A Digital Botanic Garden

Fairchild's Mule...... almost

2012-01-16T21:28:00.004Z

Thomas Fairchild (1667-1729) was a nurseryman from Hoxton who is credited with producing the world's first deliberate man-made hybrid plant, when in 1717 he crossed a carnation (Dianthis caryophyllus) with sweet William (D. barbatus) to produce a sterile hybrid with intermediate characteristics. He presented a pressed specimen to the Royal Society and you can see an image of what I assume is the same herbarium specimen here.

Being a devout church-goer and believer in divine creation, Fairchild was perturbed by what he had done, which carried a whiff of blasphemy about it, and perhaps to atone left a bequest to his parish church (St.Leonards in Hackney Road) for an annual sermon on the 'wonderful works of God' which is still delivered annually, at Whitsun, to the Worshipful Company of Gardeners, decked out in their ceremonial gowns, although the venue is now St.Giles, Cripplegate. You can read more about Fairchild here , where there is also a photograph of his gravestone.

Fairchild's experiment was a landmark in plant science, ushering in an era of controlled hybridisation between plant species that has resulted in many of the garden plants that we now grow - and also many important crops. 'Mule', incidentally, as a term for a sterile interspecific hybrid, still persists in animal breeding circles. When I was a child my grandmother kept a goldfinch mule - a purported hybrid between a goldfinch and a canary that was supposed to sing better than either parent.

I've long been intrigued by Fairchild's mule and have often wondered whether one of the parents was indeed a carnation or perhaps might have been a garden pink D.plumarius, which was a popular plant in Fairchild's day, easier to grow, much appreciated for its carnation scent and often referred to in old gardening books and in popular parlance as a 'carnation'. Fairchild almost certainly grew pinks and it's hard to believe that he would not have tried making hybrids with those - especially as they bloom at the same time as sweet Williams.

Anyway, here's my attempt at producing a modern-day equivalent of Fairchild's mule, raised by crossing a garden pink Dianthus plumarius with sweet william D. barbatus, with the former as the female parent. Like Fairchild's mule it turned out to be sterile but was easy enough to propagate from cuttings. I tried to backcross it to both parents but couldn't produce any seed from either of those crosses.... presumably because the hybrid's pollen was sterile.

My mule was very tough little plant with wiry stems - very reminiscent of the herbarium specimen mentioned above and of published descriptions of the original hybrid. It was incredibly floriferous, with every hybrid I raised having the same magenta flowers, which didn't have much detectable scent. It flowered perpetually through the summer and I had difficulty in finding non-flowering shoots to root as cuttings. Eventually it literally flowered itself to death.

This year I'm planning to have a go at producing a proper Fairchild's mule using carnation rather than a pink as a parent, to see whether it resembles my earlier attempt using a pink. It requires much more effort to grow carnations than to grow pinks, though.

In 2000 Michael Leapman published a detailed account of Fairchild's life and work, entitled The Ingenious Mr. Fairchild: the Forgotten Father of the Flower Garden (Headline, ISBN 0747273596) - well worth reading if you can find a copy.

Solanum lycopersicum, Tomato, Solanaceae

2011-12-29T22:45:00.000Z

My mother always told us not to play with our food when we were kids but when you're a grown-up botanist you just can't help yourself: it's so interesting. I doubt whether zoologists get quite so much pleasure from this activity because animal food is usually dismembered and cooked to oblivion, whereas a lot of the plant food that we eat is more of less intact and open to easy investigation.

This slice of tomato, Solanum lycopersicum, eventually destined to be part of my BLT, shows the essential characteristics of the fruit, which is botanically a berry - defined as a fleshy fruit derived from a single ovary. In the tomato's case it's a multi-seeded berry, with each of the numerous individual seeds attached to the central placenta via its own vascular supply. You can see in this section that the fleshy fruit wall - the pericarp - is divided into distinct layers: the outer exocarp (with more concentrated red pigment); the mesocarp; and the endocarp which is partly juicy and fills the fruit chambers (loculi) that surround the seed.

It has all evolved to attract a hungry animal and those seeds in the fruit loculus are perfectly capable of passing through the mammalian gut unharmed. That's why feral tomato plants are often a prominent feature of sewage farms. Seeds of the distinctive yellow fruits of the Galapagos tomato, Solanum cheesmaniae, endemic to those islands, are eaten by Galapagos giant tortoises that disperse the seeds (slowly and not very far away) in their droppings.

Tomatoes are said to have been introduced into Europe by the Spanish conquistadors, who found that they were already widely cultivated by Mesoamerican civilisations when they arrived in the New World. For centuries tomatoes were viewed by Europeans with suspicion and considered to be poisonous. Somehow the idea that they were aphrodisiacs arose, first in Italy then in France and finally in England and they became known in all three languages as 'love apples'. The term persisted for a long time and in my copy of Everyman His Own Gardener:The Complete Gardener, written by Thomas Mawe and John Abercrombie and published in 1855 - and which you can download here - they are still referred to both as 'love apples' and tomatoes, although by that time their tasty flavour and nutritious qualities were recognised.

Modern cultivated tomatoes tend to be reliably self-pollinated, with their stigma hidden inside a ring of stamens that shed pollen directly onto its surface, but in wild species the stigma protrudes well beyond the end of the stamens and requires an insect to transfer pollen to it. This is the flower of a cultivated tomato, with the anthers just beginning to shed pollen onto the stigma hidden within.

Part of the pleasure associated with eating a tomato comes from the aroma, which is always far inferior in supermarket chiller-cabinet fruit to the sensory qualities of a warm, ripe tomato picked directly from a plant on a summer's afternoon. That alone makes them worth all the effort needed to grow them, even though it's more expensive to do so. I like the smell of the plants as well when you brush against them in the greenhouse and much of that emanates from the surface hairs, or trichomes, which cover most of the plant.

There are two kinds of trichomes on tomatoes - long, simple hairs and short glandular hairs whose heads of swollen cells are filled with aromatic compounds.

You can see both here, on a flower pedicel, with the very short glistening glandular hairs covering it's surface.

Here, at higher magnification, you can see just how densely packed they are. Some tomato genotypes have glandular trichomes that contain particularly high concentrations of insect-repellent volatiles, and there's now a lot of interest in transferring this characteristics to cultivated tomatoes, to reduce the need for growers to use chemical pesticides to tackle aphids, red spider and white fly, which can blight the life of an avid tomato grower.

Starfish Flower, Stapelia variegata, Apocynaceae

2011-12-13T17:00:00.000Z

Stapelia variegata belongs to a select group of plants with sapromyophilous flowers - flowers that mimic the scent (and sometimes colour and texture) of carrion, attracting fly pollinators that are deceived into laying eggs on them and accidentally pollinate the flowers as they do so. The odour of flowers with this pollination syndrome can vary - from mildly unpleasant (as in the case of S.variegata, where you need to be quite close to detect it) to truly nauseating (as in the case of Dracunculus vulgaris).

