Fairchild's Mule...... almost

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

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

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

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

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

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

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)