Category: Uncategorized

By Susan Stephens

According to a report by the Royal Botanic Gardens at Kew in 2016, there are around 391,000 species of plants in the world and around 94% of these are flowering plants. Plants are grouped in families based on their physical and genetic characteristics. One of the largest flowering plant families is the Orchidaceae, or Orchid family with around 28,000 species, so around 10% of all flowering plant species. Recent DNA research shows that at over 90 million years old, orchids are amongst the most ancient of the flowering plant families.

Orchids can be found throughout the world in every type of habitat and climatic zone apart from the

Coelygene cristata

very driest deserts and glaciers, and on every continent except Antarctica. The majority of orchids are found in the tropics of Asia, South America and Central America and new species are constantly being discovered, particularly in these areas. Their tiny, dust like seed that has enables orchids to disperse and travel great distances, carried on the wind across oceans and continents to colonise the world. The majority of these tropical and sub tropical orchids are epiphytes and grow anchored to trees. They are not parasitic and so do not feed upon the tree but absorb water and nutrients from the rain, air and other debris that collects nearby with the aid of their aerial roots; the tree to enables them to reach higher elevations and so have more access to sun and air. An example of epiphytes you can see in the Garden is the Dendrobium; Dendrobium, derives from the Greek dendron meaning tree and bios meaning life. It literally means “one who lives on trees” or essentially epiphyte.

Dactylorhiza fuchsii

Terrestrial orchids grow on the ground and can be found in places as diverse as the hot, dry Australian deserts to the shade of temperate woodlands. They are found in areas of Russia extending to the very edge of the Arctic Circle. All of the 52 or so species of orchid found in the UK are terrestrial orchids including Ophrys apifera (the bee orchid) and Dactylorhiza fuchsii (the common spotted orchid).

Lithophytes are somewhere between the epiphytes and terrestrials in that they make their homes on rocky cliff faces. They obtain their nutrients and water in a similar way to epiphytes relying upon regular mists and rain for moisture. Extra moisture is obtained from roots that meander and penetrate into the crevices in the rocks. Some species of Paphiopedilum and Pleiones are lithophytes.

Orchids use a wide range of inventive methods to attract pollinators. Most orchids rely on specific

Ophrys apifera, the bee orchid

pollinators and in most cases orchid and pollinator have evolved together. Nectar is the main reward to entice pollinators but also use of colour, shape, fragrance and sometimes mimicry is applied. Orchids attracting butterflies and hummingbirds are brightly coloured but not necessarily fragrant while orchids which wish to attract moths and night flying insects are usually white or green and very fragrant at night. The Bulbophyllum species of orchid are brown or fleshy red and are foul smelling to attract the flies which pollinate them. Some orchids deceive their pollinators by mimicking the appearance and scents produced by female insects. The male insect will attempt to mate with the false female and in the process, the orchid deposits pollen on the insects head which he carries to the next flower.

The orchid family is probably one of the most important plant families from a horticultural point of view and are grown for the amazing variety

and beauty of their flowers. Enthusiasts will pay thousands of pounds for a rare specimen. Otherwise, considering the size of the family, orchids have very few commercial uses. The only commercially important product

Vanilla planifolia

derived from orchids is vanilla which is used for flavouring foods, drinks and cosmetics. Most vanilla is produced from one species, Vanilla planifolia. The plant is a climbing vine form of orchid native to Central and South America. Vanilla production today is mainly in Madagascar which is the largest producer of vanilla beans. However the island lacks the plant’s pollinating bee species so the flowers must be hand pollinated.
The underground tubers of a terrestrial orchid, usually Orchis mascula (early purple orchid) are ground to a powder and used for cooking, such as in the hot beverage salep or in the Turkish frozen treat dondurma. Traditional Chinese medicine uses orchids extensively for combating various different ailments. Of the thousands of species of orchids known to us, about 50 orchid species are used in Chinese herbal medications.

