What does June 21 mean to plants? Day length, temperature, sunlight, and water trigger all sorts of behavior in the world of plants…
Archives For pollination
History makes an appearance at the Orchid Show this winter
There’s something very special about this orchid. Can you tell what it is?
If you guessed that it was the long tubular structure coming from the back of the flower, you are right! That spur contains energy-packed nectar and is the reason this plant has a place in history.
Angraecum sesquipedale was first described in 1822 by French botanist Louis-Marie Aubert du Petit-Thouars and would be shrouded in mystery for decades after. It arrived in the United Kingdom 33 years later.
At the time this orchid was discovered, transporting plants from one continent to another was extremely difficult and often unreasonable. The long sea journey, combined with polluted conditions in industrialized cities, made it difficult to collect and maintain specimen plants. This would all soon change.
It was in 1829 that Nathaniel Bagshaw Ward discovered the mechanism that revolutionized horticulture and botany forever.
The Wardian Case
Nathaniel Bagshaw Ward was an English doctor who spent most of his life in eighteenth-century London. In his youth, he perused the writings of Linnaeus and spent some time in Jamaica, which fostered his love of entomology and botany. As an adult, Ward was inspired to create a wall of ferns and mosses in his own yard, but failed due to the polluted air of East London. He was distraught.
In the summer of 1829, Ward took a glass jar and placed a hawkmoth chrysalis inside, atop a bed of moist leaf mold. Ward regularly checked on the progress of the moth, finding that before it hatched, grasses and a fern emerged from the leaf mold. Ward observed that the glass jar retained moisture because as it warmed up, water evaporated, condensed on the glass, and returned to the base of the jar, never escaping. With this success he repeated his experiment and, to his delight, found that he could keep plants growing within the chamber for years. His discovery brought about the invention of the Wardian case, the predecessor to the modern terrarium. He wrote extensively about this in his book, On the Growth of Plants in Closely Glazed Cases. Soon the Wardian case became a popular feature of the parlor in Victorian society. These parlor versions, both tabletop and freestanding forms, often held one or more plants and could be rather ornate.
In 1843, the Wardian case was used for the first time to bring plants from China by sea. The director of the Royal Botanic Gardens, Kew, observed that in 15 years, the Wardian case brought six times as many plants as had been imported in the last century. If you do the math, that means it made importing plants almost 40 times as efficient as regular ocean travel! This was of particular use to collectors like James Bateman, a wealthy landowner who sponsored several plant exploration trips through the Royal Horticultural Society. One such trip would bring several rare Angraecum sesquipedale from Madagascar to England, and in 1862, this plant would find its way to one of the prominent figures in history.
By 1862, Charles Darwin had already become a prominent figure internationally. Having published On the Origin of Species three years earlier, Darwin was already the subject of scrutiny by religious groups and scientists who disagreed with his theories on evolution and natural selection. In this same year that he received a number of orchids from Bateman, Darwin published his book The Various Contrivances by Which Orchids are Fertilised by Insects, which proposed that Angraecum sesquipedale must be pollinated by a “huge moth with a wonderfully long proboscis” (or straw-like tongue). He proposed that it might be a Sphingidae moth since these are typically large. No such moth was known to exist on Madagascar.
Though largely overlooked by the public, his proposal became a subject of controversy, particularly in the religious community. Critics attributed any existence of such a creature to be by divine will and not natural selection; most mocked the possibility of such a moth existing. Others viewed his prediction with skepticism since only smaller moths had been discovered in Madagascar.
In 1903, 21 years following Darwin’s death, a subspecies of moth known as Xanthopan morgani praedicta, Morgan’s Sphinx moth, was found in Madagascar. This moth has a wingspan of 5 to 6 inches and a proboscis of 10 to 12 inches long. The subspecies name, praedicta, was intended as an homage to Darwin’s prediction that such an insect existed.
