A Digital Botanic Garden

Beautiful buds

2013-04-27T19:39:00.000+01:00

One of the joys of spring is to watch buds develop and then burst - exquisite shapes with all the beauty of the flowers packaged within.

Daffodil

Aloe variegata

Sambucus racemosa

Blackcurrant

Horse chestnut

Hyacinth

Rhododendron dauricum

Erythronium 'Pagoda'

Marsh marigold Caltha palustris

Ash Fraxinus excelsior flower buds

Sycamore Acer pseudoplatanus

Pasque flower, Pulsatilla vulgaris, Ranunculaceae

2013-04-18T17:04:00.000+01:00

Pasque flower usually flowers in our garden around Eastertide, but this year an early Easter and an exceptionally late spring means that the flowers are only just opening. I particularly like the covering of fine silky hairs that trap water droplets on misty mornings.

Pulsatilla vulgaris is a rare and endangered species of calcareous grassland in England, now confined to just a few locations. Many of its old sites have been ploughed up. In the wild the plant often grows in nutrient-poor soils and is usually quite small, with only a couple of flowers, but cultivated varieties grown in better soil conditions are far more floriferous. The secret of long term cultivation seems to be to grow it in very well-drained soils in a sunny spot.

After the flowers have finished the feathery seed heads stay attached to the plant for several weeks. I've found that the best way to grow the plants from seed is to sow them soon after they're ripe - stored seed has much poorer germination.

It think it's a charming plant, nicely summed up by William Robinson in The English Flower Garden: "There are few sights more pleasant to the lover of spring flowers", he wrote, "than to see its purple blooms just showing through the hard grass on a bleak down on an early spring day".

Cyclamen hederifolium, Primulaceae

2013-03-12T10:24:00.000Z

I was never a great fan of Cyclamen until I started buying this little beauty, C.hederifolium, as a winter house plant. It ticks all the boxes: attractive foliage; compact and very floriferous form; long-lasting (some that I bought back in December are still in bloom); sweetly scented (at least the white-flowered varieties are - I can't detect much scent in the darker pink and red varieties); and it's cheap - the nursery where I buy them sells them for £1 each.

One particularly attractive feature of Cyclamen is the shape of the flower buds, that are twisted like the swirl of a dancer's skirt.

The only tricky thing about growing this little beauty is remembering not to over-water it. The densely packed leaves and flowers succumb to Botrytis at the stem bases if you do.

Viburnum x bodnantense 'Dawn', Adoxaceae

2013-02-05T17:54:00.000Z

The darkest days of winter in our garden have been brightened by the scented flowers of Viburnum bodnantense 'Dawn', which has been in bloom continuously since late November. The first flowers tend to be damaged by the worst of the winter weather but the recent ones, now it's a little milder, have a more intense colour. The twigs make good cut flowers for a small vase because the flowers are borne on their tips and open to perfection indoors.

V. x bodnantense is a hybrid between V. farreri and V. grandiflorum, raised at Bodnant in North Wales in 1935.

It used to be thought that Viburnum belonged to the honeysuckle family, Caprifoliaceae, but recent molecular studies using DNA sequencing have shown it to be a member of the family Adoxaceae. Forty years ago, when I was a trainee botanist, the Adoxaceae was believed to contain just a single species, town-hall clock Adoxa moschatellina but, as is so often the case, molecular biology has revealed unsuspected phylogenetic relationships.

White Magic

2013-01-14T21:43:00.000Z

Some snow adds a touch of magic to a botanic garden in winter. These pictures were taken today in Durham University Botanic Garden

Rhododendron dauricum and ..................

....Mahonia x media 'Charity'

Kniphofia spp., Red-hot Poker, Xanthorrhoeaceae, sub-family Asphodeloidea

2012-11-09T10:44:00.003Z

It came as a surprise to me that red-hot pokers thrive in my garden here in North East England. If you look at the distribution map of the species, through Africa and Madagascar, with an outlier in Yemen, you'd imagine that heat and dry conditions are a requirement but when you look at the habitats occupied by many of the species - cooler, higher altitude sites - maybe it's not so surprising that they do well in my flower borders. This summer, which was cool and wet, seems to have suited them pretty well......

