- How is pollen propagated?
- What Is Pollen: How Does Pollination Work
- What is Pollen?
- Why Do Plants Produce Pollen?
- How Does Pollination Work?
- Pollen in the Garden and Allergies
- Why Flowering Plants Need Pollinators
- Everything You Need to Know About Tree and Spring Pollen Allergies 2020
- Pollen from a Plant’s Point of View
- Light and Dusty Pollen
- Heavy and Sticky Pollen
- Pollen from an Insects’ Point of View
- Pollen from a Gardener’s Point of View
- Pollen from an Allergy Sufferer’s Point of View
- Pollen from a Scientist’s Point of View
- How Pollen Works
- Pollen allergy
- What is pollination? And how does it work?
- Smallest and Largest Plant Pollinators
How is pollen propagated?
Pollen, or flower sperm, is a fine powder made up of microspores produced by male plants. Pollen carries the male reproductive cells (gametes) of seed plants, which include conifers (plants whose seeds grow inside cones) and flowering plants. Pollen starts out in the stamen, the male part of the seed plant, and needs to get to the pistil, the female part, in order for the plant to propagate.
There are two ways for a seed plant to be pollinated: self-pollination, in which the pollen from the stamen in one plant pollinates the pistil in that same plant, and cross-pollination, in which the pollen from the stamen in one plant pollinates the pistil in another plant of the same species.
But how does the pollen get from one plant to another? That depends on what kind of plant it is. The pollen of anemophilous (“wind-loving”) plants is very lightweight and easily dispersed by the wind. Many kinds of grasses and conifers are anemophilous. Researchers have found that the pollen of anemophilous plants can travel 2,000 feet (610 meters) up in the air and 25 miles (40.2 kilometers) away and still germinate 50 percent of the time.
In contrast, entomophilous (“insect-loving”) plants, including many flowers (though not all of them) are pollinated by insects. When insects land on an entomophilous plant to drink its nectar, some its heavy, sticky pollen sticks to the insects. The insects then move along from plant to plant to feed from them, and in the process the pollen from previous plants they landed on rubs off their bodies and onto the plants, pollinating them. The pollen from entomophilous plants doesn’t travel nearly as far as the pollen from anemophilous plants because an insect only travels a maximum of around 328 feet (100 meters) during its daily feeding.
What Is Pollen: How Does Pollination Work
As anyone with allergies knows, pollen is abundant in the spring. Plants seem to give off a thorough dusting of this powdery substance that causes so many people miserable symptoms. But what is pollen? And why do plants produce it? Here’s a little pollen information for you to satisfy your curiosity.
What is Pollen?
Pollen is a small grain made up of just a few cells and is produced by both flowering plants and cone-bearing plants, known as angiosperms and gymnosperms. If you are allergic, you feel the presence of pollen in the spring. If not, you likely notice it dusting surfaces, often giving things, like your car, a greenish tinge.
Pollen grains are unique to the plants they come from and can be identified under a microscope by shape, size, and the presence of surface textures.
Why Do Plants Produce Pollen?
In order to reproduce, plants need to be pollinated, and this is the reason that they produce pollen. Without pollination, plants will not produce seeds or fruit, and the next generation of plants. For us humans, pollination is so important because it is how food is produced. Without it, our plants wouldn’t make the produce that we eat.
How Does Pollination Work?
Pollination is the process of moving the pollen from the male components of a plant or flower to the female parts. This fertilizes the female reproductive cells so that a fruit or seeds will develop. Pollen is produced in flowers in the stamens and then must be transferred to the pistil, the female reproductive organ.
Pollination may occur within the same flower, which is called self-pollination. Cross-pollination, from one flower to another, is better and produces stronger plants, but it is more difficult. Plants have to rely on wind and animals to transfer pollen from one to another. Animals like bees and hummingbirds that make this transfer, are called pollinators.
Pollen in the Garden and Allergies
If you are a gardener and a pollen allergy sufferer, you really pay the price for your hobby in the spring. Pollen and pollination are essential, so you want to encourage it, yet you want to avoid allergy symptoms.
Stay inside on high-pollen days and days that are windy in the spring, and use a paper mask when in the garden. Put your hair up and under a hat, as pollen can get trapped in it and come in the house with you. It’s also important to change your clothes after gardening to stop pollen from coming inside.
Why Flowering Plants Need Pollinators
Pollination is a very important part of the angiosperm life cycle. It can happen two different ways.
Self-pollination is when pollen moves from one flower to another on the same plant, or even from an anther to a stigma on the same flower. Self-pollination has the advantage of occurring easily – plants need little or no outside help to move the pollen. But, any new plants produced are genetically identical to the parent plant. If something bad happens, like a drought, the identical plants have a reduced chance for survival.