©2014 Chicago Botanic Garden and my.chicagobotanic.org
Summer romance is in the air on the shortgrass prairie of southeastern Colorado. Quite literally, the alluring fragrance of Harrington’s evening primrose (Oenothera harringtonii) wafts in the breeze when the plant blooms each evening. Insects from bees to moths follow the scent to the flower of their dreams.
The insect’s choice of flower is significant to the future of the plant species, according to Krissa Skogen, Ph.D., Chicago Botanic Garden conservation scientist. After a pollinator lands on a plant and sips its nectar, it may carry a copy of a plant’s genes, in the form of pollen, to the next plant it visits. That next plant may then take those genes to combine with its own to form a seed—creating the next generation of Harrington’s evening primroses.
How do pollinators select a flower? According to Dr. Skogen, floral scent heavily influences their choices in addition to floral color and size. “Floral scent is this fascinating black box of data that a lot of reproductive biologists haven’t yet collected,” she said.
After studying the many pollinators of the evening primrose, from bees to moths, she found that two species of moths called hawkmoths—or more specifically, the white-lined sphinx moth (Hyles lineata) and the five-spotted hawkmoth (Manduca quinquemaculata)—are most effective. She told me that 30 percent more seeds are produced when a hawkmoth pollinates a plant rather than a bee.
“What’s really awesome about this system is that these hawkmoths can fly up to 20 miles in a night, while bees typically forage within one to five miles,” she added.
An insect so large it is often confused for a hummingbird, the brown-and-white hawk moths can carry genes between the widely spaced evening primrose populations.
In fact, Skogen has genetic data that support this idea—the roughly 25 populations she and her colleagues have studied throughout southeastern Colorado really act as two to three genetically, because the hawkmoths do such a great job moving pollen over long distances.
Making Sense of Scent
How do the hawkmoths use floral scent to decide which flower to visit? According to Skogen, they detect scent at a distance in the air with their antennae as they fly. (Once they get closer, flower color and size become more important in locating individual flowers.)
Skogen and her colleagues have determined that flowers in some populations smell very different from each other, and these differences in fragrance can be detected by humans. Fragrance combinations include green apple, coconut, jasmine, and even Froot Loops™.
Skogen’s theories suggest that differences in floral scent may direct female white-lined sphinx moths to the best host plants for their eggs, attract enemies (including seed-eating moths), reflect differences in soil, or the floral fragrance of other plant species flowering nearby.
What combinations of genes create the scents that best attract the hawkmoths? What do the genetic data of existing plants tell us about the direction genes have moved in the past? Are other insects, such as herbivores and seed predators, helping to move pollen or inhibiting reproduction?
These are the questions Skogen and her research team, including the Garden’s Jeremie Fant, Ph.D., and students Wes Glisson and Matt Rhodes, will investigate further. Late this summer and in future fieldwork, they will monitor the pollinators and collect floral and plant-tissue samples.
Back in the Harris Family Foundation Plant Genetics Laboratory and the Reproductive Biology Laboratory at the Garden, they will compare the genetic data of these plants with the observed patterns of the pollinators, and other floral data.
Each trip is another step closer to having a positive impact on the future of the state-imperiled evening primrose and its choice pollinators. This species is endemic, growing only in southeastern Colorado and northern New Mexico where the unique soils best suit its needs.
Because the species grows in limited locations and is easily thwarted by the impacts of development, climate change, invasive weed species, and other intensifying threats, it’s especially important that its future generations are strong.
Skogen’s love for nature has been lifelong. As a child in Fargo, North Dakota, she enjoyed playing in unplowed prairies. Now, at the Garden, she visits Dixon Prairie as often as she can. “There is beauty in the natural distribution of species,” she said. “The prairie habitat is imprinted on me from those childhood experiences. It feels like home.”
©2013 Chicago Botanic Garden and my.chicagobotanic.org
Stranded, a purple coneflower stretches up from an unplowed slice of Minnesota grassland, signaling for help like a shipwrecked sailor on a desert island. Separated from its lifeline — a native prairie filled with plants and pollinators — it illustrates a widespread threat to the entire species.