.... especially this yellow-green flowered variety. I've lost its label but I think it might be 'Percy's Pride'. This plant produced 15 flower spikes and was in bloom for six weeks.

The best display of Kniphofia uvaria that I've ever see in Britain is this one, in the sand dunes on the Northumberland coast at Low Newton-by-the-sea where it is verging on becoming invasive They're not the conditions that would be easy to replicate in most gardens though.

I'm always interested in the native insects that visit exotic flowers in British gardens. In its native habitats Kniphofia is pollinated by sunbirds and each individual flower produces a large volume of nectar to attract these energetic pollinators. The nectar must trickle down those long, downward-pointing tubular flowers, because peacock butterflies seem to have no trouble in reaching it.

Access is more of a struggle for wasps, which will do almost anything to reach sweet nectar in autumn when they are no longer feeding their brood. This enterprising individual discovered that the easiest way to reach a reward was to chew a hole through the corolla ......

...... while this one chose to do it the hard way, forcing its way into a flower that really evolved to accommodate a sunbird's long, slender, curved beak.

Masterwort, Astrantia maxima and A. major., Umbelliferae

2012-08-10T20:55:00.001+01:00

Ever since masterwort Astrantia major was introduced into British gardens in 1597, from its native central and eastern Europe, garden writers have been somewhat dismissive of the plant. William Robinson, in The English Flower Garden in 1883 was wary of its invasive tendencies (".... apt to over-run and exhaust the soil") and suggested that "if grown at all it should be in rough or wild places, or in the back part of the shrubbery".

However, the species in the picture above, Astrantia maxima, is rather more delicate and trickier to cultivate, so is unlikely to be invasive. It needs better, more moisture-retentive soil than A. major.

It's easy to see why the more commonly cultivated A. major was sometimes known as 'hattie's pincushion" and why Graham Stuart Thomas, in his Perennial Garden Plants (1976) described the flowers as having "...an interesting and beautiful shape". .

It isn't obvious that this is a member of the Umbelliferae but if you shrink that ring of papery bracts and elongate the pedicels that support the individual florets the result is a more obvious umbel.

The plant has a long flowering period, seems to do well in sun, shade and dry soil in my garden, makes an attractive long-stemmed addition to a bunch of cut flowers and, best of all, is an excellent source of pollen and nectar for .....

... hoverflies ....

..... and bees, that merely need to walk over the inflorescence to collect their reward with minimum effort.

Monk'shood, Aconitum napellus, Ranunculaceae

2012-07-16T23:11:00.001+01:00

"Helmet-fluore, or the great Monkes-hood, beareth very faire and goodly blew floures in a shape like a helmet; which are so beautifull, that a man would think they were of some excellent vertue, but non est semper fides habenda fronti " wrote John Gerard in his herbal of 1597. And, indeed, appearances are not always to be trusted, because Gerard then went on to describe the dire consequences of eating this poisonous member of the buttercup family. "The force and facultie of Wolfs-bane [another common name for members of the monk'shood genus] is deadly to man and all kindes of beasts .......The symptoms that do follow those that doe eat of these deadly herbs are these; their lips and tongue swell forthwith, their eyes hang out, their thighes are stiffe, and their wits are taken from them."

But as long as you don't eat it, this is a fine plant for the herbaceous border, with the flowers of a violet-blue hue that's shared by wild columbine, another member of the same plant family.

Gerard noted that the plant was also found in alpine meadows "where you shall find the grasse that growth round it eaten by cattell, but no part of the herb it selfe touched, except by certain flies, who in such abundant measure swarme about the same that they cover the whole plant". He then describes how a confection made from twenty of these flies that are immune to monk'shood's poison was an "excellent remedy not only against the Aconites, but all other poisons whatsoever".

Looking at the rather sinister flowers from the side, it's easy to see where the names helmet-flower and monk'shood came from.

The nectaries of the flower are located way up inside the upper petal that forms the hood, where only long-tongued bees can reach it.