Pleione formosiana

Here at the garden we have a large display of around 75 different species of orchids mainly in the sub tropical and tropical glasshouse. These include epiphytes such as Coelogyne and Dendrobiumspecies many of which are displayed on our fake but very realistic trees in an effort to replicate their natural habitats. There are also many terrestial orchids displayed in pots in the sub tropical glasshouse

including Stenoglottis longifolia with it’s spikes of many small, lilac, speckled flowers and Paphiopedilumspecies often known as slipper orchids because of it’s pouch like lip. The amazing twining vines of Vanilla planifolium can be found in the tropical glasshouse. Outside in the Chinese Herb Garden, terrestial orchid Pleione are displayed in the summer and the Dactylorhiza fuchsii can be seen growing beside the lake. Whatever time of year you visit the garden you will always find orchids in flower in the tropical and sub tropical glasshouses. Right now Coelogyne cristata, an epiphytic orchid from the cool monsoon forests of the Himalayas, is covered in cascades of brilliant white flowers with a bright yellow centre and wavy petals. It has rounded pseudobulbs and the light scent of jasmine. Another Coelogyne flowering in the sub tropical glasshouse at the moment is Coelogyne flaccida with it’s long racemes of creamy white flowers with yellow and brown markings. It has a sweet, light scent and cone shaped pseudobulbs which resemble bananas. The Dendrochilum glumaceum which is native to the Phillipines, is putting on a fantastic display with masses of long feathery pendulous spikes containing two rows of small pure white flowers with a yellow lip and smelling of sweet hay.

Dendrochilum glumaceum

Paphiopedalum

Hay scented orchid

Laelia anceps

By Andy Winfield

A goldfinch eating the seeds from a teasel plant.

Our efforts on the left, Oaxaca market stall on right. (right photo by Alejandro LinaresGarcia)

By Helen Roberts

Beachcombing is fun no matter what your age. Shells, pieces of driftwood and cloudy coloured glass somehow find a way into pockets, rucksack compartments and lunchboxes. A holiday to Slapton, in the South Hams, over the summer cemented our family’s curiosity in scouring the beaches. But whilst beachcombing, I was also similarly intrigued by the plants growing in this environment.

The coast here has a constantly shifting flora highly specialised for growing in difficult conditions. There is a shingle ridge that runs parallel to the shoreline, dividing the lake (Slapton Ley) from the sea. The plants that I discovered along the ridge path that runs northeast from the village of Torcross looked so intrinsically a part of the place, that to me they amplified the essence of this unique shingle coast.

All of the species on the shingle ridge have evolved ways of coping with difficult coastal conditions. The plants here are frequently subjected to saline spray and blown salts, high winds, exposure to hot summer temperatures and low soil humidity. The physical makeup of the shingle (it is a mix of flint, chert and quartz intermixed with some finer material) means that the substrate is very free draining and this results in the acute leaching of nutrients.

Thick leaves and deep roots

Most species that grow here have developed a cuticle (the protective film covering the leaf) that resists the entry of salt water or the leaves are sclerophyllous (thick, waxy and leathery). Often leaves are succulent and allow more effective retention of water.

Giant leaved sea kale (Crambe maritima) Photo credit: Peganum [via Flickr CC BY-SA 2.0]

White hairs on the leaf surface, which give a silvery hue, are also adaptive in preventing evaporation as they trap moisture, conserving water within their microclimate. The yellow horned-poppy (Glaucium flavum) has hairy sclerophyllous leaves. This is a toxic but striking perennial, with bright yellow flowers that later produce a stunning display of long horned seedpods. This plant has an extremely deep root system in order to access water deep down, but this also helps with stability during high winds.

Other plants on the shingle bar include the beautifully architectural rock samphire (Crithmum maritimum) and the giant leaved sea kale (Crambe maritima), the latter becoming popularised through its abundance in Derek Jarman’s extraordinary shingle garden near Dungeness. Sea kale taproots reach depths of up to 2 metres, providing them with a significant anchor in coastal winds.

Lying low

Restharrow (Ononis repens) is a common beach dweller. Photo credit: Matt Lavin [via Flickr CC BY-SA 2.0]

Some plants have adapted a slightly different approach to coastal living. They nestle down as low as they can and spread horizontally to reduce the amount of surface area exposed to the hammering winds. The small fleshy leaves of the sea campion (Silene uniflora) are closely packed and the plant grows in low mats. It is only the flowering branches, with their pretty white flowers and inflated bladders, much like calyx, that dare poke their heads up into the wind. Restharrow (Ononis repens) is an attractive low creeping aromatic herb with hairy stems and small pink pea-like flowers. The evaporation of essential oils released by aromatic plants is thought to cool the environment around the plant and thereby protect it from periods of extreme heat. Restharrow also has an extensive root system. Other species like chicory (Cichorium intybus), viper’s-bugloss (Echium vulgare), thrift (Armeria maritima), wild carrot (Daucus carota) and bird’s-foot-trefoil (Lotus corniculatus) all grow on the shingle ridge and are highly prized by pollinating insects.