The surface of starfish flower feels like wrinkled flesh and those brown spots are rather similar to the early symptoms of putrification in a pale-fleshed corpse.The inner parts of the flower - known as the corona - are surrounded by a raised ring called the annulus and consist of five horizontal bifurcating segments and five bifurcating, upright horn-like structures, which together appear to guide wandering flies towards the functional reproductive organs, although it's not clear exactly how they do this. The male anthers on the inner corona lobes are in the form of a pollinium so are carried off in their entirety on the leg or proboscis of a visiting fly. The stigma is located within the outer corona lobes, which guide the pollinium attached to a visiting fly onto the stigma surface. You can read a plant breeder's account of Stapelia flower structure and pollination here.

Stapelia is a predominantly South Africa genus of succulent plants which used to be classified within the family Asclepiadaceae (milkweeds). This species is very easy to cultivate as long as it's planted in a well drained compost and not overwatered. This is also an easy species to raise from seed - which is worthwhile because the mottling on the flowers is quite variable - so amongst a batch of seedlings you might find something unusual and interesting.

California flannel bush, Fremontodendron californicum, Malvaceae

2011-11-29T18:23:00.000Z

Until the harsh winter of 2009-10 I had a 3m. tall specimen of this lovely Californian shrub growing in my back garden, but sadly the severity of that winter killed it and I haven't yet got around to planting another. It comes from the foothills of the Sierra Nevada, thriving in nutritionally poor soil - which explains why it did do well when it was rooted close to my leylandii hedge, in a very dry spot where nothing else will grow. It's also a good wall shrub, doing well in the rubble around the foundations of a house and trained against a south-facing wall.

The flowers are interesting because, like those of hellebores, the parts that look like petals are actually the sepals - there are no true petals.

It's a very prolific producer of nectar (you can see nectar drops glistening in the image above) so bumblebees love it.

You do need to be careful when you prune the plant though, because the densely hairy stems and leaves (which account for its name of flannel bush) can cause skin irritation. The cultivar that's most often sold in Britain is usually labelled California Glory.

The plant has traditionally been classified in the family Sterculiaceae, but modern phylogenic studies by the Angiosperm Phylogeny Group, based on DNA sequence data that gives a more accurate reflection of evolutionary relationships, place it in the mallow family - the Malvaceae. Gardeners, and sometimes even professional botanists, often deplore the way in which plant scientific names and classification change so often but they shouldn't - it reflects the fact that someone, somewhere is still taking an interest in the world's flora and that traditional taxonomic botany isn't totally moribund in universities.

Fremontodendron, also know under the synonym of Fremontia, was first discovered by General Fremont near Sacramento in 1846 and was named after him - you can read an account of the colourful life of this soldier, explorer, anti-slavery campaigner, politician and plant collector here.

Water hyacinth, Eichhornia crassipes, Pontederiaceae

2011-11-10T14:13:00.001Z

Water hyacinth Eichhornia crassipes is often rated as one of the world's top ten worst weeds, thanks to its prodigious capacity to spread over the surface of lakes and rivers. It's said that just one plant can multiply to cover an acre of lake surface in eight months, thanks to its ability to produce stolons that sprout new plants from their tips. While vegetative spread explains its local abundance, its short-lived but beautiful flowers have also played a part in its current worldwide distribution in the tropics. It comes from South America but is now a problem in Africa, India and the Far East where it has been introduced as an ornamental species that has quickly rampaged out of control. It carpets parts of Lake Victoria in Africa, impeding navigation, and within a year of being introduced onto the Sudanese Nile in 1957 it had spread along 620 miles of river.

Water hyacinth isn't hardy in Britain, although there were a couple of reports of it surviving outside through the winter in Norfolk a few years ago. The last two severe winters would certainly have killed any plants in garden ponds, but it does make an attractive plant for a conservatory. Here it's sharing its indoor pond with another notorious aquatic weed, water lettuce Pistia stratiotes, which is equally prolific.

Water hyacinth owes its buoyancy to these inflated leaf petioles. When you cut these open ...

... you find that they are sub-divided into hundreds of small, rectangular compartments with thin walls of papery cells.

Although water hyacinth is a problematic weed there's a lot of research going in into useful applications of this plant. These include bioremediation - using its capacity to absorb and sequester toxic metals like mercury, chrome, lead, cadmium, zinc and arsenic via its fibrous root system that dangles in the water. Numerous trials have been carried out for waste water treatment. It has also been used as animal feed (from plants grown on clean water) and there's extensive research into using its rapid biomass production as a source of energy, by using the harvested plants to produce biogas or bioethanol.

Rose grape, Medinilla magnifica, Melastomataceae

2011-11-02T23:11:00.003Z

Rose grape Medinilla magnifica is high on my lamentable list of 'plants that I wish I'd taken better care of'. I bought one in the spring, it flowered well through the summer, struggled through a winter in my cool conservatory, had a final flourish of flowering in the following spring then keeled over and died. But while it lasted it lived up to its specific name and was truely magnificent. It's an excellent plant for growing in a pot on a high shelf, so that you can look up and appreciate its spectacular dangling inflorescences.

Medinilla magnifica is native to the island of Luzon in the Philippines, where it often grows as a large epiphytic shrub on trees. I visited Luzon a couple of times about 25 years ago, without being lucky enough to see it flowering in its native habitat - but if I could afford a fully heated conservatory with supplementary lighting in winter, it would be first on my list of plants to acquire again.

The Melastomataceae is a tropical family - you can find more on another member of the family that's much easier to cultivate as a house plant here.

Wax plant, Hoya carnosa, Asclepiadaceae

2011-10-26T10:04:00.000+01:00

The flowers of Hoya carnosa, with their massive drops of glistening nectar, remind me of Man Ray's famous photographs of fake glass tears on a woman's face. They seem as surreal as his photographs - but are genuine enough; whenever I've grown this plant I've had to spend a lot of time cleaning off the black mould that tends to grow on leaves splashed with the sugary secretion. Apparently Victorians like to wear Hoya inflorescences in their coat buttonholes - presumably removing those sticky drops first.

Those petals are pretty extraordinary too - they look as though they're made of fake pink fur.

I've seen bees visiting H.carnosa in my conservatory but it's hard to find information on its natural pollinators in the wild. It seems likely that they are nocturnal moths because there are two published studies which show that there is a circadian rhythm of scent emission (1) and nectar secretion peaking at around midnight (2). Members of the Asclepiadaceae have an unusual pollination mechanism, where insects carry away the whole anthers, as a structure known as the pollinium, that attaches to them via an organ called a translator - similar to the pollination mechanism found in orchids. You can see sketches of Hoya pollinia here.

Those massive nectar droplets must be the moth's reward for its exertions.

Hoya carnosa seems to have a wide distribution in South East Asia but old gardening books I've consulted indicate that it was introduced to Britain from Queensland in 1802. It's named after Thomas Hoy, who was the Duke of Northumberland's gardener at Syon House at that time.

