Month: February 2017

Sowing Victoria

Posted on by andy.winfield

By Nicola Temple

A photo taken a couple of years ago – I
have a grasp on my son as he leans
over into the tropical pool to get a
good look. Victoria cruziana is in flower
as is the lotus above us.
Photo credit: Shelby Temple

For me, one of the highlights at the University of Bristol Botanic Garden is the giant waterlily (Victoria cruziana) that lives in the pond in the tropical glass house. Its enormous leaves, which can reach 2 metres in diameter, are studded with spines on the underside and always provide ample wow factor for visiting children (my own included).  

The plant is found in slow moving waterways in Brazil, Argentina, Paraguay and Bolivia – in places such as the Pantanal. Its pollination story is an interesting one in that it is pollinated by a beetle (Cyclocephata castaneal). Its white flowers give off a strong scent that attracts the beetles in the evening. The flower then closes around the beetles, trapping them in the flower overnight. The flower produces heat (thermogenesis), raising the temperature as much as 9oC above the ambient temperature outside, which means the beetles can maintain a high level of activity without using as much energy. It’s a thermal reward and the plant benefits as the active beetles will pollinate the flower. The pollinated flower opens the next evening, revealing a new light pink colouration to its petals. The beetles flee the flower and make their way to the next unpollinated flower.

Of course, this species of beetle isn’t found in the Botanic Garden, which makes pollination a bit more challenging. However, there are other insects in the Garden that have filled this niche and the plants have set seed over the last few years. However, this is the first year that staff at the Botanic Garden have tried to sow this seed and, so far, things are going well!
The seeds of Victoria cruziana are kept wet.
Photo credit: Andy Winfield

Replicating the natural environment

In its natural environment, the seeds from Victoria cruziana would be buried in the sediments, stirred up perhaps by grazing capybara and swirling river currents. It wouldn’t be until the high water levels following the rainy season had receded that the water temperature and the amount of light penetrating to the sediments beneath would be sufficient to prompt germination.

In the Botanic Garden, botanical horticulturist, Andy Winfield, first primed the seeds by scratching the tough seed coat with secateurs. The seeds were then sown into topsoil and covered with a layer of horticultural grit. The pots with the sown seeds were then placed in a container of water to a level about 10 cm depth above the seed. This replicates the approximate water depth in the natural environment. The water is heated to a temperature of between 30oC and 32oC; this is critical to start the germination process.

Andy scores the seeds with secateurs
before sowing.
Photo credit: Nicola Rathbone

Victoria cruziana grows around the edges of water bodies and in wetland areas where there is no forest canopy. In order to replicate the amount of daily sun it would be receiving in the tropics and sub-tropics, grow lights on a 12h on/12h off cycle were hung above the pots. Then the whole contraption was covered in plastic film to reduce evaporation and maintain humidity.

Andy had read that germination time is generally about 2-3 weeks in this type of scenario, but within a few days he noticed that the seeds were starting to send out roots and when I visited a week after sowing, the hypocotyledonous stems were clearly emerging from the seeds and shooting upwards toward the surface of the water. 

Preparing to plant Victoria out

At the moment, the water temperature in the pool in the tropical glasshouse is only about 14oC, far too chilly for Victoria. In the coming weeks, however, these plants are

likely to grow quite quickly. Andy and the rest of the team at the Garden will pot them on several

times, gradually reducing their water temperature. At the same time, Bristol temperatures will be increasing and the tropical glasshouse will start getting warmer, as will the pool. By the time the Victoria plants have a few decent leaves, the temperatures between the tropical pool and the plants will have become similar enough that Victoria can be put into the planters in the pond.

The annual light intensity here in Bristol is considerably less than Victoria cruziana would receive in South America. However, the long summer days here mean that during those months more solar radiation is received here in a single day than in tropical South America. This helps Victoria cruziana flourish in the Botanic Garden tropical pool over the summer and it will be worth a visit to see it in flower. See the series of photos below taken the day the seeds were sown.

Andy prepares the loamy mix for sowing.
Photo credit: Nicola Rathbone

The seeds are sown into a loamy mix.
Photo credit: Nicola Rathbone

The soil is covered with a horticultural grit.
Photo credit: Nicola Rathbone

The seeds are sown and are ready for immersion
in a nice warm bath.
Photo credit: Andy Winfield
The pots immersed in the warm bath.
Photo credit: Nicola Temple
Only one week after sowing, the embryonic stem
has emerged and is stretching for the surface.
Photo credit: Nicola Temple

Sources:

Seymour, R.S. and Matthews, P.G.D. 2006. The role of thermogenesis in the pollination biology of the Amazon waterlily 
     Victoria amazonica. Annals of Botany 98(6): 1129-35.