These species have adapted to this environment. Although the ridge is only a narrow two metre strip of shingle, it displays a wonderful mosaic of disturbed ruderal* vegetation that forms a linear ribbon of interesting shapes, forms and flowers. Observing this particular plant habitat has helped me in the development of my own gravel garden at home. Some of these species are better suited to a garden environment and so I will begin with these. Although, more often than not it’s a matter of trial and error when trying to take plants outside of the conditions in which they thrive. Beth Chatto’s famous mantra, ‘Right plant, right place’ springs to mind and is always in my thoughts when I am planting my own garden or designing for other people.

*Ruderal is a term in botany that refers to plants that grow on waste ground or among rubbish.

 Helen Roberts is a trained landscape architect with a background in plant sciences. She is a probationary member of the Garden Media Guild and a regular contributor to the University of Bristol Botanic Garden blog.

We have all been drawn in by that scent carried on a spring breeze – something sweet or fruity, maybe even spicy or with a hint of citrus. If we’re lucky enough, we might even find the source and bury our noses among the petals in order to fill our head with the aroma. We, and ancient cultures before us, have been besotted by the chemical allure of plants.

Recently, I wrote about the ‘Scent of winter’ in the Botanic Garden and how winter blooming plants tend to be incredibly fragrant in order to attract pollinators at this time of year. I immediately wanted to dive into the science behind floral fragrances, but quickly learned that this was a discussion all on its own…perhaps even a tome.  

The scents associated with plants are produced by a mixture of chemical compounds known as volatile organic compounds (VOCs). They are described as volatile because they have a low boiling point, which means they are gases at room-temperature. It is these VOCs that are extracted as essential oils for aromatherapy or medicinal purposes, and that are carried on the wind in order to attract pollinators from long distances.

No two scents are the same

Due to the incredible variety of compounds and small differences in the relative abundances of these compounds, no two scents are exactly the same. In fact, insects are able to use these individualised scents to discriminate between individual flowers of a single species. This can be very important for pollinators as they can distinguish flowers that might offer a greater reward by having more nectar than others.

Scent is particularly important for plants that are pollinated by night-feeding animals like moths or bats, and it is also clearly important in winter when there are fewer pollinators about. Generally speaking, sweet smelling flowers tend to attract bees and flies, while strong musty, spicy or fruity odours attract beetles.

Specialised chemical cocktails

However, the chemical allure of plants is far more complex than just a sweet smell wafting on the breeze. Some species have become so incredibly specialised with their chemical cocktails, that they mimic the natural chemical signals of animals – pheromones – in order to attract pollinators.

One of the most successful groups of mimics is the orchids and within this group, perhaps the best known for their trickery are the bee orchids (Orphys). Not only have the flowers evolved petals that look like a female bee or wasp resting on the flower, the petals also give off an enticing scent that mimics the female’s pheromones. The male bees are lured in by the smell and “mate” with their deceptive petals, with nothing more to show for it than a dusting of pollen. The male will then carry the pollen to the next flower that tricks him.

Another orchid, Dendrobium sinense has a scent that mimics the honey bee alarm pheromone, which attracts hunting hornets as pollinators.

It’s not always about attracting pollinators…

Of course, the scent given off by plants isn’t always about attracting pollinators. Some plants use scent to attract predators and parasitoids of herbivorous insects. When the leaves of these plants are under attack by the herbivores, they will produce more VOCs, which not only bring in the predatory recruits, they also signal neighbouring plants to take action. For example, Lima beans (Phaseolus lunatus) will begin to secrete extrafloral nectar if a neighbouring Lima plant is under attack. This amplifies the call for help and attracts even more natural predators into the battle zone.

…and it’s not always a nice smell

I spent nearly 20 years on the west coast of Canada, the home of Lysichiton americanus. Anyone who has encountered the fragrance of this plant while walking in the wet coastal forests, knows where it gets its common name, skunk cabbage. The distinctive odour might be offensive to humans but for scavenging flies and beetles, which pollinate the plant, it signals the smell of something rotting and definitely worth investigation.

So, while I don’t recommend burying your nose in the flower of a skunk cabbage, it is definitely worth taking a moment to stop and smell the roses…just be sure a bee isn’t in there!