Biological battles in the glasshouses

Posted on by andy.winfield

By Helen Roberts and Nicola Temple


In the calm and serenity of the glasshouses, among the flowering lotus and breathtaking orchids, there is a lethal battle going on – biological warfare between predator and prey. About two months ago, Penny started to use biological control in the glasshouses as a chemical-free means of managing pests like whitefly and aphids. Parasitic wasps and beetles are released in areas of infestation and left to do what comes naturally to them…prey upon pests.
Biological control is a system that has been used by horticulturalists since the early 1800s. The University of Bristol Botanic Garden uses biological controls as it avoids the use of toxic chemicals and also controls pests that have become resistant to pesticide treatment. The method is more economical and certainly more environmentally friendly.
However, it’s not just entirely a simple matter of releasing the predators and then forgetting about it. First, the pests in the greenhouse need to be properly identified and the proper predator controls selected. Then, it’s necessary to release the controls under the right conditions and at a critical time of the season – known as inoculative release – in order for the control to be effective.

A grizzly end for aphids

Aphids have infiltrated the glasshouses at the Botanic Garden.


The Botanic Garden is using two species of parasitic wasps to control a range of aphid species. The story is a grizzly one for the aphid (think the infamous dinner scene in the movie Alien), but with an excellent outcome for plants in the long run! Female Aphidius colemanii and Aphidius ervi seek out their aphid hosts and with incredible precision pierce the aphid’s exoskeleton with their ovipositor and lay an egg directly into the aphid. After a couple of days the aphid dies as it is consumed from the inside by the newly hatched wasp larvae. The larvae then spin a cocoon around the aphid shell and an adult parasitic wasp eventually emerges. These wasps will also control insecticide resistant strains of aphids. Of the two species, A. ervihas a longer life cycle, is larger and will select larger hosts.

The Aphidiusspecies used at the Garden are released as newly emerged adults and are best released when temperatures in the glasshouse are between 15oC to 30oC.

Wiping out whitefly

Encarsia formosa is released on little
discs infused with parasitised scales.
To control whitefly, the Botanic Garden team are using two minute parasitic wasp species, Encarsia formosa and Eretmocerus eremicus. Encarsia formosa controls whitefly populations in much the same way as the parasitic wasps of aphids except they target the whitefly scale, which is the 2nd and 3rd nymph (immature) stage of whitefly, rather than the adult. Adult Encarsia will also feed directly on the whitefly scales. Female Encarsia can lay up to 200 eggs and only a single egg is needed to kill the whitefly. The parasitoids are sold as black parasitised scales that have been fixed onto cards and these are hung under the canopy of the greenhouse plants out of direct sunlight.
Eretmocerus eremicus is slightly different in its approach in that it lays its egg between the whitefly nymph and the leaf surface. Between the 2ndand 4th nymph stage, whitefly are sessile, and so when the egg hatches after 4 days, the wasp larva attaches its hook-like mouthparts to the underside of the whitefly scale and starts to chew. After about 4 days of chewing, the parasitoid larva crawls into the body of the whitefly scale and just sits there biding its time until the whitefly starts to pupate. When the pupation phase begins, the parasitoid releases enzymes that begin to digest the insides of the whitefly and this will be the wasp larva’s last meal before it begins its transition to adulthood – a process that takes about 12 days. The adult wasp chews its way out of the remains of the whitefly scale and the cycle begins all over again.

Making meals of mealy bugs

Cryptolaemus montrouzieri is a small ladybird species that is used in the control of mealy bug. Its larval stage looks like the mealy bugs they prey on, which is a case of aggressive mimicry. Eggs are laid in amongst the cottony egg sacks of mealy bugs and the eggs hatch after 5 days. The three larval stages of the beetle and the adults will feed on mealybug eggs, young crawlers, and the honeydew produced by mealybugs.
Adults are released onto infested plants in the evening and can be encouraged to stay in an area by using netting. These predators will also eat aphids and other scale insects if their prey of choice is in short supply.

Not all biological warfare goes to plan


As previously mentioned, the use of biological controls has many advantages, including reduced costs, reduced dependence on harmful chemicals and reduced potential for pests developing pesticide resistance. However, human interference in the predator-prey relationship doesn’t always go to plan.

One famous example is the introduction of the cane toad to Australia. These were introduced in 1935 to control the Greyback cane beetle that was destroying sugar cane crops. Essentially not enough was known about the cane toad and how it interacted with the target beetle; the two species are not compatible at all in terms of a predator-prey relationship. The beetle feeds at the top of the sugar cane stalks but the cane toad can neither climb nor fly and therefore cannot reach the beetle. The toad moved in to other areas besides sugar cane and spread like wild fire. They are productive breeders, which combined with a lack of predators due to their high toxicity, led to a population explosion. Its feeding habits are highly non-specific – it will just about eat anything that it can stuff into its mouth. Their introduction, despite the best of intentions, was an unmitigated disaster. This was one example that showed just how wrong biological control can go if not researched thoroughly.
However, rest assured the Botanic Garden will not be releasing anything but well-researched and proven beneficial insects into the glasshouses. When done properly, biological control is a highly effective strategy for managing pests.

Is there a role for plant-based medicine in our modern society?

Posted on by andy.winfield

What is the first image that comes to mind when you read the words “plant-based medicine”? This is the question James Wong presented the audience with last Thursday night at the 5th annual Annals of Botany Lecture held at the University of Bristol.
The audience, admittedly filled with plant aficionados, came up with answers such as aspirin and morphine. However, the same question posed during a university course that Wong teaches came up with some different imagery: dread locks and muddy boots, fads and big business, witch doctors in the Amazon, and cauldrons and concoctions. Imagery that suggests that plant-based medicine is a system of health care that is impractical, ineffective and therefore irrelevant. Given these cultural perceptions, is there still a role for plant-based medicine in an age where we are constructing nanoparticlesand running quantum algorithms?
Wong spent well over an hour exploring this question with an audience of over 200 last week – dispelling many of the myths that surround herbal medicine and distinguishing between scientific fact and cultural belief. But before I get to that, let me tell you a little bit about the man himself.