The flower is dependent on bumblebees for pollination and the strong bilateral symmetry of the flower means that they have to force their way in through this narrow opening, where they brush against the stamens and stigma as they struggle to reach the nectaries in the hood. The stamens ripen before the stigmas (protandry) and in this picture you can see a couple whose anthers have burst, shed their pollen and whose stamen filaments have elongated. There are six more whose anthers have burst to release white pollen but whose stamen filaments haven't elongated, but the majority of the numerous anthers present have yet to release their pollen.

I've posted some photos of bumblebees visiting the flowers here.

Giant Fennel, Ferula communis, Umbelliferae

2012-07-06T21:17:00.000+01:00

I've waited seven years for this.

Back in 2007 I bought a small plant of giant fennel Ferula communis, when I was mainly attracted by its delightful, ferny, four-pinnate foliage but also tempted by the promise of a giant inflorescence.

Every year since then it has produced a few magnificent leaves, almost a metre across, but has never showed any sign of flowering. Finally it has summoned up the energy to perform, which is remarkable on two counts.

Firstly, this is a plant from dry, rocky places in the Mediterranean - in countries like Greece - and this is cold, rainy Durham in northern England, in the grip of the wettest summer on record.

This is its natural habitat (image source)

Secondly, according to Marjorie Blamey and Christopher Grey-Wilson's Mediterranean Wild Flowers:

'The stems becomes hard and woody on drying ..... the pith, when dry, burns slowly inside the stem and can be carried alight - it may well have been the original Olympic torch'.

And, of course, this is the year when the Olympics come to Britain. Nice timing!

Other sources claim that the stems were used by Prometheus when he stole fire from the gods on Mount Olympus and gave it to humans.

The stem is robust - and has been used for making furniture, apparently - and the leaf bases sheath the stem in this very distinctive manner.

The inflorescence finally finished elongating when it was close to three metres tall ....

...... then its yellow umbels bloomed. The only way to photograph these is from the upstairs bedroom window......

........... although they do look attractive from below, against the sky.

It's also a very good 'bee-plant' attracting a constant procession of bumblebee visitors to these umbels, each of which is as big as my fist.

Worth waiting for!

Giant fennel is monocarpic and the plant will die after flowering, but I'm tempted to try that stem as a home-made Olympic torch....

Lupin, Lupinus spp., Fabaceae

2012-06-10T20:40:00.000+01:00

June is the peak month for lupin flowers, although they don't seem to be such popular border plants as they once were.

We have a family connection with lupin growing because in the 1920s my grandmother worked in Drayton Manor nursery, near Chichester in West Sussex, that specialised in growing Lupinus polyphyllus as a cut flower. This is a photo from the nursery catalogue, although the lady isn't my grandmother. The fields of flowers must have looked spectacular and I can remember as a child seeing feral descendants of these plants growing on the edge of gravel pits where the nursery once stood, and seeing them in Gran's garden. The sweet peppery scent of their flowers always triggers recollections of these stately blooms, with bees working their way methodically around and up each flower spike before moving on to the next.

Lupinus polyphyllus, which is naturally blue-flowered, was introduced from North America by the plant collector David Douglas in the 1820s and soon became a popular subject for the herbaceous border, which it graced until the Yorkshire gardener George Russell decided to try to produce plants with denser flower spikes in a wider range of colours.

Beginning just before the First World War, Russell grew thousands of lupins on his allotment and ruthlessly eliminated any that he thought sub-standard, favouring bi-coloured forms with closely spaced whorls of flowers on the flower spike. By the late 1930s he'd produced his famous Russell lupin strain and with the help of nurseryman James Baker propagated the best forms commercially from cuttings. The plants were a sensation at the 1937 Royal Horticuultural Society Chelsea Flower Show and Russell, at the age of 79, became famous, receiving an MBE and the RHS Veitch Memorial Medal for his efforts. He lived on until 1951, dying at the age of 94. Plant breeders do seem to live to a grand old age; perhaps it's the determination to see how seedlings from last year's cross pollinations will perform.