A portrait of a boy and his plant

Posted on by andy.winfield

By Nicola Temple

On the 12th of February 1809, Charles Darwin was born in a large Georgian house, known as The Mount, in Shrewsbury. As a biologist, I am very familiar with the works of Darwin. And when I conjure an image of this man in my head it is of him in his 60s, bald on top and with a formidable beard. However, on a recent visit to the University of Bristol Botanic Garden, the curator, Nick Wray, showed me a portrait I had never seen before.

The portrait was completed in 1816, just before Darwin turned 7 years old and he is with his sister Catherine. It is a magnificent piece done using chalk on paper, by the artist Ellen Wallace Sharples (1769-1849), who was settled in Bristol at the time – not far from the Botanic Garden in Clifton [see note 1].

Nick pointed the portrait out to me because he is interested in the plant that Darwin is holding in the portrait. Children would have often been given something to hold while sitting for a portrait – it gave them something to do with their hands to prevent fidgeting. While Catherine has a posy of flowers in her hand, Charles is holding a clay pan on his knee with a plant in full bloom. This would have been no small feat for a child.

The portrait painted by Ellen Wallace Sharples in 1816
of Charles and Catherine Darwin.

Nick recognised the plant held by Darwin as almost certainly Lachenalia aloides (the opal flower), which is a native to the Western Cape of South Africa. Nick informed me that Cape flora were very in vogue during this period. The collecting activities and botanical observations of horticulturist-explorers, such as W. Paterson, Francis Masson, Robert Gordon, W.H.C. Lichtenstein, John Barrow and William Burchell, created a voracious appetite among Europeans for the curious plants of the Western Cape, while established trade routes enabled their transport back to Europe. So it is very likely that the children of a wealthy family would have been given such exotic pieces to hold rather than a favourite toy.

The artist almost certainly painted the portrait at the Darwin’s family home, The Mount. Records show that their impressive house had equally impressive gardens, including a conservatory and hothouse. The Lachenalia aloides likely came from one of their own glasshouses. Grown correctly in a cool frost free glasshouse, this little plant flowers from February-March. In a warm glasshouse it would flower earlier.

In an article written for the Garden History Society by Susan Campbell (Vol. 40, No 2 Winter 2012), she lists the plants cultivated at the Mount, including those growing in the Conservatory and Hothouse. In these lists, one species of Lachenalia is mentioned, Lachenalia pendula, which is now known as Lachenalia bulbifera. This species is almost always red in colour with the robust flower spike leaning to one side. However, yellow tipped orange forms have been recorded in the wild. Whether the plant in the portrait was misidentified in the original plant list or it was correct and an unusual orange and yellow form was cultivated, we shall never know. On examining the portrait carefully, its habit, erect inflorescence and the colour of the flowers, suggests the plant was wrongly identified and should be Lachenalia aloides. Nick goes onto suggest that, “the presence of this Cape bulb flowering in this portrait is evidence that the chalk picture was made around the 12 February 1816, Charles Darwin’s seventh birthday. The picture may have been commissioned deliberately to commemorate the occasion”.

About Lachenalia aloides

There are about 110 different species of Lachenalia, 80 of which are found in the Cape region of South Africa. L. aloides has a number of different varieties, all of which grow on granite or sandstone outcrops. The flowers can vary quite a bit in their colour. Some plants have flowers that are nearly entirely yellow, while others are magenta at the base turning yellow and then to green.

The Lachenalia genus are geophytes, which means that they spend part of the year dormant as a fleshy underground structure, such as a bulb, rhizome or tuber. South Africa is a global hotspot of geophyte diversity. There are 2,100 species across 20 different families in the area and 84% of them are endemic.

Lachenalia aloides is naturally pollinated by sunbirds, which use their long curved bill to access the nectar at the base of the tubular flowers. It was widely-thought until fairly recently that sunbird-pollinated plants had almost always evolved perch-like structures to make feeding for the sunbird easier. However, L. aloides has no such structure and the sunbirds simply sit on the ground to feed on the flowers – an observation that has been made with other low-growing sunbird-pollinated species.

Lachenalia in the Botanic Garden

Lachenalia aloides is in bloom at the
Botanic Garden right now if you want to
have a look at this interesting South African bulb.

