grow.

Although a very large number of plants have been collected for gardens, some have escaped and invaded surrounding areas, mingling with the native flora. This represents a reverse of the position of weeds (wild, native plants) in gardens and, while many of the invaders from gardens provide an excellent “show”, some have habits which mean that they become a nuisance, sometimes dominating, and excluding, local plants that would not have to compete under natural conditions with these very recent invaders. There are many examples and I’ll just mention three.

Hedychium gardnerianum (Kahili Ginger - below, top) is native to the Himalayas and is a striking plant which has been imported both for its foliage and for its scented spikes. It produces sticky seeds that aid dispersal in its natural habitat and these also provide one of the means that encourage its spread elsewhere. It has become a serious invasive pest in several areas of the world and, once present, is difficult to remove. The same can also be said of my other two examples: Impatiens glandulifera (Himalayan Balsam - below, middle) and Fallopia japonica (Japanese Knotweed, below, bottom). As its common name suggests, I. glandulifera is, like H. gardnerianum, a native of the Himalayas and shares the same high dispersal ability. The balsam has attractive pink flowers which appeal to gardeners, and its success in dispersal results from the explosive release of seeds that scatter from the parent plant. As riparian zones of streams and rivers are especially favoured by these invading plants, the flowing water provides another excellent means of dispersal, as the seeds are carried downstream after being shot out.

F. japonica colonises many habitats.  A hollow-stemmed plant, it shows rapid growth and produces many leaves, giving effective ground cover and, with its height, a means of hiding unattractive or derelict areas. Vegetative growth by means of rhizomes ensures that there is strong lateral spread and only a small section of rhizome is needed for the successful growth of a new plant, the rhizomes possessing such strength that they can cause damage to buildings and any solid structures with which they come in contact. Once established, Japanese Knotweed is very difficult to kill and it is such an effective plant that special operatives may be necessary to remove it.

The collection of seeds from plants that grow in very distant regions, and then bringing them to countries that are highly unlikely to be colonised naturally, is a means of dispersal that is markedly unnatural. It should therefore not surprise us when some plants - and animals - "escape" and reach pest levels. They have been transplanted from the regions where they evolved over millions of years and where they are part of different, complex communities that contain natural controls.  It is another result of humans needing to modify Nature, rather than feeling part of it.

[1] Anna Pavord (1994) The Border Book. London, Dorling Kindersley.

[2] Christopher Brickell [Editor-in-Chief] (1996) The Royal Horticultural Society A-Z Encyclopedia of Garden Plants. London, Dorling Kindersley.

Elders and brambles: foods and mythologies

It is early summer in Great Britain and many hedgerows are dominated by the creamy blossoms of the elder. Last week, I picked some, cut the flowers from the stems and steeped them, together with slices of lemon, in sugar solution to make elderflower cordial. ¹ It is such a simple thing to do, but the end product is delicious, whether taken diluted with water, or with some fizzy wine. Some would argue that it is much easier to buy a bottle in a store, as elderflower cordial is now available so readily, but there is something satisfying about producing one’s own and, like all those who do, I think my cordial tastes better than commercial brands.

I’ve always liked collecting food from the countryside and there are many opportunities, especially in late summer and autumn. Elderberries then ripen and can be collected to make jellies ² (do try it, if you’ve not already done so) and there is an abundant supply of blackberries. Indeed, it puzzles me that there are punnets of blackberries on sale in supermarkets at the time there are masses of the same fruit in hedgerows, although I admit there is a price in their collection, as one rarely escapes without a few scratches from thorns while gathering berries.

One of the reasons that few of us pick berries is that we are very far from our hunter-gatherer roots and have little knowledge of which wild foods are edible and which are not. Our ancestors, who had received this information from older people around them, collected wild fruits much more readily and they were also aware of mythologies that surround the plants on which they grow. In Great Britain, brambles and elders are both associated with superstitions and it must be borne in mind that both stain red, an association with the colour of blood. Anyone passing through a bramble arch (formed where a branch has grown out and rooted on touching the ground) was thought likely to be cured of a number of medical complaints, amongst which was whooping cough. ³ Children unfortunate enough to be infected with Bordetella pertussis (the bacterium which causes whooping cough) therefore felt miserable from all the coughing and also sore from scratches provided by the bramble. Perhaps it formed a distraction? Scratches from the arch are likely to be beneficial in the cure of other illnesses and drawing of blood has been regarded as an excellent way of treating infections in the recent past (see any description of the use of lancets, or leeches).

Elder has a much more complex role in superstition and mythology. As Steve Roud explains: ³

“Elders were everywhere connected with fairies and witches, although it was not always clear in what way. It was also reputed to be the tree on which Judas Iscariot hanged himself, and it was believed to have provided the wood for the Crucifixion. Furthermore, it must never be cut down, or the wood burned; it must never be used to make cradles; a wound inflicted with an elder spike was bound to prove fatal; and the tree would ‘bleed’ if cut.

It has proved impossible to reach an adequate synthesis of elder beliefs, because the evidence is patchy and contradictory, and all that can be said is that elder was generally agreed to be ‘uncanny’. There is a curious sense that the negative and positive feelings stemmed from the same basic notions and may have depended largely on the general disposition of the informant.”

We know that humans are imaginative in providing explanations and this shows well when we consider old superstitions. The power of our imagination is also important in affording religious explanations. For example, the abundance of berries is late summer and autumn is understood by some Creationists as being a gift from God, being a loose interpretation from the text in Genesis in The Holy Bible: ⁴

“And God said, Let the earth bring forth grass, the herb yielding seed, and the fruit tree yielding fruit after his kind, whose seed is in itself, upon the earth: and it was so. And the earth brought forth grass, and herb yielding seed after his kind, and the tree yielding fruit, whose seed was in itself, after his kind: and God saw that it was good.”

The implication here is that God created fruit trees and that they were “good”, meaning that fruit had been supplied for human consumption.

However, the production of fruits has been a feature of the biology of these plants long before humans appeared. Blackberries and elderberries contain the seeds that germinate to give the next generation of plants and these seeds must be dispersed. Some fruits will fall near the parent plant and be in competition with it, but others will be eaten by birds and other animals, attracted by their colour and succulence. Seeds pass through the gut of these grazers and are deposited in faecal matter, usually at some distance from the parent plant. The seeds are thus dispersed and also start to grow in a little patch of concentrated nutrients. The cost to the parent plant is the production of an excess of fruits to ensure that the process of dispersal is optimal and this strategy has developed through evolution. My picking of berries, or flower heads, is taking advantage of this natural trend. Of course, some would argue that this was all part of the Creation........

¹ http://www.bbc.co.uk/food/recipes/elderflowercordial_6465

² http://www.waitrose.com/home/recipes/recipe_directory/e/elderberry_jelly.html

³ Steve Roud (2003) The Penguin Guide to the Superstitions of Britain and Ireland. London, Penguin Books.

⁴ Genesis Chapter 1 verses 11-12. The Holy Bible (Standard King James’ Version).