The plant seems to flower most prolifically if it's confined to pots that are not too large and is kept fairly dry in winter.

Bibliographic references: [1] Planta 174, 242-247 (1988); [2] Botanica Helvetica 116, 1-7 (2006)

Coral Drops, Bessera elegans, Asparagaceae

2011-09-16T20:13:00.000+01:00

Garden plants drift in and out of fashion and this vibrant, late summer-flowering species seems to have been well enough known in Edwardian times to feature in popular gardening dictionaries, but in half a century of gardening I'd never encountered it - until I found its bulbs on sale in a local garden centre earlier this year. In The Illustrated Dictionary of Gardening, edited by George Nicholson who was Curator at the Royal Botanic Gardens, Kew in the latter years of the 19th. century, it's described as "an elegant little half-hardy, squill-like bulbous plant from Mexico" and Nicholson's advice for growing it holds good today, even though the 'bulbs' he mentions are actually corms. "It requires good drainage [and] .... if cultivated in pots, a plentiful supply of water from commencement of growth until ripening off", he recommended. I've grown it in pots in my conservatory, followed his century-old instructions to the letter and been rewarded this month with a display of these scarlet flowers, with their blue stamens and style. They're held aloft on 30cm.tall stems, as shown in the illustration below that must have been produced at around the time that the plant was first grown in British gardens. It deserves to be more widely grown today, even though it's not hardy - so you need to dry off and store its corms after the foliage dies down in autumn.

There seems to be some controversy about the classificaton of the plant and the Pacific Bulb Society, which has some useful information on the species, mentions that recent opinion places it in the family Themidaceae, whch I've never encountered before. Their web site illustrates a strikingly coloured purple cultivar and also mentions that Bessera may be synonymous with the very similar genus Behria: all very confusing.

[Image from Edwards's Botanical Register; Consisting of Coloured Figures of Exotic Plants Cultivated in British Gardens; with their History and Mode of Treatment. London 25: t. 34 (1839). Source: http://en.wikipedia.org/wiki/File:34_Bessera_elegans.jpg ]

Dodder, Cuscuta sp., Convolvulaceae

2011-08-10T10:35:00.000+01:00

Mel, over at Sandy Wildlife has posted a fascinating piece about Dodder Cuscuta europaea, one of the most interesting British native flowering species, that has no root system of its own but parasitises other plants. Her post (highly recommended) is full of fascinating information about the plant and its history but I thought I would add a little about growing it. Some years ago I was given some dodder seed, which I germinated on wet paper towel (germination took about a week), then transferred the spindly seedlings to the soil surface around the base of a stinging nettle Urtica dioica plant in a flower pot. The seedlings elongate quickly and the yellow growing point rotates in a circular motion as it elongates (circumnutation) , until it touches the host plant stem. Once it makes contact there is a delay of a few days and them something remarkable happens...

........ the slender thread swells massively and then coils around the host stem. At this stage it looks more like a reptile than a plant. This transformation takes place because the dodder shoot tip has produced an invasive haustorium that has penetrated the host stem and linked up with its victim's vascular tissue, so now it can divert nutrients from its host to support the new aggressive phase of growth.

After that invasion is very rapid. The dodder branches and wherever it makes contact with the host it 'plugs-in' another haustorium - here you can see haustoria penerating the nettle stem, just a little way up from the bottom of the photo above. It often coils around itself but it seems that the haustoria can't penetrate the plant's own stems.

This is a thin transverse section, just one cell thick, cut through the point of contact between the dodder and nettle stems, seen under the microscope. The dodder stem is the darker tissue, top left, and you can see its haustorium puncturing the outer layers of nettle stem cells. If you look closely (click for a larger image) you can see the tip of the haustorium dividing into finger-like files of cells that are heading towards the host's vascular bundles (labelled V) that are conducting water, minerals and sugars within the nettle.

Once multiple haustoria have established the parasitic dodder grows very rapidly and then....

... flowers prolifically. The small white flowers are produced in clusters. A fascinating plant - a vampire of the vegetable kingdom.

Garden Nasturtium, Tropaeolum majus, Tropaeolaceae

2011-07-30T23:08:00.000+01:00

I think garden nasturtiums Tropaeolum majus were probably the first plants that I ever grew when I was a child. They are perfect for kids - large seeds for small fingers, reliably fast-growing, tolerant of almost any soil, colourful, long-flowering and harmless (edible, even).

Tropaeolum majus comes from South America, from the Andean foothills from Bolivia to Columbia, and has been grown in Britain since around 1686. It naturally has orange flowers, as in the top photo here, and grows in the wild as a climber, with prehensile leaf stalks (petioles). Successive cycles of selection and possibly hybridisation produced numerous varieties including dwarf, compact (Tom Thumb) forms and double cultivars that were popular in Victorian and Edwardian Britain. Today it's almost always raised from seed but in the 19th. century numerous named varieties were bred and propagated from cuttings that were overwintered in heated greenhouses, and were said by William Robinson, in his English Flower Garden, to produce more flowers and fewer leaves if grown in this way.

There are various accounts as to how the plant acquired its generic name. All say that Tropaeolum owes its name to the martial connotations of its shield-like leaves and helmet-like flower shape, but there are differing opinions on whether the name was derived from Greek or Latin. In Roman times a tropeum was a trophy pole used to display the armour and helmets of vanquished enemies, and some say Linnaeus consequently used the derived name Tropaeolum for the genus, recognising that the leaves resembled shields and the flower, when tilted downwards, looked like an elaborate helmet. Others say that Linnaeus derived the generic name from the Greek tropaion, meaning a trophy, for essentially the same reason

Nasturtium nectar is hidden deep inside the long spur (see top photo) formed from the sepals and long-tongued insects have to force their way into the mouth of the flower to reach it, although I have seen bumblebees that have learned to go around to the back of the flower and bit through the nectar spur to reach the nectar. John Gerard, in his General Historie of Plantes, mentions that these flowers were also known as lark's heel, on account of the spur that resembles the claw on a lark's foot.

There was, until recently, considerable debate about the evolutionary relationships of the garden nasturtium family, the Tropaeolaceae, with other plant families and for a long time it was belived to be related to geraniums (Geraniaceae), but modern molecular biological techniques, using DNA sequencing, shows that it is related to the cabbage family (Brassicaceae) and is one of 15 related families that all contain compounds called glucosinolates.

Interestingly, the large white butterfly Pieris brassicae that breeds on cabbage also took to breeding on this South American plant when it was introduced to Britain. I suspect that the butterfly's sensitive antennae, attuned to detecting the volatile chemical signals that identify suitable food plants for its caterpillars, must have detected the biochemical similarities between garden nasturtium and cabbage long before biochemists came to the same conclusion.

Plantago major rosularis, Plantaginaceae

2011-06-25T22:41:00.000+01:00

This strange mutant of the greater plantain Plantago major has been documented for over 400 years. It's commonly known as the rose plantain and at first sight the flower bears little relation to....