A self-proclaimed botany geek

If you’re not already familiar with the infectious smile of James Wong and his unbridled enthusiasm, let me introduce you. James is an ethnobotanist. He studies the relationships between plants and people – how people use plants, how they learn about what plants do, and how plants are perceived across societies.  He trained at Kew Gardens and his own research into traditional medical systems has taken him to Ecuador, Southern Chile and Indonesia.
You may recognise James from the award-winning BBC Two series Grow Your Own Drugs and as a member of the BBC One Countryfileteam. If that’s not enough, he’s also an award-winning garden designer and best-selling author. His energy level makes me think that he may have a very thorough understanding of some of the stimulant properties of plants, but as I’m working my way through my fourth cup of tea this morning, who am I to talk!

Drawing a thick black line between conventional and herbal medicine

James puts up a picture of a pile of pills on the left hand side of the screen and a picture of herbs on the right. These represent conventional and herbal medicine accordingly. James then uses some very opposing language to describe perceptions about these two schools of medicine – synthetic vs natural, evidence-based vs ineffective, proven safe vs potentially dangerous. Then, he draws a thick black line between the two.
“In the western world,” says James, “people in one camp immediately dismiss the other camp. But this idea is not scientifically based, it’s a cultural perception. Most scientists don’t see this black line. They are concerned about the efficacy of a substance rather than the source.”
For starters, many pills are derived from plants. In fact, 50% of the most commonly used conventional drugs and 75% of current cancer treatments are derived from natural sources. James provides a couple of fantastic examples:
·         Houttuynia cordata – is given as an injection treatment- known as HCI –as a treatment for severe acute respiratory syndrome (SARS) because of its anti-inflammatory properties.
·         Artemisinin is isolated from the plant Artemisia annua, sweet wormwood, and is taken as an antimalarial, replacing many of the quinine-based antimalarials.
So why is it that with so many medicines combating some of the toughest diseases of the 21st century coming from natural sources, there is still a perception that herbal medicines are best left for those that dance barefoot in the mud at Glastonbury?

Myth 1: Herbal medicines are ineffective

Reason 1: lack of evidence

The number one reason that herbal medicines are thought to be ineffective is due to a lack of evidence. James sites cost as the main reason that evidence lacks for these herbal remedies. With an estimated 50,000 medicinal plant species on the planet, James estimates that it would cost between USD $4.5 trillion and 36 trillion to test all these potential plant species (assuming we’ve actually found them) for the 300 most common ailments. This is 81 years of the world’s combined GDP. Not only is this unrealistic, there is very little economic incentive to even try to test all medicinal plants as patenting plant sources is very difficult.
The other challenge with providing evidence for the effectiveness of herbal medicines is that much of the testing is, quite frankly, inaccurate. James uses Echinaceaas a classic example of this. In a study looking at the efficacy of Echinacea, they tested the dried leaves and flowers of E. purpurea – the common garden species. However, it is the fresh root of E. pallida and E. angustifolia that is used in traditional medicines.
“This is like testing the fur of a kitten to determine the effectiveness of the claws of a tiger,” says James.
James also referred to a paradigm mismatch as the root of these perceptions.   We are products of our paradigm environments. You and I fully understand the concept of germs because we were raised in that paradigm. However, think about someone from an isolated tribe in the Amazon grappling with the idea that we have little creatures living on and in us that grow and multiply simply by dividing in two and can make us sick. It’s simply not plausible to them!
Morning glory seeds mashed up have mind-altering effects. It was once mainstream to use this powerful hallucinogen during psychoanalysis. The patient, in an altered state, would talk about issues that would otherwise be suppressed and then the psychoanalyst would be able to help interpret these ramblings and resolve the patient’s problems. In Latin America, the seeds are used in much the same way, except replace the psychoanalyst with a shaman and the mind-altered state is an opportunity to seek advice from spirit guides; same medicinal plant, but two very different paradigms.
We also seem to forget that the food we put in our mouth is, indeed, medicine. The prunes I gave my son yesterday…very effective…and I don’t need three clinical trials to confirm that!

Reason 2: loss of traditional medical knowledge

The second main reason for the myth that herbal medicines are ineffective is that there has been an incredible loss of traditional medical knowledge. When the Spaniards arrived, they brought with them disease that wiped out 70% of the indigenous people of what is now Ecuador and with this, much of the traditional knowledge.
Along with disease, the European visitors carried exotic seed that thrived in the new habitat that they created as they deforested the land.  Today, 90% of medicinal plants in Ecuador are hedgerow species from Spain. The indigenous people had to learn about the uses of these new plants that were now far more convenient than the small isolated populations of their traditional medicinal plants. It was then the knowledge of these new exotic species that was passed down to the next generations.

Reason 3: many herbal medicines simply do not work

Sadly, a few bad seeds with some overly-stated advertising can ruin it for an entire industry. James uses the anti-oxidant powers of pomegranates as an example. Yes, pomegranate does have relatively high levels of anti-oxidants, but in fact, no more than say an apple.

Myth 2: Herbal medicines are impractical

At this point, James returned the discussion back to food and how everything we eat has some biological effect on our bodies…those four cups of tea I had this morning certainly have! Lunch, for example, might include a curry, a couple of fig bars, a piece of chocolate and a cup of coffee.  In our body, this breaks down to antiseptic (onion) and decongestant (chili) in the curry, laxative (fig) in the fig bars, psychoactive (chocolate), and stimulant (caffeine). I don’t know about you, but eating has never been an impractical task for me!
To address this public perception of impracticality, many companies have packaged herbal medicines up in sterile looking ways in order to give the appearance of being synthesised drugs. A brand of IBS relief capsules, for example, is no more than a peppermint jelly when the ingredients are examined. An analgesic cream is simply refined capsaicin taken from chilies.
So, does herbal medicine still have a role to play in our age of information and technology?
“It does still have a role to play,” says James, “because we still eat and because we still use plants as the base for many of the drugs in use.”
In fact, James claims that the UK is now the world’s biggest grower of daffodils. The flowers aren’t for display purposes, they are grown for a stress hormone they produce known as galanthamine. The drug is very effective in the treatment of the symptoms of Alzheimer’s. The soil conditions in Wales are apparently ideal for stressing these lovely spring flowers into producing the hormone in abundance!
James’ final thought of the evening was that it’s not really a matter of whether herbal medicine still has a role to play, “it’s a matter of whether you wish to accept it.”
If you have an opportunity to listen to James Wong speak, I highly recommend it. He is both entertaining and educational .
A reminder that Sunday May 19th is Fascination of Plants Day at the Botanic Garden. There will be interactive displays, a plant hunt and garden tours running from 10am to 4:30pm. Find out more at the garden’s events page http://www.bristol.ac.uk/botanic-garden/events/2013/84.html. 