Cross-pollination occurs when pollen, and thus genetic information, is transferred from one plant to another. It relies heavily on outside help from pollinators. Birds, bees, and butterflies are some of the best-known pollinators, but they’re not the only ones. Ants, beetles, moths, bats, and even non-living factors like water and wind can also do the job.
Relying on outside help is in some ways more risky compared to the sure thing of self-pollination. But, it’s estimated pollinators assist about 80 percent of flowering plants with reproduction. Sometimes, plants even block fertilization from their own pollen, and flowers often have special traits to attract specific pollinators.
What makes cross-pollination so important? It allows two parent plants to combine their genetic information. Their offspring may inherit desirable traits from both parents, or have fewer undesirable ones. If the offspring are hardier, or at least different from their parents, the chance of some plants in the group surviving an event like a drought and continuing to reproduce increases.
The relationship of angiosperms and pollinators is unique in the plant world, and it’s helped them become very successful. The genetic diversity supported by cross-pollination is why flowering plants live in almost all the Earth’s habitats, from deserts like Death Valley to ponds and oceans, and many places in between.
Most people look forward to the spring season. They finally get to come out from under their winter coats. The heat in their home is turned off in favor of sunshine and fresh breezes from windows that had been locked shut for months. New buds appear on the neighborhood trees. Flowers start to spring up out of the soil. The days start to get longer. And while most of these events are a reason for everyone to celebrate, any allergist will tell you that allergy sufferers describe the spring as the most miserable time of year.
During the spring months, pollen invades the air and cuts through your airways like cigarette smoke — you just can’t seem to get away from it no matter where you turn. While others are celebrating the new season, allergy sufferers are forced indoors.
So, what is pollen and why does it make allergy sufferers so miserable? Pollen is actually small spores that come from male trees and flowers. We often see the catkens (the remainder of the male part of the flowers and trees) that cover our cars, windows, and sidewalks making travel difficult for allergy sufferers.
There are generally two kinds of pollen:
- Sticky Pollen. This pollen is produced by plants and trees that have bright, ornamental flowers. This kind of pollen sticks to bees and is transported during flight, fertilizing other plants.
- Wind-Blown Pollen. This pollen comes from larger trees like pine and oak. The pollen is released in large quantities, fertilizing other trees of the same species.
If you believe you are suffering with allergies, you may find checking your local pollen count to be useful. The way the pollen counts are done is that pollen is collected on special rods. The pollen is then counted under a microscope. The pollen count is then calculated in grains per cubic meter of air.
People with allergies are known to experience sneezing, itchy, watery eyes, and may have some difficulty breathing. It is important to seek a diagnosis from an allergist in order to find a method that will ease your annual suffering. An allergist will ask questions about when and where your allergy symptoms tend to occur to make sure your allergy is not to other things like mold or even certain foods. Some allergists may prescribe yearly allergy shots while others may prescribe an over-the-counter antihistamine as the first line of defense.
You can’t get more natural than plants. Humans have been around them for our entire evolutionary history. So why are roughly 20 percent of Americans allergic to pollen, as if this plant sperm powder were some sort of toxic foreign substance?
The real question, according to Susan Waserman, professor of medicine in the division of clinical immunology and allergy at McMaster University in Canada, is not “Why pollen?” but “Why allergies at all?” Humans typically become allergic to things we’re frequently exposed to as children. Pollen is one of those things; in the spring, a cubic meter of air can contain thousands of pollen grains, so we’re inhaling them fairly constantly. But we’re also routinely exposed to food and pet hair as kids, and we commonly develop allergies to those, too.
So it’s not pollen, it’s just stuff. “If you’ve got that genetic tendency to become sensitized” — i.e. to develop allergic reactions to harmless substances — “the huge amount of pollen you breathe in and out can easily lead to sensitization,” Waserman told Life’s Little Mysteries.
If there’s nothing particularly heinous about pollen besides its prevalence, why do we develop allergies in the first place? The way it works is this: Allergies set in when your immune system misjudges a harmless protein, interpreting it as a threat. Once your system has gotten the wrong impression about a cat hair or pollen grain, there’s no changing its “mind” — you’re stuck with the allergy, often for the rest of your life.
The immune system will raise its defenses every time it detects the presence of the offending substance, or allergen. First, immune cells produce pitchforklike proteins called antibodies. Each antibody picks up an allergen molecule and carries it to white blood cells called mast cells, which trigger the release of chemicals like histamine. Those induce the allergic symptoms we all know and loathe: wheezing, sneezing, itching, swelling and rashes.