The Botanic Garden has some specimens of Lachenalia aloides and other Lachenalia species in the glasshouses and, much like the plant Darwin is holding in the portrait, they are currently in bloom. The portrait would have been painted around this time of year, when there would have been very few plants in bloom. This further supports Nick’s conclusion regarding the species.

The Lachenalia story was one aspect of a lecture titled The Origin & Diversity of Flowering Plants, which was given recently by Nick Wray to the members of the annual Darwin Festival, held each February in Shrewsbury. The audience, made up of academics, ecologists, naturalists and keen amateur and professional gardeners, were taken through the flower pollination syndromes, illustrating the diversity that has evolved over millions of years. Nick discussed the work of the Angiosperm Phylogeny Group (APG) work, the planting of the APG III displays at the Botanic Garden and the difficult task of cultivating Amborella trichopoda and its place at the base of the extant living Angiosperm phylogenetic tree. The talk was illustrated by plants that were brought from the Botanic Garden. This created a lot of interest and added to the sense of place as the talk was held in the Shrewsbury Unitarian Church where Darwin’s mother took him and her other children to worship until Charles was thirteen. When, with an eye to his future university life, Darwin would have to attend a Church of England Church to ensure he would be eligible for a university course as students from Unitarian families would not be admitted.

The group were very appreciative of Nick’s talk and plan to make a summer visit to the Botanic Garden to enjoy the garden and explore its various evolution displays.

Notes:

1. Ellen Wallace Sharples met her husband in Bath where he was her tutor. After they married, the couple travelled back and forth a couple of times between England and America. When Ellen’s husband died in 1810, she moved to an apartment in Clifton with her two children (also artists) in 1811. She made her living doing portraits, as did her children. When she died in 1849, she left a substantial sum to the Bristol Academy which was instrumental in financing Bristol’s first art gallery, now the Royal West of England Academy.

Sources:

Campbell, S. 2009. ‘Sowed for Mr C.D’: The Darwin family’s garden diary for The Mount, Shrewsbury, 1838-65. Garden 
     History 37 (2): 1-16.
Campbell, S. 2012. ‘Its situation…was equisite in the extreme’: ornamental flowers, shrubs and trees in the Darwin 
     family’s garden at The Mount, Shrewsbury, 1838-65. Garden History 40 (2): 1-32.
Procheş, Ş., Cowling, R.M., Goldblatt, P., Manning, J.C., Snijman, D.A. 2006. An overview of the Cape geophytes. 
     Biological Journal of the Linnean Society 87: 27-43.
Turner, R.C., Midgley, J.J. 2016. Sunbird-pollination in the geoflorous species Hyobanch sanguinea (Orobanchaceae) 
     and Lachenalia luteola (Hyacinthaceae). South African Journal of Botany 102: 186-9.

Bumblebees who brave the winter

Posted on by andy.winfield

By Nicola Temple

This past weekend, my family and I met with friends in the village of Shipham, in Somerset, for a walk. It was torrential rain, yet we were determined. We dressed ourselves and three children under the age of 10 in waterproofs and set out. We arrived at a local country pub, not more than 3 km away, resembling drowned rats. And as a Canadian living here in the UK, I still marvel at the fact that nobody took one bit of notice at the state of us. It’s what you do. You get wet. You find a pub. You hunker down for a hot Sunday lunch. And you hope it tapers off before you have to head out again. (It didn’t.)

Pollinators, at least of the flying insect variety, aren’t terribly keen on this kind of weather either. Most hunker down for the winter months as there is generally not a lot of nectar to forage this time of year anyway. How they do this depends on the species. Honeybees reduce the colony to a minimal size and rely on their honey stores to see them through, while they dance in order to regulate the temperature of the hive. Most bumblebee colonies die out completely and the queens that mated at the end of the season find a place to hibernate. Solitary bees may hibernate as adults or as larvae, emerging only when the weather conditions are suitable. To each their own.

Martin Cooper spotted this buff-tailed bumblebee queen
foraging on his Mahonia flowers in Ipswich on a sunny
January day in 2015.
Photo credit: Martin Cooper [via Flickr CC]

However, there is one flying pollinator that can be spotted this time of year here in Bristol, and indeed, other warmer regions of the UK. It is the common buff-tailed bumblebee (Bombus terrestris). This species was first spotted during the winter of 1990, in Exeter. Sightings have been increasing ever since and include nest-founding queens, workers and males, suggesting this is a winter generation of the species.