Weaving Ethel: How the Botanic Garden is bringing moas back to life

Posted on by andy.winfield

Last week I met Ethel. I’m not sure what image that name conjures up for you – perhaps it is the gutsy singer Ethel Merman or the eccentric EastEnders character Ethel Skinner. For me, I immediately think of Lucille Ball’s sidekick character Ethel Mertz in the old American sitcom I Love Lucy. It seems that Ethel is one of those names that summons a big personality, and the Botanic Garden’s Ethel is no exception. Of course, this might be due in part to her impressive stature at nearly 8 feet in height.

Ethel is a new willow sculpture currently under construction at the Botanic Garden. She is the first of two moa birds that will be on display among the native New Zealand plants in the garden. Despite her towering height, Ethel is going to be the smaller of the two birds, with the other giant expected to stand closer to 12 feet tall. The sculpture was named by her creator, Sally Meadows, who has been working two days a week on the ambitious project since February.

“Ethel had to be a female,” explains Sally, “because the female moas were much bigger than the males. It’s one of the biggest size differences known among bird species.”

Ethel is the first of two moa bird willow sculptures to
be displayed at the Botanic Garden later this year.


The plight of the moa

Moas are an extinct group of flightless birds that were endemic to New Zealand until they were driven to extinction. There were nine species all together, and the largest of the species, Dinornis robustus and Dinornis novaezelandiae, could reach heights of 12 ft and are estimated to have weighed around 500 lb.

Artist renditions of the birds look very similar to an emu, with feathers that have evolved to look more like fur, broad feet and sturdy legs built for running, and a long neck for browsing foliage. While originally it was thought that moas stood with very upright necks, much like emus and ostriches, a more complete analysis of their bone structure suggests that it was more likely that they held their heads in a more forward position.

The ancestral moa species was thought to arrive on New Zealand approximately 60 million years ago (Mya). A sparse fossil record prior to 6 Mya leaves many ambiguities about the early evolution of moa species. However, it is thought that numerous species had evolved on both the North and South Islands and then at around 22 Mya, during the Oligocene drowning, those inhabiting the North Island went extinct as the land mass was below sea level. Those on the South Island took refuge on the land that remained above sea level (only about 18% of the current land mass of New Zealand) and then are thought to have recolonised the North Island again about two million years later.

Prior to the arrival of humans, the moa’s only known predator was the Haast’s Eagle, which had a wingspan that was just shy of 10 ft and weighed a notable 33 lbs. However, as a result of hunting, habitat loss and a slow population regeneration time, all species of moa were driven to extinction by the first Polynesian settlers, ancestors of the Māori, by around 1400 AD.

The tall tree with foliage only at the
top is mature lancewood (Pseudopanax
crassifolius) – the immature plant can
be seen in the lower right corner.

Plants adapt to the selective pressures of tall grazing moas

Moas were grazing herbivores and analysis of the beaks suggests they were likely very effective ones; Pachyornis elephantopusis thought to have been able to slice through 8mm diameter twigs with its secateurs-like beak.
However, one native New Zealand plant that evolved significant defences against these grazers is the horoeka or lancewood (Pseudopanax crassifolius). For the first 20 years or so of its life, this tree has a series of very long, narrow, leathery leaves that have a very prominent central vein and serrated edges.  The leaves come off the narrow spindly stem and point downwards, which essentially resembles a spindly palm tree with knives pointing out in all directions. I imagine this would not be a herbivore’s first choice, even with secateurs for a beak.

Yet, as the plant matures it begins to transform its shape and appearance entirely. The lancewood eventually begins to form branches at the top and the new leaves lose their serrated edges and become wider and shorter. The hypothesis is that this species coevolved with the moa and once the plant surpassed the height of these grazers it shifted its strategy from a moa defense to a photosynthesizing offense; broader leaves on branches would be far better at harnessing the sun’s energy than the narrow downward facing leaves it had earlier in its life.
The immature lancewood has evolved
highly unpalatable leaves.

Ethel’s taller sister will eventually stand majestically near the Botanic Garden’s lancewood trees – a wonderful memory of an evolutionary arms race.

So how does one weave an 8’ tall moa out of willow?

When Sally shows me into the potting shed, Ethel is dramatically suspended by a number of ropes from the rafters. This enables Sally to move her up and down to work on different parts and to lift her out of the way if the gardeners need the extra space. However, with her head and neck complete, most of her body frame in place, and some temporary legs for stability, she is becoming increasingly less mobile.

Sally had taken a weekend willow weaving course at the Botanic Garden and had helped Vicky, a Botanical Horticulturist, do some demonstrations at last year’s sculpture exhibition in the garden. So, when she realised she was going to be made redundant in her job, she spoke to the garden’s curator, Nick Wray, about helping out with the moa project. The next thing she knew she was in charge of weaving the giant bird.

“I like doing creative things,” said Sally, “and my work in the past hasn’t offered me this.”

At the core of the sculpture is chicken wire that runs through the body and up the neck to provide extra strength. The overall 3D shape of the sculpture is due to a frame of different sized willow rings. The rings are then joined together by lengths of willow that are woven through the circles to give longitudinal support as well as provide a framework for weaving the outside.

Sally gets the willow from Somerset in bundles that are about five feet in length. The willow needs to be

Sally’s hands work swiftly as she weaves Ethel’s
willow body.

soaked for roughly a day per foot of length. It then needs to be given a couple of days to dry before it can be worked with.


Sally takes a length of willow and clips off a few inches at both the thick end as well as the spindly end. She then runs the willow across her knee, where she is wearing kneepads, to improve the flexibility as well as test it.

“If it’s not properly soaked,” explains Sally, “it will break on my knee and I can either re-soak it or throw it out.”

After the branch has passed the knee test, Sally takes it and pushes it through the woven circular structures of the frame tying it off at one end. Sometimes she uses twist ties to temporarily hold parts together as she works the piece, but these are removed and it is only the winding of willow upon willow that holds the massive sculpture together in the end…oh, and a little chicken wire at the core.