Russell probably intercrossed L. polyphyllus with other species (possibly with tree lupin and the annual L. nootkatensis) although we can't be sure because no pedigrees of cross pollinations were kept. It seems likely that he probably let bees do the intercrossing for him.

For anyone with space enough to grow the plants, breeding lupins can be rewarding , as the seedlings flower in the year after sowing. Crossing involves carefully emasculating the flowers while they were still in bud, by carefully opening the buds and removing the stamens before they can shed pollen and then, after a delay while the flower develops and the stigma matures, cross pollinating the stigma with pollen from another individual, or even another species which may or may not produce a viable hybrid seed.

Lupin flowers, like most legumes, have a distinctive and instantly recognisable flower morphology, with a prominent standard petal at the top and a folded keel petal, enveloping the stamens and the stigma, that's flanked by a wing petal on either side.

You can always spot a lupin flower that has been 'tripped' by visiting bees because their weight forces down the wing petals so the pointed tip of the keel petal protrudes.

During the bee's visit the keel petal is pushed downwards so the stigma at the tip of its long style is forced up through the end of the keel, sweeping a plug of pollen from the anthers before it and onto the underside of the bee. You can see the pollen as the yellow deposit on the tip of the keel petal and on the stigma in this photograph.

Plentiful pollen makes lupin flowers very attractive to bumblebees, so emasculated, cross pollinated flowers need to be covered to keep bees away until seed has set.

The most interesting lupin species that I've grown is this one - Lupinus mutabilis. It's an annual that comes from South America, where it's known as tarwi and is said to have been cultivated as a food crop by the Incas. It's seeds have very high levels of protein (40%+) and lipid (20%+) but from the horticultural point of view it's the colour and fragrance of the flowers that appeal. It's easy enough to grow provided you don't attempt to transplant it. It never recovers from the slightest root disturbance, so you either need to raise it in pots as a conservatory plant or sow it in the garden where you want it to flower.

Prickly pear, Opuntia macrocentra, Cactaceae

2012-05-01T21:35:00.002+01:00

A large prickly pear cactus, like this Opuntia macrocentra that comes from the Pecos region of Texas, is a thing of beauty when in full flower - although those long sharp spines can also inflict acute pain.

These magnificent flowers only last for a day and change colour to a more orange hue after pollination, which is apparently performed by bees. You can read an account of the pollination ecology of the plant here.

The fruits that form after pollination are edible in some species of Opuntia, notably O. ficus-indica, and marketed commercially as tunas that are popular in Mexico and occasionally appear on British supermarket shelves.

The stamens shed pollen soon after the flowers open in the morning but the stigma only becomes receptive in the afternoon and must be cross pollinated with pollen from a different individual plant before the flower will set seeds. The stamens are touch-sensitive, curling towards the stigma if you give them a gentle poke, mimicking the action of a visiting bee.

Flattened, jointed, photosynthetic stems called cladodes take over the function of leaves in prickly pears and most species defend themselves with long, sharp spines against grazing animals. These often have clusters of tiny, barbed hairs called glochids around their base and these are acutely irritating if the stick in soft flesh - like lips, for example. In a few species, like ...

...... this O.rufida the long spines are entirely replaced by vast numbers of glochids arranged in dense clusters called areoles. The glochids are ....

... easily detached and break off at the slightest touch, so gently brushing against one of these glochid-covered cladodes can be a very unpleasant experience. For a really close look at these nasty microscopic harpoons, click here.

Both species illustrated here are growing in the desert house in Durham University Botanic Garden.

Magnolia stellata, Magnoliaceae

2012-03-30T21:35:00.002+01:00

If we had enough space in our back garden I would plant one of the large flowered, tree-sized Magnolia species or hybrids - probably M. x soulangeana - but we only have room for the Star Magnolia, M. stellata which comes from Japan and produces many fine flowers on a relatively compact plant. It's the earliest-flowering magnolia and the weather here over the last week, which has been unremittingly warm and sunny, has been kind to the 15 year-old specimen in garden. In a couple more days it will be at its best, but four days from now temperatures are forecast to plummet, with maybe even some snow, so the current pristine display of flowers will probably suffer from some frost damage by the middle of next week and those pure white tepals will be scarred with brown patches.