But why do immune systems make that fateful mistake in the first place?
There’s some evidence that allergies set in when you happen to be exposed to an allergen at the same time that you’re fighting off a virus, such as the common cold. “It’s entirely plausible that when the body is mounting a big immune response to a virus, that you’re going to trigger an allergic response to something you’re exposed to at the same time,” Waserman said. “But we don’t know definitely.”
Most studies of children getting “co-infected” by viruses and allergies have focused on pet hair allergies, she said, but the explanation may pertain to the onset of pollen and food allergies, too.
On the other hand, inadequate exposure to bacteria and viruses during early childhood also vastly increases the likelihood that you’ll develop allergies. Thanks to modern hygiene — antibacterial soap, clean water, pasteurized milk and more — kids aren’t exposed to nearly as many microbes as they used to be. As a result, their immune systems get fewer opportunities to learn how to discriminate between dangerous pathogens and harmless things like pollen. It’s called the “hygiene hypothesis,” but according to Waserman, it’s an accepted theory. “People whose immune systems are no longer busy fighting infection become disregulated and allergic,” she said.
Questions remain about why infectious disease exposure sometimes triggers but at other times stifles the onset of allergies, and what the perfect balance of filthiness and cleanliness might be during childhood. In the meantime, when the pollen count goes up on a lovely spring day, one-fifth of us are stuck indoors.
Follow Natalie Wolchover on Twitter @nattyover. Follow Life’s Little Mysteries on Twitter @llmysteries, then join us on Facebook.
Everything You Need to Know About Tree and Spring Pollen Allergies 2020
What do you do if you’re caught off guard without allergy medicine?
Here’s a great, quick remedy treatment you can use in case you find yourself in a situation where you can’t take medication or avoid your triggers.
First, check the pollen forecast. Then use nasal saline rinse or irrigation several times throughout the day during the worst of the tree pollen season. The saline irrigation removes pollen particles from the surface of your nasal passages, clears thick or crusted nasal drainage and soothes irritated nasal membranes.
There are a number of studies that found that patients with allergic rhinitis or chronic sinusitis who use regular saline rinses have less bacterial load and require fewer antibiotics. Using a rinse may also reduce your need for medication to control allergies.
You can buy saline rinse or irrigation kits at any drugstore and many grocery stores. These kits usually use a squeeze bottle or gravity to direct saline through the nasal passages. A common squeeze bottle technique is to position your head downward and rotated slightly to the left (do this over a sink). Gently squeeze some of the solution into your right nostril; the solution will come out through your left nostril. Now repeat on the other side.
Ready or not, tree pollen season is here! If you haven’t already prepared and expect you’ll need help this season, be sure to contact us today to schedule an appointment. This is a gorgeous time of year that should not be missed by staying indoors. Don’t suffer, we’re here to help.
Pollen from a Plant’s Point of View
Pollen has one purpose for the plant. It makes more plants. Sex is a real challenge for creatures that can’t move and meet one another, so plants have found a few good ways to move their genes from one flower to another, even when they are far apart.
Pollen is a white, yellow, or brown powder-like substance that is produced on the anthers of the flower, the male part of the plant. Pollen is used to fertilize the plant via the process of pollination, which is defined specifically as the transfer of pollen from the male anthers to the flower’s stigma, the female part of the plant. Pollination produces fruit and seed. Pollen contains the plant’s genetic code.
There are two types of pollen: light, dusty pollen and heavy, sticky pollen. These are useful because they allow pollination to happen in different ways.
Light and Dusty Pollen
Light and dusty pollen grains can be airborne and blown in the wind for long distances. Plants with tiny or inconspicuous flowers, such as grasses, corn, and many trees, generally have light, dusty pollen that blows on the wind. Some of the pollen lands on the stigma of a compatible flower, just by chance. The anthers have to make a lot of pollen, since most of it will never reach a female flower. If you ever visit a corn field while the plants are pollinating, you can actually see the pollen in the air, on the leaves, and on the ground. This is very expensive for the plants, but they do not have to produce colourful flowers or nectar to attract insects. Most of the pollen falls on the ground; only the tiniest fraction actually reaches another flower, and insects are neither attracted to the flowers, nor fed by their pollen.