... the flower spike of the normal wild-type plant. Greater plantain could be described as one of the dullest flowering plants in the British flora, but the 'rose' mutant is really something rather extraordinary.

Mutants like this were described and depicted in John Gerard's Herball or General Historie of Plants, published in 1597, and have been grown as curiosities in gardens ever since.

Four hundred years after the woodcuts of mutant greater plantains appeared in Gerard's Herball you can still buy seeds of similar plants.

The normal inflorescence of greater plantain looks like a green rat's tail and to appreciate it's relationship with this green rose-like structure you first need to look at the mutant inflorescence in side view, when.....

... you can see that it's composed of a spiral whorl of spoon-shaped bracts. If you compare these with .....

... the individual flowers of a short section of the spike of the wild-type plant you'll see that the latter has a tiny green leafy bract under each individual flower. All that has happened in the mutant is that the tiny bract has just kept on growing, until it has produced a large green petal-like structure under each flower. The other effect of the mutant has been to stop the elongation of the inflorescence spike, so the longitudinal axis has been telescoped, producing a rose-like inflorecence.

If you look at the basal green 'petals' of the rose mutant you can see the other floral parts - the ovary (beginning to swell) and the withered stigma and stamens - sitting there at its base, just as they do in the wild-type.

Here I've cut the whole mutant inflorescence vertically in half so you can see the compressed longitudinal axis. If these green enlarged bracts were brightly coloured you'd be looking at a rather attractive inflorescence!

Looking a little closer still, here you can see an ovary (that will become the seed capsule) at the base of each leafy bract and brown, withered stamens. Normally greater plantain is wind pollinated but it's almost impossible for pollen to escape from between those large green bracts, so the individual flowers always self-pollinate - which is why this mutant, first mentioned in Gerard's Herball four centuries ago, has bred true every since, has survived unchanged as a garden cultivar and can be reliably raised from a packet of seeds. If this mutant had been able to cross pollinate with the wild type it would be a rare occurrence, turning up sporadically in large populations of the plant.

So, apart from being a botanical curiosity, what else can this mutant tell us about the formation of flowers? Well, it shows how a simple mutation, that allows the bract growth process to go on for longer than normal but turns off the inflorescence elongation process too soon, can have a spectacular effect on the final appearance of a flower and its structures. It demonstrates that a small shift in the timing of developmental events can have a dramatic final outcome, making simple structures more complex (or vice-versa, because it can operate in the reverse direction too). It illustrates how such changes in the development of various components of the flower could have led to the evolution of great variety of flower forms we see today. These days plant scientists studying the genes that produce a flower create artificial mutants of the experimental plant thale cress Arabidopsis thaliana to work out which genes affect the development of each component of the flower and how they interact with one another to produce its final structure. This 400 year-old mutant, known to John Gerard (who was a noted plagiarist and most probably copied the information from earlier herbalists), gives us another insight into that process.

Cocao,Theobroma cacao,Malvaceae

2011-06-03T21:03:00.002+01:00

I like a nice cup of cacoa - and this is where it comes from. This is the flower of cacao, Theobroma cacao, source of chocolate. These flowers - only about a centimetre across - are pollinated by small insects - notably midges - and then the cacao pod develops (see below).

The tiny cacao flowers are produced in large numbers and are unusual in that they sprout directly from the bark of the tree - a botanical trait known as cauliflory. The plant was formerly classified in the family in the family Sterculiaceae but more recent systematic research has reclassified it as a member of the mallow family. It originates from the foothills of the equatorial Andes and is thought to have been first domesticated 3000 years ago in Central America, where it became the sacred beverage plant of the Mayans, who believed it was a gift from the gods - a historical link commemorated in the Latin name that Linnaeus bestowed on the plant - Theobroma literally means 'food of the gods'. The Aztecs used cacao beans as a form of currency.

To produce chocolate the cacao pods are split open and the seeds are extracted from the pulp, then allowed to ferment for several days and then roasted (when the chocolate flavour develops), then ground into a powder. The highest-valued Criollo cacao has relatively low levels of bitter substances but cacoa powder is usually mixed with milk to offset the bitterness. About 3.7 million tons are produced annually to satisfy chocaholic cravings, much of it in West Africa, but about 30 per cent of the crop is lost to pests and diseases. It's hoped that the recent sequencing of the cacao genome will speed-up the selection of disease resistant varieties.

This gent - Sir Hans Sloane, 1660-1753, commemorated with this statue in Chelsea Physic Garden , of which he was patron - is credited with bringing cacao to Britain from Jamaica. Sloane was a physician and was interested in its medicinal properties but found that it was far more palatable if mixed with milk, inventing a patented recipe for milk chocolate that was eventually acquired by Cadbury. The original Cadbury's chocolate wrappers carried the inscription Sir Hans Sloane's Milk Chocolate prepared after the original recipe.

Sloane's belief in the medicinal properties of chocolate have been echoed for over a century in this illustration on the tin of Droste's cacao, a Dutch brand - where a nurse is shown delivering the drink to the patient. Notice how the image on the tin is repeated in the tin she is carrying on her tray - this cunning advertising image reinforcement, of an advert within an advert, has become known as the Droste Effect.

Adam's Laburnum, +Laburnocytisus adami, Fabaceae

2011-05-19T20:45:00.000+01:00

In 1825 a French nurseryman called Monsieur Adam grafted a purple-flowered specimen of broom Chamaecytisus purpureus onto a yellow laburnum Laburnum anagyroides stem, hoping to create the broom equivalent of a standard rose. Instead he created a strange graft chimaera - a tree with the tissues of both parents intermingled, that produces three different kinds of flowers. The core of the tree is laburnum, sheathed in layers of broom cells, and the whole arrangement is unstable. In the picture above you can see what appears to be a broom bush sprouting from the branch of the tree, looking like an unusually colourful mistletoe.

This picture, and the one below, show the profusion of purple broom flowers on slender, pliable stems......

... and is probably quite close to what Adam had in mind when he started his experiment, except that he would have hoped to produce this head of flowers on top of a single straight stem.

The whole tree, which looks like a rather lax, poorly growing laburnum in general shape, produces a second form of inflorescence .....

.... that looks like a dangling salmon-pink laburnum blossom - a blend of flower colours of both parents.

Look closely and you can see a hint of laburnum yellow towards the rear of these flowers ....

... but higher up on the tree, amongst the pink blooms, it also produces occasional pure yellow, typical laburnum flowers....

... which you can see here.

This example, of what is a rather rare tree, is currently flowering in Durham University Botanic Garden

In graft hybrids like this the cells of both parents coexist as separate genetic entities in a single organism. You could, at least theoretically, extract cells of each component, put them through sterile tissue culture and recover the two original parents. A similar graft hybrid between hawthorn and medlar, +Crataegomespilus, has also been produced but is rarely found in collections. The + before the Latin name indicates that the plant is a blend of cells from two parents that maintain their independent genetic identity, rather than being the result of sexual hybridisation.