Part of the pleasure from growing this plant comes from watching the attractive furry flower buds swell, bringing a growing sense of expectation. When the bud scales part and the pink tepals begin to force their way out, you know that spring is gathering pace.......... but anticipation is tempered by the knowledge that spring can be fickle. It looks like this year's display of starry flowers will be short-lived...... but spectacular while it lasts.

Garden Seats

2012-03-25T12:02:00.000+01:00

Long ago I promised myself that the next garden I have will be designed around the seating. Before I do anything else I'll identify the places that provide the best morning, afternoon and evening viewpoints and choose some comfortable seats where I'll be able to rest my weary limbs and admire my handiwork over a glass (or two) of wine. But generally speaking garden seating tends to be designed for looking at rather than sitting on and is often excruciatingly uncomfortable, unless you carry a pile of cushions around with you. Here are four attractive seats that are fine for a Digital Botanic Garden, but not much good for sitting on for any length of time.

Edwardian cast iron fern seat - lovely to look at but cold and very uncomfortable...

... lichen covered bench - obviously the gardener here was always far too busy to sit down.....but the seat really adds character and maturity to a garden....

.... follow the sun - wheel this one around your extensive acres in search of the best place to linger ... but not for too long on its hard wooden surfaces...

.... and a painfully intricate creation in cast iron, in a sun-trap surrounded by Caenothus and Wistaria....

Azara microphylla, Box-leaved azara, Salicaceae

2012-03-20T09:46:00.003Z

For most of the year Azara microphylla isn't a very impressive plant - just a rather straggly shrub with masses of small, glossy leaves - but for a couple of weeks in spring it reveals a rather delicious attribute: a powerful aroma of chocolate. It produces clusters of small golden stamens from the beginning of March onwards and when I opened our back door this morning (which is the day of the vernal equinox - the first day of spring) I was greeted by the chocolate scent that the Azara that's trained against the wall was releasing in the early morning sun.

The precise perception of scent is a personal attribute and I know some people who find that, to them, it smells of chocolate. Scents are often closely interwoven with memory and to me the aroma is reminiscent of the smell of a brand of chocolate called Caramac that I was very partial to in my youth.

If you are a chocoholic gardener you can find information on cultivating Azara, which can become a small tree, here and you can find more photographs here. Sadly the web is useless for conveying scents but if you can locate a bar of Caramac you'll see what I mean about the aroma .....

It is a native of Chile.

Rhododendron dauricum, Ericaceae

2012-03-16T17:30:00.002Z

I'm not a great fan of some of the overblown garden hybrid Rhododendrons but Rhododendron dauricum is always a welcome sight. It's an early bloomer - not surprising when you look at its natural geographical distribution, across northern Russia, China and Japan - and it has been flowering in my garden since the beginning of March.

The fact that it flowers on almost bare twigs enhances its beauty and no doubt ...

.... makes it more conspicuous to the first queen bees that emerge in spring from hibernation to collect nectar from the flowers. This Rhododendron species and many others in the genus have a particularly unusual way of dispensing pollen to visiting insects.

In many plants the anthers at the tip of the stamens simply burst open and expose all their pollen at once, but R.dauricum anthers dehisce through a small pore at the tip - which you can see clearly in the lower-most anther in this picture. The buzz of bees visiting the flowers makes the stamen filaments vibrate with a similarly high frequency, shaking pollen out of the pore a little at a time - which is an economical way of distributing the available pollen to as many bumblebee visitors as possible during the long flowering period in spring.

Congo Cockatoo, Impatiens niamniamensis,Balsaminaceae

2012-03-10T17:30:00.002Z

Flowers don't come much gaudier than this - primary colours straight out of a child's paintbox. It reminds me of some of the more lurid boiled sweets I used to buy in the sweetshop on my way home from school.