Ethel’s head and neck detail is complete.

“In the end, you’re at the mercy of the willow”

Sally points to a spot on the jaw line of the completed head and admits it bothers her. I have no idea what spot she’s talking about because it all looks pretty amazing to me, but she goes on to talk about the fluidity of the art. She works from a plan, but admits that “in the end, you’re at the mercy of the willow”.

Well, she’s not complete yet, but I think Ethel will do her name proud.

Seeds of Change volunteers get down and dirty

Posted on by andy.winfield

Last month Alex and Rhiannon wrote about the ballast seed collection at the Botanic Garden and hinted at a new project, called “Seeds of Change: Growing a Living History of Bristol”. The Seeds of Change project provides Bristol schools and community groups with an opportunity to grow ballast seed gardens of their own and link the plants that they grow to the maritime history that is integral to Bristol’s heritage.
The partners on this project, the University of Bristol’s Centre for Public Engagement, Botanic Garden, andArnolfini have all been working hard on different aspects of the project to prepare for its launch, including developing creative workshops in partnership with artists and academics, building relationships with schools and community groups, sorting out the logistics of planting ballast seed gardens all over the city, and recruiting a troop of student volunteers to go out into the community and help build the gardens. The project is well underway and I recently joined the student volunteers on a training session at the Botanic Garden as they prepared to head out to the schools and community groups.
The day’s training covered everything from advice on how to draw out the many themes of the Seeds of Change project and managing enthusiastic school children to tips on turning soil. However, like all good training, there was a practical component that allowed the volunteers the opportunity to get their hands dirty and pick up some great tips from the staff at the Botanic Garden at the same time!

Avoiding the ‘Tom and Jerry’ style of tool storage

Botanic Garden Curator, Nick Wray
explains tool safety.
After a brief introduction to the day by Seeds of Change Coordinator Martha Crean, and Botanic Garden Curator Nick Wray, the volunteers were divided into two groups. I followed Nick’s group out to the vegetable patch where they were to practice preparing a bed and sowing seed.
After the volunteers put down their gardening tools and gathered around, Nick starts with some basic health and safety. He points to rakes left in what he refers to as the ‘Tom and Jerry’ style. I’m sure you can picture it – stand on the upturned teeth of the rake and the handle springs up to crack you in the nose in a perfectly choreographed slap-stick comedy sketch. Only it’s not slap-stick and it’s school children rather than a cartoon cat and mouse.
Nick masterfully divides and designates, showing how to handle groups by example and taking the volunteers through every step that they will need to do when they go out to their schools and community groups. The volunteers range in gardening experience and so Nick doesn’t miss a single detail, explaining how to handle the tools without breaking your back, how to prepare soil that has been turned and broken down to just the perfect particle size, and even how to clean your boots when you’re done.
There are also tips about keeping school children engaged and busy. After he uses the draw hoe to mark out a furrow in the ground that marks the border where they will be planting, Nick says, “Now, you and I can see that but a child won’t. They’ll step right over it.” As a mother, I can immediately see his point, but I wouldn’t have thought of it had he not mentioned it. He suggests that the volunteers keep the children busy by getting them to collect pebbles or sticks to lie in the furrow and mark out the planting bed. Simple, but an effective way of keeping everyone engaged with the project.
Nick even manages to work in discussions of evolution as he points out that most of the seed is dark against the soil in order to avoid predation. These are tidbits of information that I would be storing for later if I were one of the volunteers.

And in the potting shed…

Froggie works with Seeds of Change
volunteer Alex in the potting shed.

With Nick’s group all busy sowing seeds, I decide to head back to the potting shed to see what Froggie’s group is doing in the potting shed. I walk in and it’s very quiet and the volunteers are all very busy filling small pots with soil, placing the pots in large trays and using other pots to level the soil, then planting the seeds, watering and placing the trays outside.  I’ve unfortunately missed the instructional part.
Some of the community groups and schools won’t have garden space, and so they will instead be doing some container gardening with their ballast seeds. The volunteers will have to be prepared for both situations.

Student volunteers share an interest in gardening and children

For the volunteers, Seeds of Change offers a wonderful opportunity to be involved in a city wide project that ties gardening in with themes related to art, history and science, while also building their skill set and network for the future.
While there are many benefits on paper to volunteering, I decided to chat with a number of the volunteers to find out what really brought them away from their studies and research to play in the dirt on a sunny March day.
Seeds of Change volunteers sowing ballast seed in pots.

When I approached Camilla, a second year undergraduate student in Biological Sciences, she was busy breaking down clumps of dirt with a rake in the Garden’s vegetable patch. Camilla worked at the Botanic Garden last year and really enjoyed it, so when the email about the Seeds of Change opportunity hit her Inbox she embraced the opportunity, “I was looking for something to do outside of my studies, but still related,” said Camilla. “It’s a chance to give something back while still learning.”
On the way to the potting shed, I walked with two plant ecology PhD students who are also volunteering for the project. After joking that the project would be a good distraction from their research, they admitted that it was the idea of growing gardens with children that appealed to them.
In the potting shed, Alex, a History of Art student, was busy patting down soil in little pots to provide an even surface for sowing the seeds. Alex is thinking about going into teaching and found the aspect of working with children appealing, but also comes from a family of gardeners and in her words, “is quite used to messing about in the dirt”.
For others, like Nicola, another History of Art student, it was the prospect of making contacts and working with Arnolfini that drew her into the project.

Next steps for the volunteers

Seeds of Change volunteers turning soil, preparing for
when they will help schools and community groups plant
ballast seed gardens all over Bristol.
After the day of training at the Botanic Garden, the volunteers are going out to the site location that they’ve been assigned to with Kasha Smal , who is both a horticulturalist and former primary school teacher.  Kasha has helped produce a workshop program for the Seeds of Change project directed at years 4, 5 and 6 (keystage 2). The workshop includes a 30-minute activity as well as 30-minutes of thinking about the origins of the plants and places they might know as well as uses of the plants.  Kasha will then introduce the idea of planting the ballast seed garden and introduce the volunteer.  The volunteers will take the opportunity to assess what the garden situation is – pots versus a plot, well-worked soil versus needs some work, tools on hand.
After the introductory session, the volunteers will return to their groups on their own and plant the gardens.  Then, a few weeks later, they will do a follow-up session to see how things are getting on and maybe take the opportunity to talk more about the plants that have germinated and link them to the themes of the Seeds of Change project.