Grafting, which has been most often used in viticulture, fruit tree and rose production was once viewed by many as being a very unnatural practice, comparable with the way many view genetic engineering today. In his poem The Mower, Against Gardens, Andrew Marvell (1621-1678) wrote:

Another world was searched through oceans new,

To find the marvel of Peru;
And yet these rarities might be allowed
To man, that sovereign thing and proud, Had he not dealt between the bark and tree,
Forbidden mixtures there to see.
No plant now knew the stock from which it came ;
He grafts upon the wild the tame,
That the uncertain and adulterate fruit
Might put the palate in dispute.

Genetic engineering has yet to produce anything in the horticultural world that's as extraordinary as Adam's Laburnum.

Aeonium arboreum,Crassulaceae

2011-05-16T22:32:00.000+01:00

I can't remember how long I've had this Aeonium - it must be a decade at least - and throughout that time it has produced nothing but these geometrically attractive spiral whorls of succulent leaves on a woody stem that.....

... bears a spiral pattern of leaf scars left by the old leaves that die and fall off.

This year it has finally switched into flowering mode and produced a spectacular inflorescence. The whole plant is about a metre tall.

This will be its final hurrah - like some bamboos and the century plant Agave americana, Aeonium arboreum is monocarpic , gradually accumulating the stored energy required to produce its flowers and seeds and then dying.

Botanical trivia: Aeonium is the only genus I can think of that contains all five vowels in a single name - useful to contemplate, maybe, if you are compiling quiz questions for your gardening club?

Sundew, Drosera binata, Droseraceae

2011-05-10T15:26:00.000+01:00

I've had this specimen of fork-leaved sundew Drosera binata for about a decade and it now fills a 10 inch pot and carries about 200 sticky-tentacled leaves. It's a death-trap for flies and would be quite capable of catching bumblebees if it had access to them.

Sundews face a dilemma - the need to capture and digest flies to supplement the meagre supplies of nitrogen in the soils in which they grow, while simultaneously using the services of insects to pollinate their flowers. The solution, as in many insectivorous plants, is to separate flowers and lethal leaves with a long flower stalk. It works pretty well in this case - the plant always sets plenty of dust-like seeds that germinate easily in surrounding flower pots in the conservatory, provided their soil surface is wet.

I particularly like the way the forked leaves unfurl - it's a bit like rolling out a deadly red carpet for passing insects ....

... and there is an air of menace about it in the final stages - like raised arms with clenched fists. The common name of the plant is especially apt - it looks stunning when it catches the first rays of sun in the morning, when all those drops of mucilage sparkle like dew-drops.

Sundews were amongst Charles Darwin's favourite plants and he experimented with them in great detail, demonstrating that they released digestive enzymes when presented with animal protein (egg albumen in his experiments).

He noted that when a few tentacles captured a fly the surrounding ones responded by curling towards and then over it, often followed by the whole leaf folding over the prey, creating what he referred to as a 'vegetable stomach'. You can see how some of the longer hairs are curling towards this fly within a couple of minutes of it becoming stuck.

Each sticky-tipped hair is a complex strucure, with a glandular head that secretes mucilage (which is remarkably resistant to being washed away) and then enzymes that digest the prey after it dies of exhaustion during its struggle to escape. The products of digestion are transported down the stalk to the leaf in a double layer of cells in the hair stalk that pass the digestion products from cell to cell.

Darwin's book Insectivorous Plants contains detailed accounts of his experiments with this plant and can be downloaded here.

Bird of Paradise flower, Strelitzia reginae,Strelitziaceae

2011-04-30T17:55:00.000+01:00

I've waited a long time for this. I bought this Strelitzia reginae as a small plant several years ago and made the fundamental mistake of planting it in a large pot, so it's been producing leaves rather than flowers until now. Back in November a flower bud appeared but its growth slowed right down in our unheated conservatory, but April's warmth has brought it into flower

There's no doubt that the Strelitzia bloom is very bird-like. It's also pollinated by birds - sunbirds - in its native South Africa

Hummingbirds in the New World hover in front of flowers and so burn up a lot of energy as they refuel with nectar, but sunbirds have a far more relaxed strategy, using the blue stamen of the flower as a perch

The stamen is a complex structure, formed by two elongated, fused blue petals and tipped with the white pointed stigma. The third blue petal that you can see here at its base is much smaller and conceals the nectar.

When the bird lands on the stamen its weight pushes it downwards, splitting the fused petals longitudinally and exposing the white pollen, which sticks to the bird's feet

When it visits another flower it lands on its stamen and while it's shuffling around probing for nectar it transfers pollen to the pointed white stigmatic surface that you can see above

A new flower rises from the inflorescence spathe every day. This is day two and I'm expecting three more

Image source: http://en.wikipedia.org/wiki/File:Charlotte1767Cotes.jpg

This is a flower deemed fit for a queen and was named by Sir Joseph Banks in honour of Charlotte of Mecklenburg-Strelitz (1744-1818), King George the Third's Queen-Consort, who was an avid botanist and great patron of Kew Gardens.

Puya chilensis, Bromeliaceae

2011-04-20T21:47:00.000+01:00

A few years ago I was given some seed of Puya chilensis that germinated quickly and produced attractive small pot plants that had one particularly annoying trait. The arching whorls of leaves were fringed with vicious little recurved spines that were forever catching in my clothes or lacerating my skin, so one by one I gave them away to friends who had more space to grow them. On Tuesday, when I visited the National Botanic Garden of Wales I rather regretted that I hadn't been more patient, because their Puya chilensis had a magnificent three metre-tall flower spike. If I'd hung onto my plants for another decade, maybe............

.... or maybe not. I'd probably be permanently scarred by the Puya leaves by now, and you really need a glasshouse like that at the NBGW to flower this magnificent plant reliably. In the wild those recurved spines in the leaves have been known to impale birds and small mammals.

Puya chilensis comes from the coastal mountains of Chile and can be grown outside here in the mildest frost-free areas of Britain, such as the Tresco on the Scilly Isles. But what you really need is ......

........ a glasshouse like this - the magnificent structure designed by Sir Norman Foster for the NBGW.

This is the largest single-span glasshouse in the world, dedicated to displaying the flora of our planet's hotter, drier regions.

The stunning architecture of the building complements the natural architecture of the plants that it houses..........

........ while at the same time blending with its natural surroundings.

The glasshouse follows the contours of the land and reminds me of the carapace of a tortoise. A truely inspirational structure in an inspirational new botanic garden run by passionately committed, enthusiastic people.

Walnut, Juglans regia, Juglandaceae

2011-04-06T21:16:00.000+01:00

When I was a kid my grandfather used to make little boats with half-walnut shells, fitting them with a matchstick mast and paper sail. Their association with childhood pleasures goes back a long way - apparently the Romans had a ritual at weddings whereby the bridegroom threw walnuts to children, symbolising the casting off of childhood preoccupations and the beginning of adult life.