Impatiens niamniamensis comes from tropical Africa, from montane regions of Cameroon, extending through central and East Africa where it's used medicinally to treat migraines and painful joints. It makes a spectacular house plant, with one significant drawback - it seems to be extremely susceptible to pests like whitefly and red spider. The only way I've been able to cultivate it for any length of time without it resembling the contents of Pandora's box is to frequently root new plants from clean cuttings.

The flower has a very long, curled nectar spur and I've found a few sources that suggest that it's pollinated by birds - bright red flowers are often associated with bird pollination.

A big specimen in full flower makes a fine spectacle, resembling a tree full of parrots. There was a time, when I set out in gardening, when I was primarily interested in species with subtle, muted colours but these days I'm increasingly drawn to flowers whose colours are so hot you could warm your hands on them; maybe it's a symptom of advancing years..........

Woad, Isatis tinctoria, Brassicaceae

2012-03-06T15:39:00.000Z

About twenty years ago I fancied trying my hand at dyeing ..... and where better to start than with indigo extracted from woad? The woad seeds germinated well, the plants (which are biennial) flourished but somewhere along the line I lost enthusiasm for the enterprise - perhaps when I realised how much woad I'd need to grow to produce a worthwhile amount of dye and what a messy business it would be. You can find a description of the whole process here.

So the plants ran to seed, after producing a spectacular display of small flowers that were very popular with hoverflies. Even today, two decades later, occasional seedlings from those original plants appear in the garden so my redundant woad crop must have left a persistent seed bank.

Woad has been used as a source of blue dye since ancient times (for a detailed account click here) but was superseded by true indigo Indigofera tinctoria which in turn was replaced by modern synthetic indigo dyes.

Fritillaria michailovskyi, Liliaceae

2012-02-15T15:19:00.001Z

There are over 100 species of Fritillaria and I think this one, F. michailovski, was the first I ever encountered, in the alpine house at the RHS Garden at Wisley, about 50 years ago. There was something about the weird colour combination and art deco lampshade form of the flowers that really appealed to me but it was another 40 years before I got around to growing it for myself. These days the bulbs are more easily available and considerably cheaper than they were half a century ago. The species comes from the high mountains of North East Turkey and performs best if it's grown in an alpine house, in a pan of free draining compost topped with grit.

F. michailovskyi is one of the smaller species in the genus and this is the largest, the well-known, 1.5m. tall crown imperial F. imperialis, whose regal appearance is somewhat undermined by its unpleasant foxy smell. This unfortunate aroma may be the source of the belief that the plant repels mice and moles, that presumably think they are in the presence of a sharpd-toothed predator when they smell the plant. There does seem to be some evidence that the plant repels deer, that reputedly avoid it, and some recent biochemical analysis of the plant's nectar has identified the evil-smelling compound responsible as 3-methyl-2-butene-1-thiol, which I imagine could be the basis for a deer repellent if the effect is as strong as some people claim. Crown imperials grow wild in Turkey, Iran, Afghanistan and Kashmir.

William Robinson, in his celebrated The English Flower Garden, commented that most fritillaries have "dull tinted curiously interesting flowers" and that is particularly true of F.camschatcensis from Japan, Kamchatka and Eastern Siberia. In some forms of this plant the flowers are almost black but their other striking feature is a stench that is said to be truly disgusting. It's a plant for humus-rich soil in light woodland shade. Apparently the bulb is edible and is said to taste like roast chestnuts but I wouldn't be tempted to risk it since several Fritillaria species are known to contain physiologically active substances or are downright poisonous, including ....

... the familiar snake's head fritillary, F. meleagris. Like all fritillaries that I have ever grown this is an extravagant producer of nectar and is very popular with bumblebees when it flowers in my garden in late April. I've been growing it for about 20 years and it now seeds itself around the garden, often in unexpected places, but one of the best ways to grow it is in grass, as William Robinson recommended back in 1883: "It grows freely in grass not mown early", he wrote," and is therefore admirable for the wild garden; its various forms are amongst the most beautiful inhabitants of the hardy bulb garden, and tufts of the chequered or white-flowered variety are amongst the most graceful plants in cottage gardens".

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)