Ballast seed garden is only one strand of the project

The project is ambitious. Gardening is only one component of the project as each of these groups will also do a creative workshop alongside the ballast seed garden. There are three workshops to choose from and each one combines an artist and an academic working on some aspect of the Seeds of Change project. When Martha explained each of the workshops to me, the one that caught my attention investigates the sounds of plants and involves a sound artist as well as a scientist. The idea is to explore the sounds you hear when you put a microphone up to a plant and investigate the biological processes that underlie those sounds.  That is most certainly the subject of a future blog post!

There will be a website that will be associated with the Seeds of Change project, and each of the 16 ballast seed gardens being built around the city will have a page within that website with pictures and anecdotes documenting their experiences. I’ll be sure to follow how the project is progressing and report back with news of how the volunteers are getting on.

The Seeds of Change project is still in need of some volunteers, so if you’re interested, please contact Martha Crean at 0117 33 18313 or martha.crean@bristol.ac.uk.

The benefits of flowering early

Posted on by andy.winfield

Bristol was a swirl of snowflakes and blossoms earlier this week. Monday on my walk the cutting wind was relentless. Yet, despite my frozen nose and numb fingertips, I stopped to admire the many splashes of colour along my route – a street lined with blossom-laden plum trees, front gardens lined with daffodils, heather and crocuses, splashes of primulas and even some snow drops in the local woods. As my teeth chattered despite my thick down coat, I did marvel at these early spring bloomers that have clearly found it to their advantage to flower despite cold temperatures, relatively short days, and a paucity of pollinators. So, what exactly arethe advantages of being the first blossoms of spring?
A robin and crocuses, both soaking up some sunshine
on Thursday at the Botanic Garden.

Early woodland blossoms have access to more light

The first and perhaps most obvious advantage is that these early blossoms appear before the deciduous trees come into leaf, which gives them more access to light. Many of these early blossoms are naturally woodland flowers and so as soon as conditions become tolerable, these flowers put all of their energy into producing foliage and flowers before the forest canopy has formed. If successfully pollinated, the plant will produce a seed for dispersal. Then, as the forest floor becomes shaded by the trees above, the flower and foliage die back and any unused nutrients are returned into the roots or bulb. There will be no sign of these plants above ground for the rest of the year.
Though this may sound very much like a ‘get-up-and-go’ approach to flowering, the timing of when each species, and indeed each plant, flowers is incredibly complex and scientists have yet to figure out all the intricacies. It is affected by physical factors, such as soil nutrients, water, sunlight, day length and temperature, but it is also affected by biological factors, such as abundance of pollinators, herbivorous predators, seed dispersers and competition from other plants.  All of these factors may ultimately affect the reproductive success of the plant; flower too early and there may not be sufficient to set seed, but flower too late and the bird species that normally disperse the seed may have already migrated to over-wintering grounds.

There is less competition for pollinators

Though there are fewer pollinators about in early spring, there are also fewer blossoms to compete for their attentions. Insects that emerge in early spring or that forage throughout the winter, such as some bumblebee species, do not have a plethora of blossoms to choose from, so this increases the likelihood that the flowers that are out will get a visit.

There is more time for seed maturation

For some early season blossoms, such as fruit trees, there is an enormous investment in seed production, which takes time. The benefit in the end, of course, is a rather extravagant and often delicious means of dispersing seed great distances.

Early blossoms favour out-crossing  (Munguía-Rosas et al., 2011)

Fewer blossoms in early spring also mean that pollinators will travel greater distances between flowers. As a result, a flower may receive pollen from a more distant flower, which may be less similar genetically. It’s the floral equivalent of “bringing in new blood”, also known as out-crossing.  Perhaps the genetic material carried in that pollen encodes some increased resistance to frost or disease…or perhaps not. Most importantly, it is adding diversity to the population, which is the foundation for adaptation.
The crocuses in my front garden are in full bloom.

The evolution of early bloomers

There are not only differences in the time that plants flower between species, but also between populations of the same species and between plants of the same population. For example, the crocuses at the front of my garden, which have been exposed to more direct sunlight, are much further along than those in my back garden, which are shaded by a cedar hedge. This is a clear example of differences in the resources available in these two different growing environments.
However, consider a woodland covered with bluebells, what drives those first few bluebells to burst out before the others? It might be slight differences in their growing environments, but it is also in part a result of their genetic makeup. A sort of bluebell “aptitude” if you will that predisposes them to go to flower quickly – two separate bluebells, under the same growing conditions, may still flower at different times. Of course, it is therefore inevitable that those bluebells that are first to bloom will be pollinated by others that are in blossom, giving rise to new generations of early bloomers.
It might also be that environmental conditions are such that early bloomers are for some reason more successful in reproducing, perhaps because pollinators favour early bloomers (Munguia-Rosas et al., 2011). This will eventually drive the flowering time of entire populations earlier each season and over time this will become fixed within the genetic makeup of that population, in as few as three generations for some species (Galloway and Burgess, 2012).

Temperate plants tend to be more flexible with their flowering times

In temperate climates, there are much bigger differences in variables such as frost, temperature and day length across the landscape, between the seasons and between years. As a result, flowering plants in these regions exhibit tremendous variability in their flowering time – it is an adaptive flexibility that enables them to take advantage of the best growing conditions possible regardless of when they might happen (within reason of course).