One of the many botanically interesting aspects of walnuts is that they are not - botanically speaking - nuts. They are classified as drupes - fruits with a fleshy outer coating and a single hard seed inside, which groups them with peaches and plums whose outer coat is succulent. The tough outer coat of walnuts eventually splits to release the hard seed inside but it has its own special properties - it produces a deep brown dye. I discovered this for myself by accident when I was showing some visitors around Durham University Botanic Garden and picked up a fallen fruit and idly pulled it apart to show them the walnut seed inside - and it took three days for the brown stains to disappear from my fingers.

For about twenty years I had a walnut tree in my own small garden but it was foolish to plant such a fast-growing forest tree in such a small plot. It quickly outgrew the garden and I had to cut it down - and that revealed another interesting sensory aspect of the tree - its foliage and wood have a distinctive fragrance, that to me smells of apricots.

Walnut produces male and female reproductive structures separately on the same tree (monoecy) - the male flower being these fat catkins....

........... and the female being the ovary with a short style and twin stigmas that you can see between the leaf stalks at the top of the picture above. Solitary trees sometimes fail to produce nuts because there is a time differential between stigmas becoming receptive and the catkins shedding pollen (dichogamy).

Aside from its edible 'nuts', which were always an enduring feature of Christmas in our house when I was a child (no one could ever find the nut-crackers, which were not as elegant as the pair you can see here), walnut is famous for the beauty of its timber which is widely used for cabinet-making and for gun stocks. The tree originates from extreme south-east Europe and the Near-East (hence the alternative name Persian walnut) and can be killed in extreme winters. In 1709 there was a winter in Europe that killed thousands of walnut trees, which were felled and bought by Dutch merchants who foresaw an impending shortage and made a handsome profit by cornering the market for walnut timber in the years before new trees could be established.

There is an old saying that walnut trees are more fruitful if their branches are beaten. The likely origin of this is that walnuts used to be harvested as soon as they began to ripen, while still attached to the tree, by knocking them down with long poles - otherwise birds and squirrels would get them first. This assault on the tree broke the tips of twigs and promoted the growth of fruiting spurs, producing a better crop of fruits in the following year.

Forsythia x intermedia, Oleaceae

2011-03-31T11:27:00.000+01:00

Few shrubs are as easy to cultivate ("in almost any soil short of a bog": Graham Stuart Thomas) or provide such a reliable display of spring flowers as Forsythia, so it's hardly surprising that its blooms light up suburban gardens everywhere at this time of year. This fine specimen was flowering on the banks of the River Tyne at Wylam yesterday, with its mass of blooms contrasting with the still-leafless branches of the trees on the riverbank.

The modern Forsythia Forsythia x intermedia is a hybrid between F. suspensa and F. viridissima, first produced in the 1880s and since reproduced with various improvements on numerous occasions by intercrossing these two species, both originating from China. The parental species are not seen very often in cultivation these days. F. suspensa has long, trailing shoots that William Robinson, in his English Flower Garden (1883), suggested looked best when they were either trailed over a sunny wall or secured to it (when "the long, slender branchlets dispose themselves in a very graceful manner"). It flowers all along its shoots, so to achieve the best display of blooms at least some of the long shoots should not be pruned. In contrast the hybrid, which inherits its shrubby stature from F. viridissima, flowers on side shoots, so some shortening of long shoots immediately after flowering keeps the plant reasonably compact and still guarantees a mass of golden blooms in the following spring; I've seen some very striking, quite formal flowering hedges created with this species.

An important factor in the popularity of Forsythia is that its flower buds are not damaged by hard frosts in March. Some research at Purdue University back in 1995 indicated that this was at least partly due to the fact that the flower tissues accumulate soluble sugars, that protect the cells from catastrophic effects of freezing.
It's quite often stated that Forsythia flowers contain the carbohydrate lactose, which is otherwise only found in milk secreted by the mammary glands of mammals. I'm not sure how this claim originated, but a study by biochemists at Tohoku University in Japan in 1991 failed to find any trace of lactose in the flowers.
Interestingly, in 1998 genetic engineers at the National Institute for Agrobiological Resources at Ibaraki in Japan managed to express mammalian milk proteins in tobacco plants, for potential pharmaceutical applications - a biochemical feat that half a billion years of plant evolution failed to achieve.

Buds

2011-03-28T08:52:00.000+01:00

So here we are again, on the threshold of another gardening year - and surely there is nothing that epitomises the gardener's feelings of hope and expectation more than a flower bud at the point of opening.

It's worth leaning on your garden spade, taking a breather from digging and contemplating the mind-boggling processes that have taken place inside a flower bud in the months, days and weeks that have led up to this moment. Somewhere in the apex of the plant tissues a group of cells has become committed to becoming a flower rather than developing into leaves. They've undergone a precise series of divisions and choreographed cell expansions that has produced an embryonic flower, tightly packaged in a bud that only requires a little warmth and a surge of water coursing through its tissues to expand into its full glory.

It's been weeks in the making - months in the case of bulbous species like bluebell whose flower initials were formed in the bulb last year - and as soon as the flower has done its job and attracted a pollinator it will collapse and die. I can think of nothing in nature where the combination of structure and function have evolved to an extent that is so aesthetically satisfying - or so fleeting; the product of hundreds of millions of years of evolution, the individual life of flower is measured in days.

Say It With Flowers

2011-03-14T21:01:00.000Z

When did you last receive of bouquet of flowers from an admirer? Recently, I hope. But did you take a really close look at the kinds of flowers that came? Perhaps not. A century ago - back in Victorian and Edwardian times - the gift of flowers was loaded with hidden meaning. They had a language all of their own. At the tail end of the nineteen century and into the early twentieth century people really did ‘say it with flowers’, and the wrong choice of species could land you in serious trouble. No refined lady could afford to be without the latest edition of that indispensable manual of floral etiquette in polite society, The Language of Flowers. This copy belonged to my grandmother.

Each different species of flower conveyed a powerful message and arrival of the florist at the door would see the lady of the house flicking through the pages of the manual, decoding the bouquet. A camellia sent as a compliment symbolised 'perfect loveliness', while a pot of basil was a declaration of 'hatred'.

The layout of the book was simple and convenient. The first half contained a list of flowers with their meaning, the second half a list of sentiments and the flowers that expressed them. With successive editions the meanings were sometimes changed a little, which might have made these floral conversations a little tricky if you didn't remain au fait with the latest flowery language.

Botanically speaking, a burgeoning relationship might go something like this. Smitten by desire, a young suitor might send the girl of his dreams a single Coreopsis bloom, a declaration of 'love at first sight'. He’d be hoping for the return of a daisy, meaning ‘I share your sentiments’. Most often, I suspect, the lady would have been more circumspect. She might want to reassure herself first that her suitor was well-healed, and despatch a kingcup (‘desire of riches’). Recognising he’d hooked a gold-digger, he might respond with a scarlet poppy ( promising ‘fantastic extravagance’), unless he was hard up, in which case vernal grass (‘poor but happy’) would be the reply. If that was the case then a mesembryanthemum (‘your looks freeze me’) would leave him in no doubt that further advances would be to no avail until he'd made his fortune.