This specimen arises with a few relatives from a remnant bound by railroad tracks and row crops. It is one of 27 study sites in Douglas County, Minnesota, evaluated each year by Stuart Wagenius, Ph.D., senior scientist at the Chicago Botanic Garden.
Although this plant may survive many more years, he says, it is unlikely to produce offspring due to its isolation. This is serious trouble for a species that relies on a habitat that has already dwindled to 1 percent of its original size.
Prairie, says Dr. Wagenius, “is one of the most endangered habitats in the world. We want to learn as much about it as we can in part because the opportunity is fading, but also because there are opportunities for us to conserve it.”
His research focuses on Echinacea angustifolia, or narrow-leaved purple coneflower, a prominent prairie species native to Minnesota. Begun as his doctoral research project in 1996, it has since become a lifelong mission. He wants to create an improved habitat for existing plants, and increase the species’ ability to reproduce and thrive.
Each year, he watches the plants on his study sites for damage from a triple-edged sword—pollination, genetic, and ecological issues.
The Pollination Puzzle
When the prairie stretched from horizon to horizon more than 100 years ago, Wagenius explains, a bee could have flown endlessly from flower to flower, carrying and delivering pollen. Are these insects still able to do their job?
Wagenius’s research has shown that the coneflowers continue to receive adequate visits from native bees. In fact, as he gave me a tour of his lab, he showed me an impressive collection of preserved sweat bees—small, emerald-green locals who have not succumbed to the plight of so many bees like the nonnative honey bees.
Instead, the problem is that the bees can only carry pollen so far. When they have few plants to work with in a small area, the pollen they deliver is not always accepted by the recipients.
The Genetic Glitch
After a few generations, Wagenius explains, all of the coneflowers in a small prairie become related, sharing pollen and some of the same genes. Then, if a bee delivers pollen with the same genes as the recipient plant, the pollen is likely to be rejected. In that case, no new seeds would be produced and no new generation of coneflowers would exist.
“Studying the genetics has offered some pretty good insight into what is going on in these small populations,” he says.
If related pollen is accepted, inbreeding can occur, which often results in weak offspring. Both issues diminish prospects for future generations.
Larger prairies are one potential solution to this problem. The other, Wagenius has found, lies right at his feet.
The Ecological Equation
In the past, natural fires on the land encouraged plants to flower, leading to new mating opportunities and refreshing local genetic diversity. Development meant the end of most of those fires. So, Wagenius and his team encourage trained land managers to restore fire through controlled burns.
When Wagenius returns to fieldwork this June, he plans to start with a blaze. He will conduct such a burn on a private landscape to increase the number of flowering plants and improve their chances of successful pollination and seed production.
A Family Affair
To begin fieldwork, he will meet on one of the larger study sites with his academic collaborators—including his wife Gretel, who is a botanist, and graduate and undergraduate students. His stay will be long enough that his other family members will join him there.
During fieldwork, he and his crew will measure the length and width of the leaves on each plant, and collect seeds that are later counted by Garden volunteers in a laboratory at the Daniel F. and Ada L. Rice Plant Conservation Science Center.
These characteristics help document the fitness of the plants. He will also compare the size of each preserve to the number of incompatible coneflower mates by studying the plants’ genetic patterns.
In addition, Wagenius will meet with local land managers and organizations to share advice on effective techniques. For example, he has suggested a controlled burn rather than plowing and replanting. “I’m glad to promote good conservation practices,” he says.
“I study habitat fragmentation and its consequences,” says Wagenius. Watch a video and learn more about his work.
Fortunately, many people would like to help him save the prairie, from duck hunters to farmers. “I’m in the role of not telling people to do more, but telling them how to do it better,” he explains. “I like being a person in our society helping others to do the right thing.”
This summer, a vision of hope rather than hopelessness will accompany Wagenius as he stands on the prairie with his research team and, well, a few relatives.
©2013 Chicago Botanic Garden and my.chicagobotanic.org