If you’re going to be a risk-taker, be sure and have a plan B

Of course, many of these early spring blossoms have what could be considered a back-up plan. Snowdrops, crocuses, and daffodils are all capable of both sexual and asexual reproduction. So, if there is a prolonged heavy frost after these flowers have emerged or they are not successfully pollinated for any other reason during the season, then the bulbs will still form new small bulbs that are genetically identical to the parental bulbs. However, it is sexual production that brings genetic diversity to a population and this is what will allow a population to adapt to changing environmental conditions and resist disease.
There is a lovely clip herefrom the BBC’s Private Life of Plantson their website showing the progression of early blossoms as a British woodland bursts to life in the spring.
Well, I hope you are getting the opportunity to enjoy these early spring blossoms! Also, be sure to come out to the Botanic Garden over the Easter weekend to enjoy the Easter Sculpture Exhibition – amazing art, refreshments, and garden tours sounds like an ideal way to spend a weekend to me, I’m definitely going to be there!
Here are the references used above:
Galloway LF and Burgess KS. 2012. Artificial selection on flowering time: influence on reproductive phenology across natural light environments. Journal of Ecology 100: 852-861. http://www.cfbiodiv.org/userfiles/1111.pdf

Munguía-Rosas MA, Ollerton J, Parra-Tabla V, De-Nova JA. 2011. Meta-analysis of phenotypic selection on flowering phenology suggests that early flowering plants are favoured. Ecology Letters 14 (5):511-521.

Students set to tell the story behind the ballast seed collection

Posted on by andy.winfield

Guest post by Rhiannon Williams & Alex Learmont

The seeds of some plants can survive for many years lying dormant, waiting for improved environmental conditions to germinate. Seeds can withstand extreme drought or cold; some dry seeds can be stored at -150 degrees Celsius without harm, and still be induced to germinate!  Some seeds can be transported around the globe in the hulls of ships, immune to the storms and scurvy, only to one day be dumped on the banks of a foreign river, which may or may not provide the conditions it needs to grow and flourish.

We are biology students at the University of Bristol and for our dissertation we are creating interpretation boards for one of the Botanic Garden’s newer collections – the ballast seed collection. Our boards will be displayed at the Botanic Garden next to the ballast seed flower bed, which can be found near the glasshouses. This summer, once the flower bed has been planted up, it will be a joy to come and visit.

Alex Learmont and Rhiannon Williams are
preparing interpretation boards and
other materials on the ballast seed project
as part of their dissertation.
Our aim is to provide visitors of the gardens and the public with accessible and interesting information about the ballast seed project and the plants found within the collection. In addition to the interpretation boards, we are making A4 cards with information for each plant species and leaflets that will be available at the Garden and on tours of the floating garden at the harbourside. Visitors will even be able to scan QR codes placed beside some of the plants with their smartphones and access informative websites for some of the species. This collection is unique to the Botanic Garden and we’re looking forward to telling the remarkable story behind it.

The project began as part of the ‘Port City’ exhibition at the Arnolfini

The ‘Seeds of Change’ project is an on-going exploration of the ballast flora of European port cities by the artist Maria Thereza-Alves. Empty or lightly loaded ships carry low-value materials such as earth, stones and gravel, or sea water as ballast to weigh them down, giving improved manoeuvrability and stability. This ballast was emptied into the river Avon and onto ballast dumps that used to be present around Bristol. For centuries, exotic plant species have been transported to Bristol in the ballast of trading ships coming from countries all over the world.

The project began in 2007 as a part of the international Arnolfini exhibition entitled ‘Port City’ and was part of the London 2012 Festival. With the help of Botanic Garden curator Nick Wray, a list was composed of exotic plants found growing on ballast dumps throughout the UK, including the local port of Avonmouth. The full collection of these seeds was germinated in the University of Bristol Botanic Garden. Then with the support of the Arnolfini, the Botanic Garden and Bristol City Council, designer Gitta Gschwendtner used a condensed version of this collection to transform a disused grain barge on Bristol’s floating harbour into a ballast seed garden.

The floating garden can be viewed from Castle Park, but visitors can only reach it by boat. The next set of boat tours begin this spring. For a small fare, visitors can book onto them through the Arnolfini. Some of the tours focus particularly on the design and artistic concepts of the project whereas others are aimed more at those with a botanical interest. For example, last summer a micro-sound tour allowed visitors to listen to the sounds of plants growing.

Exotic plants reflect Bristol’s rich maritime history

The idea behind the project was to draw links between Bristol’s floral history and the social and economic history of Bristol’s trading past. Human dispersal of plants often follows routes of transportation, and the ballast of ships was a route into Bristol for invasive plant species. Some of the plants are native to the Mediterranean, West Asia, North Africa, and even South America. Ships would have been trading back and forth to these places over the past few hundred years. The plants in the collection convey a living history of Bristol’s rich maritime past.

Relatively few seeds in the ships ballast would have survived the long sea journeys, but some were able to germinate or lie dormant in the ballast dumps around Bristol for many years. In the late 1800s ballast became a more important aid to invasion when the new generation of metal ships changed from solid to liquid ballast. Ballast water can contain hundreds of species including bacterial, microbes, small invertebrates and seeds. Now, ballast is a major source of invasive species to port’s and in coastal freshwater and marine ecosystems. The International MaritimeOrganization (IMO) has developed a Convention aimed at preventing these harmful effects, this involves “Ballast water exchange”. The water taken up at the port of departure is replaced during the voyage with water from the deep sea. The organisms in the deep sea water are far less likely to survive when the water is discharged at the port of arrival, hence reducing the impact of invasive species in ballast water.

Most exotic seeds never establish themselves

In 1996, Williamson and Fitter proposed a ‘tens rule’. The rule states that only 10% of non-native species imported into a region will appear in the wild. Of these, only 10% will become established, and 10% of the establishing species may become invasive. Therefore, only 1 in a thousand imported species will cause problems.

An important message the ballast seed garden conveys is that most non-native flora does not become established or invasive. Even if the plants survived the long journey, the environment where they were unloaded from the ships (such as a ballast dump) was likely to be unsuitable for growth, or the number of plants of the same species was too small to result in a viable breeding population. However, some of the species on the ballast seed display are capable of survival and reproduction in the wild. Many of these naturalized species exist alongside British flora causing no obvious damage to habitats and ecosystems.  The Garden promotes the idea for multihorticulturalism: the view that migrations of species are natural and trying to stop them is futile.

New projects bring ‘Seeds of Change’ to schools and communities

During spring and summer 2013 a new project, “Seeds of Change: Growing a Living History of Bristol”, will provide the opportunity for Bristol schools and community groups to grow ballast seed gardens of their own. The project was set up by The University of Bristol Centre for Public Engagement and the Botanic Garden in partnership with the Arnolfini, and with funding provided by the Heritage Lottery Fund. Academics, artists and student volunteers from the university will be working together to lead a programme of activities and workshops exploring themes of history, botany and art; making the original themes of the “Seeds of Change” project exciting and accessible to school children and community groups.