It might all end there, but perhaps pride and outrage would trigger one final exchange of floral abuse. The swift despatch of pasque flowers (‘you have no charms’) from him, followed by Scotch thistle (‘retaliation’) and tansy (‘I declare war against you’) from her might open hostilities. If they really wanted to be abusive the spurned suitor might send the florist staggering up the garden path under the weight of a water melon (hinting at a tendency towards ‘bulkiness’ in the addressee).

Or perhaps his initial advances might be more successful. The opening exchange of coreopsis and daisies might escalate into something decidedly steamier. Pressing home his early success with orange blossom (‘your purity equals your loveliness’) might trigger a reply of a peony (‘bashfulness’) and marjoram (‘blushes’). Time for a bit more flattery with a damask rose (alluding to her ‘brilliant complexion’), in the hope that peach blossom (‘I am your captive’) might coming winging back through the post. If it did, he might risk despatching tuberose (hinting at ‘dangerous pleasures’), keeping his fingers crossed that the reply would be an African marigold (admonishing him for his ‘vulgar mind’) – a sort of Victorian “Ooooo! You are awful” – and not a dried white rose (indicating that ‘death is preferable to loss of innocence’).

If the African marigold arrived the swift despatch of a cuckoo pint (an unequivocal symbol of ‘ardour’) would leave her in no doubt as to what he had in mind, so she could safely despatch a white ditanny flower (hinting at ‘passion’), confirming her willingness to live dangerously .

But by then all those visits to the florist would have set the servants’ tongues wagging. A Cobaea bloom (warning of ‘gossip’) would set alarm bells clanging and would call for the despatch of mandrake (as an expression of ‘horror’) in return. A hellebore bloom (symbolising a whiff of ‘scandal’) would break the bad news that this wild botanical courtship had become talk of the town, so finally the suitor must be forced to do the decent thing and - pausing briefly to contemplate the folly of loose floral talk and the effect on his bank balance before he let his letter slide into the postbox – despatch a lime leaf ('marriage').

No wonder Victorian courtships were such drawn out affairs, if lovers had to scour gardens, florists and the countryside to find just the right flowers to convey their feelings. Where could you get a red columbine in January, if you wanted to tell your betrothed that you were ‘trembling with anxiety’? How inconvenient (and ecologically irresponsible) to have to scour the countryside for a frog orchid to convey your ‘disgust’ at their conduct. The Language of Flowers must surely be the most impractical form of communication ever devised...... but this genteel form of dialogue was infinitely more romantic than the modern text message - and often fragrant too.

Maybe there is still someone out there who respects the old niceties of polite society. So keep a daisy to hand, just in case you receive an unexpected twig of spindle tree (‘your charms are engraved on my heart’) or a pineapple (‘you are perfect’). But if you do decide to respond, better get hold of a copy of The Language of Flowers first. There’s no telling where this botanical banter might lead.

The fly-leaf of my grandmother's copy bears this inscription: To Miss Nancy Fox, with every good wish from Mr. John Smith, 21st.August 1920 and it bears a cut-out picture of a pansy, which conveyed the message 'You Occupy my Thoughts'. At first sight that's a little odd, because she didn't marry a John Smith. So was this a rejected suitor? I suspect not. John Smith is not a very convincing name, is it? I suspect it was my grandad, Harry. At that time he had recently returned as a wounded soldier from the Great War. She was a young teenager, employed by a local nursery to hand-write invoices, on account of her love of flowers and beautiful script handwriting - the only school qualification she had. This might have been his first advance, in which he thought it proper to conceal his real identify, hoping that his gift would be the start of a floral courtship. We'll never know for sure, but she kept this little book until the day she died.

Honeysuckle or Woodbine, Lonicera periclymenum, Caprifoliaceae

2011-03-08T21:43:00.001Z

“The beauty and fragrance of its flowers make it a welcome guest in our gardens, hedges and arbours”, wrote William Withering in 1776, in his Botanical arrangement of all the Vegetables Naturally growing in Great Britain. For my money none of the cultivated varieties quite match the scent of the wild species, emitting its scent on a warm, still summer night in a country lane. The wild plants seem to have paler, yellower flowers without so much of the purple pigment. Honeysuckle only flowers well if it's in a sunny position and to achieve that it climbs, sometimes to the top of trees, but it's at its best when it climbs through a hedge.

The scent is emitted just as disk falls, attracting moth pollinators, notably hawk-moths that hover with long probosces extended just in front of the flowers, which is why ...

... the stamens and stigma are so long - to make contact with the hovering pollinator.

After pollination the berries that form are a great attraction for blackbirds. By one of those happy accidents in gardening, they've perched on our otherwise dull leylandii hedge and voided the seeds in their droppings, so honeysuckle has clambered up through the conifers, which have become a wall of scent on summer evenings.

That in turn has brought this delightful little moth into the garden - the twenty plume moth Alucita hexadactyla, which breeds on the honeysuckle and is strongly attracted to light, setting on the lit wndows of the house after dark. Back in 1776 William Withering noted that several moths visited honeysuckle: “The insects that have been observed to feed on the honeysuckle include the Priver Hawk Moth Sphinx ligustri, the brown feathered moth, Phalaena didactyla, the small bee moth, Sphinx tipuliformis, and the many feathered moth Phalaena hexadactyla”. I think this is the latter, after a change of Latin name.

Some cultivars continue to produce flowers right through until the first frosts - as this one did - but there are also winter-flowering species that bring fragrance to the dullest months of the year.

This is Lonicera x purpusii that begins flowering outside our conservatory door in January. A few sprigs in a vase will scent a whole room.

Given the opportunity, honeysuckle will climb to the tops of small trees, curling around the trunk for support, which is why it acquired the alternative name of woodbine. John Gerard , writing in his Great herball or Generall Historie of Plantes in 1597, described how “Wood-binde or Hony-suckle climeth up aloft, having long slender woody branches........oftentimes winding it selfe so straight and hard about, that it leaveth its print upon those things so wrapped”.

This is what he meant. It puts me in mind of this statue.

For a closer look at the strangling tendencies of honeysuckle, take a look at this.

Primrose, Primula vulgaris, Primulaceae

2011-02-19T17:12:00.000Z

With the possible exception of the bluebell, the primrose Primula vulgaris is probably Britain's most popular spring flower. Even now, on a freezing mid-February day, new leaves and flower buds are beginning to form in primroses in woodlands here in north-east England. Primroses have been grown in gardens for centuries - probably since people first cultivated gardens - giving rise to numerous varieties and, through hybridisation with cowslips, the garden polyanthus. The primrose also excited Charles Darwin's curiosity, in his struggle to understand and define the nature of species. Like many before him, he was aware that ...