The mated queen will emerge from her subterranean dormant state (diapause) during warm winter weather and set about establishing a new colony. The potential cost of waking up early is that the warm weather could be short-lived and temperatures could plummet. The benefit, of course, is that there’s nobody to compete with for food. If successful, the queen can establish a colony before the other pollinators even wake up from their winter nap.

Introduced plants provide winter forage

Of course, there is potentially another cost to emerging early – there could be nothing to eat. Bees are able to forage at temperatures around 0oC, but if there aren’t enough plants in flower, they won’t find the pollen and nectar needed to sustain the colony. Few native UK species flower in winter, but species introduced by avid gardeners to bring some winter colour to the garden, also bring some much-needed food to the buff-tailed bumblebee.

Researchers at Queen Mary University of London and The London Natural History Society, conducted a study of buff-tailed bumblebees foraging in London parks and gardens during winter about ten years ago. They wanted to see just how much food the bees were finding as food is directly related to the success of the colony.

The researchers found that there was plenty of forage to sustain the colonies and, in fact, the foraging rates they recorded near the end of winter were equivalent to peak foraging rates found in the height of summer. This doesn’t mean that the winter-flowering plants, such as the evergreen shrubs of the Mahonia spp., are providing more pollen and nectar than all the plants in the height of summer. But it does mean that each flower might have more pollen and nectar available because there aren’t other pollinators out and about also using the resource. The bumblebees, therefore, don’t need to go as far to find an equivalent amount of food and so they can collect it at a faster rate.  

Strategies for tolerating cold

Buff-tailed bumblebees aren’t as tolerant to cold as some other bee species; workers will freeze solid at about -7.1oC while queens freeze at -7.4oC. The bumblebees can obviously find warmth in the colony, but they need to forage and therefore be able to tolerate short spells of cold during the winter months. They may even need to tolerate cold temperatures for up to 24 hours as bumblebees often overnight away from the colony when they are unable to return from foraging.

Researchers from the University of Birmingham looked at the different cold tolerances of this bumblebee species a few years ago. They found that 50% of workers died after being exposed to 0oC for 7.2 days while queens could last over 25 days at this temperature – likely due to their fat reserves. However, as the forage study showed, the bees seem capable of finding food sources closer to the colony during winter months, which may reduce the likelihood of them having to endure cold temperatures for a lethal period of time.

These bumblebees may also have adopted some strategies to help reduce their possibilities of freezing. Pollen is an ice-nucleating agent in that it promotes the development of ice at higher temperatures. Other insects have been observed to expel any ice-nucleating agents from their gut when they experience low temperatures to avoid freezing. While this wasn’t observed in the bumblebees, it is a strategy that individuals might employ when caught out in the cold.

The more frequent observation of buff-tailed bumblebees in winter is thought to be a result of warmer autumn temperatures brought about by climate change. In a study from 1969, researchers reported a 6-9 month dormancy of all bumblebees in southern UK, so in a relatively short period of time there has been a considerable change in their seasonal pattern. There seems to be some flexibility in these patterns among bumblebees and for now, establishing winter colonies seems to be working for the buff-tails. However, with so many of our pollinators under threat, there is obviously also concern among the scientific community that more frequent extreme weather events could also spell disaster for these colonies that have selected to brave the winter months. As gardeners, we can perhaps do our bit by planting some winter forage species.

This year, the University of Bristol Botanic Garden will embrace a pollinator theme, with the aim of highlighting some of the lesser-known pollinators that are so important here in the UK. We love our pollinators, but research is still revealing so much about their unique and complex relationships with plants. So watch this space as we share some of these wonderful stories through our blog. We will also be posting pictures of pollinators we see in the Botanic Garden on our Twitter feed and Facebook page. But to see these pollinators in action, take some time to visit the Botanic Garden. Make space in your busy schedule to watch nature at its best – it’s worth it.

Sources:

Alford DV (1969) A study of the hibernation of bumblebees (Hymenoptera: Bombidae) in Southern England. Journal of 
     Animal Ecology 38: 149-170.
Owen EL, Bale JS, Hayward SAL (2013) Can winter-active bumblebees survive the cold? Assessing the cold tolerance of 
     Bombus terrestris audax and the effects of pollen feeding. PLoS ONE 8(11): e80061.          
     doi:10.1371/journal.pone.0080061
Stelzer RJ, Chitka L, Carlton M, Ings TC (2010) Winter active bumblebees (Bombus terrestris) achieve high foraging 
     rates in urban Britain. PLoS ONE 5(3): e9559. doi: 10.1371/journal.pone.0009559