For more information on the Heritage Lottery Funded schools and community programme you can visit the University website: http://www.bristol.ac.uk/public-engagement/events/seeds-of-change/or contact Martha Crean by email: martha.crean@bristol.ac.uk or phone: 0117 3318313.

Re-potting lotus ready for the new growing season

Posted on by andy.winfield

The lotus plant is a symbol of friendship, family, rejuvenation, hope, rebirth, fortune, purification and positivity. The rhizomes of the plant lie buried in the sludgy, smelly mud on the bottom of lakes and ponds. Rising up from the mud are the leaves and the strong stems, which come up through the water to support the heavily scented, beautiful flowers. This pattern of growth makes the lotus a very important and powerful symbol in Buddhism. It signifies the progress of the soul as the flower rises from the primeval mud of materialism, through the waters of experience, and into the bright sunshine of enlightenment (source). Though most water plants send blooms to the surface in this way, only the lotus flower sits up to one metre above the water’s surface, truly rising above it all (source).

Lotus are a primitive plant. The fossil record shows that 15 million years ago there were eight different species of lotus, which were later reduced to only two species – the Asian lotus (Nelumbo nucifera) and the American lotus (Nelumbo lutea). The spiritual, nutritional and medicinal importance of this plant in Chinese, Vietnamese and Indian cultures has made it the focus of extensive research and breeding programs. There are over 500 different cultivars of lotus in the world and the University of Bristol Botanic Garden has carefully chosen cultivars that show the range of flower forms and colours for its small collection.

Last week I met Penny Harms, Glasshouse Coordinator at the Botanic Garden, in the potting shed to see what she’s doing to prepare the Garden’s lotus collection for the next growing season. Penny and her team pulled the lotus plants out of the pond in October, where they have been sitting dormant in their pots ever since. Now, it’s time to give them some attention and get them ready to go back into the pond.

Penny is very careful when cleaning
the lotus rhizomes as any damage will
affect its growth.

Looking after Lotus

First, Penny tips the pots out, getting rid of all the old soil and gently collecting the lengths of rhizomes that wind around in circles within the pots. The rhizomes are then placed into plastic trays with lids that have holes to ensure they don’t get moldy. Over several days, Penny then sorts through each of the trays and pulls off any of last year’s rhizomes, which are brown and rotten compared with the cream-coloured healthy rhizomes.

“You have to be really careful,” explained Penny. “These are the growing shoots – this is a leaf here – so if you damage these, the plant won’t grow very well this year.”

Once the rhizomes have been cleaned they are potted up. Penny has prepared a special mix which is a loam-based potting mix to which she adds Bracken Down – a mixture of thoroughly composted bracken, bark and manure – and Osmocote – a controlled release fertilizer.

“Osmocote releases its nutrients over 18 months in a normal pot,” said Penny, “but because the pots are going into a really warm tropical environment, this will speed up considerably. It will release the nutrients over the summer, which is quite handy as these are quite hungry plants.”

Bonemeal is also added to the soil to give added support to the roots and chicken manure pellets are also added to provide more food. The lotus plants replenish themselves each year, so all of the rhizomes Penny showed me will be completely replaced by new growth this year. If the soil doesn’t have enough food and the temperature isn’t warm enough, the plants get weak and don’t really do anything.

“Last summer was quite poor,” said Penny “which meant there was less light and the glasshouse didn’t get as hot. We noticed that the quality of the rhizomes has gone down this year. I record the quality of the rhizomes when I pot them up and we’ve had some really strong rhizomes in the past. But this year, they don’t seem to have done anything – it’s as though they reached a growth plateau.”

Trays of lotus rhizomes. The tray on the left hasn’t had
the old material removed yet, but the one on the right has
been cleaned and is ready to be potted up.

Placing lotus by the poolside

After the lotus have been potted up into clean pots with all new soil, Penny will write new labels and bring them into the tropical house. The pots then stand in trays of water along the side of the pool. This keeps the soil constantly wetted and after about a week of being in 25oC temperatures, the plants come into growth.

Once the leaves are 3-4” high and there are enough of them that Penny knows the rhizomes are growing, she raises the water level of the pool and moves the pots down onto a lower edge along the pool. This keeps the pots submersed in the warmest upper layer of water.
For the final phase, the pots are moved into the main pool where they sit on top of a stack of mesh trays. The water level is raised again so that it covers the top of the pots, but this has to be timed as well with the growth of the giant water lilies (Victoria) that occupy the large planters in the pond.

“Then that’s it for spring and summer,” said Penny “and I have to just cross my fingers that they do their stuff and produce beautiful flowers.”

The many uses of lotus

The rhizomes of lotus are rich in sugar and starches and contain up to 2% protein. They are sliced and roasted, dried or pickled. For medicinal purposes the rhizome is made into a juice or steeped in a tea and taken topically or ingested to stop bleeding.
The disc-shaped leaves and stems are eaten raw or used to wrap other foods, such as rice, for cooking. Medicinally they are taken to clear fever.

The flower has many uses. The outer covering of the flower – the calyx – is used in medicine. The petals of the flower are eaten and the male stamens are used to flavour tea and also contain the fragrant essential oil, which is extremely coveted. Lotus oil is three times more expensive than gold weight for weight. The receptacle, which houses the female parts of the flower and eventually the seeds, is aged and used for medicinal purposes.

The young green seeds have up to 16% protein content and are considered quite a delicacy. They can also be ground into flour to make bread or used medicinally to stop incontinence and digestive problems. The green shoots from the seed – known as the plumule – can also be removed and used for medical purposes.

There’s a lot in a name

When you visit the lotus display in the tropical glasshouse, you will notice that each of the labels has a series of names. At the top is the latin name (e.g., Nelumbo nucifera), then beneath that is the Chinese name (e.g., Xiao Foushou) and the translation (e.g., Small Buddha’s hand). Finally, along the bottom of the label is a description of the flower type (e.g., pink cup lotus). Chinese lotus flowers range from pink to white and some are cream or with a hint of green, but there are no yellow flowers in the Chinese lotus species. Yellow flowered cultivars, originate from the American lotus lineage.