........ primroses, with their large single flowers, grew along woodland edges and hedgebanks....

... while cowslips, with their numerous small flowers on a common stalk, grew in pastures, but...

... wherever the two coincided they hybridised to produce false oxlips, with large flowers on a common stalk. Although every field guide to wild flowers describes primroses and cowslips as distinct species, in evolutionary terms they are really one - a genetically diverse species with a wide range of variation which, at its extremes, produces distinctive plants that are adapted to life in woodlands or grasslands. Primroses and cowslips are on the way to becoming two separate species, where they would satisfy the modern evolutionary biologist's absolute definition of a species, based on an inability to interbreed with other related species, but they haven't reached that point yet. No wonder this example of evolution-in-progress attracted Darwin's inquiring eye.

Ever since primroses and the primrose-cowslip false oxlips hybrids were introduced into gardens they have been exchanging their genes with other cultivated Primula species from the European mainland, introducing new flower colour genes that give us the range of brilliant hues that are available in garden centres today. Sometimes the gene exchange extends beyond the garden and back into the wild - as, for example, in the primrose you can see here.

Darwin was fascinated by primroses for another reason. His Cambridge University botany teacher and mentor, John Stevens Henslow, drew his attention to the fact that there are two kinds of flowers in any wild population of primroses...

....so-called pin-eyed flowers, with the stigma at the end of a long style, level with the top of the corolla tube...

... and with the stamens located way down in the corolla tube, as you can see in this sectioned flower...

... and thrum-eyed flowers, like this, where the stamens are at the top of the corolla tube...

... and where the stigma, at the end of a much shorter style, is located way down in the corolla tube.

The presence of two forms of flowers in the population is known as heterostyly and Darwin made numerous self- and cross-pollinations between the two forms, demonstrating that self-pollination failed and that crossing beween the two forms was necessary for seed set, and also that the differential placement of the stigma and stamens in the two forms aided cross pollination between them by insects. In his autobiography he remarked "No little discovery of mine ever gave me so much pleasure as the making out of the meaning of heterostyled flowers"

The two forms were illustrated in diagrammatic form in this publication: Darwin, C. R. 1862. On the two forms, or dimorphic condition, in the species of Primula, and on their remarkable sexual relations. [Read 21 November 1861] Journal of the Proceedings of the Linnean Society of London (Botany) 6: 77-96.

The scientific study of this floral arrangement has yet to run its course and, 150 years after Darwin first described the mechanism, the genes that control the development of the two primrose flower types are currently under investigation by Professor Phil Gilmartin at Durham University.

Darwin wasn't the only eminent Victorian to be beguiled by this flower. Primroses were the favourite flower of Benjamin Disraeli, Prime Minister in two Conservative governments during Queen Victoria's reign. Such was her affection for him that she sent a wreath of primroses to his funeral on 19th. April 1881. Thereafter that date was celebrated annually as Primrose Day.

Disraeli image source: http://upload.wikimedia.org/wikipedia/commons/0/0c/Benjamin_Disraeli_by_Cornelius_Jabez_Hughes%2C_1878.jpg

Passion Flower, Passiflora citrina, Passifloraceae

2011-02-02T20:16:00.000Z

Passion flowers Passiflora spp. are amongst the most elaborate of all flowers but I particularly like the relative simplicity of this diminutive species, Passiflora citrina which hails from the hills of western Honduras and eastern Guatemala. Its mountain origins mean that it does well in a cool conservatory. The flowers are only a few centimetres long and the whole plant will happily grow in a large pot on a windowsill, trained up slender canes, where it will flower for months on end.

The structure of Passiflora blooms is unusual, with the ovary and stamens held aloft from the centre of the flower on a long column. It has been suggested that this arrangement evolved to avoid damage from visiting pollinators (usually bees, although large red-flowered species are visited by hummingbirds) that probe for nectar at the base of the petals. Keeping the ovary - all important for seed production - out of harm's way will making sure that the visiting pollinator contacts those stamens and stigmas on the way in and out is a win-win strategy from the plant's perspective. The flowers are protandrous, meaning that the anthers shed their pollen first and then, once it has all been removed by pollinators, those three nail-shaped stigmas on top of the ovary move outwards and become receptive, so promoting cross pollination.

Passion flowers are loaded with religious symbolism, with the number of floral parts being taken by the faithful to symbolised various episodes in the life of Christ. For example, the ring of floral filaments is considered to represent the crown of thorns, the three stamens represent the nails used in the crucifixion and the five stamens represent the five wounds - usually with this species Passiflora caerulea being the 'typical' symbolic passion flower.

The edible passion flower P.edulis, like the one above, is easy to grow from the dimpled seeds in commercial passion fruits, although the flowers are quite small and lack the boldness and symmetry of P.caerulea. I've found that the best way to germinate these seeds, and those of many other tropical and subtropical plants like lychees, is to clean the seeds then put them in a polythene bag of moist peat (or a substitute like coir) and keep them in the airing cupboard near the hot water tank - remembering to check regularly for germination.

Butterwort, Pinguicula moranensis, Lentibulariaceae

2011-01-13T20:12:00.000Z

Carnivorous plants have a problem. On the one hand, they must catch and digest insects to supplement the meagre soil nitrogen supplies in the boggy habitats that they inhabit. On the other hand, they depend on insects to pollinate their flowers, so there is no future in 'biting the hands that feed them' to the extend that they produce no seed. So most tend to have flowers that are well separated from their lethal, carnivorous leaves by a long flower stem - and this attractive butterwort from Mexico, Pinguicula moranensis, is no exception.

This species makes an excellent plant for the cool conservatory, for two reasons. One is that it produces these attractive magenta blooms from late autumn right through until early summer.

The second reason is that it's a formidable consumer of several annoying greenhouse pests, including whitefly, greenfly and those annoying little mushroom gnats that tend to come with many brands of today's potting composts. The way in which small insects are attracted to the glutinous glands on the leaves and are then trapped and digested is very satisying - and you can see some examples of butterwort's insect catching prowess here. This plant is flowering flypaper.

This species is very easy plant to propagate - just pull the leaves away from the leaf rosette and insert each to a depth of about 5mm. in a moist compost. Buds will develop at each leaf base, to produce a new rosette, much as they do when you propagate an African violet or Streptocarpus species.

Place butterworts amongst your conservatory plants and they will act as a form of botanical biological insect control; they won't eliminate your pest problems but they will produce tangible evidence that they are making inroads into the insect pest population. This plant comes with a feelgood factor if you are troubled by tiny winged insect pests.

Seen from the side, it's clear that this butterwort's flowers must be pollinated by long-tongued butterflies, landing in the flat-faced flower and probing with a long proboscis to the bottom of that long nectar spur behind the flower. The flower is the only part of the plant without adhsive and digestive glands - look closely at the flower stalk (double-click) and you can see here that it's coated with adhesive glands that have caught a few tiny greenfly.