The Botanic Garden has recently ordered some new cultivars from China to expand their lotus collection, including a yellow-flowered cultivar of the American lotus.
Date holder: Mark the 19th of May in your calendars as the Botanic Garden will be hosting a Fascination of Plants Day event. 

An update on Victoria!

Posted on by andy.winfield

So much can change within a week at the Botanic Garden it can make your head spin. When I spoke to Penny about the giant water lily, she informed me that she wasn’t going to be trying to germinate Victoria seeds yet as they didn’t have the facilities. However, within a week, that has all changed. Penny received some seeds from Oxford and is currently putting together the pot and water heater she will need to keep the seeds at a balmy 30oC to germinate. Along with that, the Paignton Zoo has managed to overwinter a small plant, which is a Victoria Longwood hybrid that they are giving to the Botanic Garden along with some young germinated Victoria cruziana. Suddenly, Penny has gone from having no seeds to having seeds, young plants and old plants…it’s lily overload!

Preparing the pool for Victoria

Posted on by andy.winfield

Each year at the Botanic Garden, the pool in the tropical zone glasshouse is drained of two thirds of its water and prepared for a new growing season of water-dwellers. The most dramatic of these, is without a doubt, Victoria – the giant water lily. The enormous round leaves, spanning as much as six feet (~2m) across, provide a floating habitat for insects that crawl from leaf to leaf, while anacondas and piranha lurk in the waters beneath. Penny Harms is the Glasshouse Coordinator at the University of Bristol Botanic Garden and she spoke to me this week about what’s involved with providing these native South American giants with the best habitat possible in a northern temperate climate.
As we stood beside the pond chatting, the surface of the water was constantly dimpled as the guppies rose to the surface in search of a meal. The water level is very low, revealing two large wooden planters that sit empty.  The planter on the left, Penny tells me, will contain Victoria cruziana the Santa Cruz water lily – famous for its giant leaves with the strength to support small children.
In its native habitat, in the slow-moving backwaters of the Paraná Basin and in the Pantanal region, this giant lily grows as a perennial. However, here in the UK it is grown as an annual as the plant simply doesn’t tolerate the low light quality and short day length in winter, not to mention the low temperatures in the pool.
“It’s a large plant and very, very greedy,” explained Penny. “It grows at an incredible rate, so it’s easy to grow as an annual and most botanic gardens with tropical glasshouses that display this plant, do so over the summer months.”

Propagating Victoria

It is this time of year, in February, when the seeds of Victoria should be germinated. Propagators will keep the seed over the winter in distilled water and then sow them in small tropical tanks that Penny describes as “glorified washing-up bowls”, which are filled with a very rich loam.
“Really, you’re just trying to replicate what happens in the wild,” said Penny. “The seeds are scattered and are washed up along the edges of the river banks where they settle in very silty, very fine mud. They just sit there until the temperatures are perfect and then they germinate. So, you really don’t need to do much.”
Once the seeds germinate, the plants start growing quite fast. They will be planted out two or three times and when they’ve got two or three decent sized leaves and are in a 40cm pot or so, they are ready to be put into the pond planters. Penny prepares a special mix of soil for the planter that is predominantly loam-based, to which she adds well-rotted manure. She also adds a slow release fertilizer for these greedy plants, which will also be added every six weeks thereafter.
The water level in the tropical pond has been
dropped to expose the wooden planters that will soon
hold the giant water lilies.
The water level of the pond is then raised so that the leaves are resting on the surface and as the plant grows, the water level is raised again and again to accommodate the growing plant.
“Obviously in a pool this size we can’t let it get to the size it would in the wild,” said Penny, “so I remove about one or two leaves a week once it gets going. In this planter, the lily could have four or five leaves, all three to four feet across, but it would all get quite tangled. So instead I reduce it down to about three to four leaves allowing fewer leaves to stay on the plant longer and therefore get bigger.”
The leaves of V. cruzianaare a purplish red colour on the underside and have an impressive network of ribs that are lined with spines. It is thought that these spines offer protection from herbivores such as grazing fish and manatees. The leaves themselves can support up to 99lbs (45kg) of evenly distributed weight, which is facilitated by floatation provided by air that is trapped between the ribs on the underside of the leaf and its distinctive pie-dish rim.

Beetle trapping flowers of the night


Victoria cruziana starts producing flowers after about two months of growth. The flowers open only at night and cast a lovely pineapple smell out into the night air to attract pollinating beetles.
“It only flowers for two days,” said Penny. “The flower will open one late afternoon and be fully open over the night and then it will close during the day and open again a second night, and then that’s it. The little black beetles, which pollinate the flowers in the natural habitat, fly from flower to flower and often get trapped in the flowers when they close during the day.”
While beetle trapping may seem coincidental, it actually serves an important role in the pollination process. The first night that the flower opens it is white and it is its female reproductive parts that are mature and awaiting the pollen carried by the beetles attracted to its scent. However, when the flower is closed during the day it undergoes a sexual transformation and it is the male sexual parts – the pollen laden anthers – that mature. The flower also changes colour, from white to pink, during this process. The trapped beetles get covered in the flower’s pollen as they walk about their petal-walled cell. Then, when the flower opens on the second night, it releases the beetles, which will seek out a new fragrant white female flower. Essentially the plant has guaranteed its pollen delivery system by trapping it!
The glasshouses are definitely worth a visit right
now as the orchids are putting on a wonderful display.
Though the University of Bristol Botanic Garden hasn’t yet propagated its own Victoria cruziana, Penny hopes to do so in the future. Part of the challenge has simply been finding room in the already full propagation house. Proper heaters would also be required to maintain the temperatures needed to germinate the seed. For now, Penny and the horticultural students are already incredibly busy with the preparations needed to plant out the tropical pond.
“There is a lot to do and we have to get things done by a certain date,” said Penny, “because if things aren’t planted out by a certain time, their growing season is shortened. The later you put things in, the longer it takes them to get going and ultimately we want to have things ready for when the public comes in at Easter.”
The glasshouses are of course open to the public now and it’s a good opportunity to see work in progress and to also check out the orchids in the sub-tropical zone, which are putting on a lovely show right now!

The chemical allure of plants

Posted on by andy.winfield

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!