Heavy and Sticky Pollen
Heavy and sticky pollen cannot blow in the wind and therefore pollination must be carried from flower to flower by insects. These plants provide nutritious pollen for the insects to eat, and in return the pollinators carry some of the pollen directly to other flowers. This is a far more economical arrangement compared to wind pollination, because the plant only needs to create a small amount of pollen. Such plants must make sure that one insect does not take too much pollen in one visit, without leaving anything for the next insect visitor. Many flowers force insects to come in contact with pollen while foraging for nectar by positioning the anthers in such a place that the insects will brush up against them. The pollen grains will stick the body of the insect, especially if it is hairy and electrostatically charged, as bees are. Some parts of the body cannot be easily groomed, keeping the pollen from being put in pollen baskets. This ensures the transfer of pollen when the insects visit other flowers.
Flowering plants requiring animal pollinators have to create big colourful flowers to attract insects, and they have to create sweet nectar to lure the insects inside. Their pollen is often also a more nutritious food source. All of this costs the plant a lot of energy, but it saves on the amount of pollen that it has to produce. Only a tiny amount of pollen is needed, since the insects act as an efficient delivery service.
Nearly three-quarters of all plants use this strategy, so it must be a winning partnership.
Pollen from an Insects’ Point of View
For pollinating insects, pollen is a perfect food. Rich in protein, it is one of the most nutritious substances in nature. Some bees collect pollen in special “baskets” on their bodies, to bring back to the hive for later use, or for winter food. If it were available in greater quantity, we would probably eat it ourselves, but the average flower produces only enough to feed a few tiny insects. Pollen is a vital food source to pollinators and also bee larvae. Pollen is very rich, containing 7-35% protein, as well as starch, vitamins, enzymes and pigments. Some plants do not produce nectar, and their pollen can be rich in lipids, including sterols, which are the building blocks of hormones and pheromones.
Pollinators are attracted to flowers with bright colours and strong scents. They are also attracted to nectar, a sugary liquid produced at the bottoms of flowers. This source of carbohydrates is like fast food for insects on the move. Nectar is their fuel during the foraging job. For most insects, pollen is secondary to nectar as a floral food reward.
Insects tend to get more pollen from older plant varieties. Many modern ornamental flowers are bred to have full, double-petaled shapes, which obstruct the pollen-bearing center parts. Some of these varieties are so difficult for bees and flies to access, that they cannot produce seeds without human hand pollination! Some modern varieties have less fragrance than the original varieties, or colours and shapes that are unattractive to insects. As well, there are some F1 hybrid flowers that have no pollen, such as pollen-less sunflowers, meant for cutting but not seeds. There is no need to avoid such flowers completely, but if you want to encourage native bees in your garden, be sure to plant some old-fashioned, single-flowered, richly-fragrant plants to provide food for your pollinators.
Pollen from a Gardener’s Point of View
Traditionally, the gardener’s view is that plants produce flowers, which either bear fruit or mysteriously fall off. This view must change to include the pollinator as a key part of the garden, and a full partner in the process of growing vegetables and fruit. Always a silent partner, it is the pollinator that has determined success for the cucumber grower, the melon or squash gardener, the berry or apple picker, and even the “lucky” gardener whose tomatoes are earlier, more prolific, and better shaped than their friends’. Even self-pollinating species benefit from the good vibrations of a bumblebee “buzz-pollinating” as it holds tightly to the flowers, shaking them and ensuring that they’re well pollinated.
Inside each female flower, each embryonic seed is fertilized by a different grain of pollen. A cucumber with 300 seeds needs 300 grains of pollen to fertilize it completely. Have you ever seen a cucumber or zucchini that looks like a half-inflated balloon? Insufficient pollination left part of it unfertilized, so the fruit didn’t bother to form completely. The same problem can be seen in misshapen strawberries or raspberries, and lumpy tomatoes or peppers. Some fruit, such as melons and squash, simply fall off prematurely if they aren’t fully pollinated.
Pollen from an Allergy Sufferer’s Point of View
Yes, pollen has its dark side. But fortunately for pollinators, it is only the wind-pollinated type of plant that causes allergies. Any pollen from a large-petaled flower is almost always heavy and sticky, to attach itself to a visiting bee that will carry it to another flower. Also, insect-pollinated flowers do not make much pollen. Wind pollinated flowers, such as grasses, maple, birch, and ragweed are to blame for allergies. They produce enormous quantities of lightweight pollen that carries easily with the wind, for miles. There is a common myth that plants such as goldenrod and sunflowers cause allergies, but this is false; those insect-pollinated flowers just bloom at the same time of year as the real culprit, ragweed.
Allergies caused by pollen are commonly referred to as hay fever. Hay fever is the most common allergic disease.1 One can only be allergic to the light and dusty pollen that is airborne, from wind-pollinated plants (trees, shrubs, weeds and grasses). The only way to have an allergic reaction to pollen from insect-pollinated plants is by direct contact.
Pollen normally enters the body via the nose and throat. The body’s immune system produces antibodies that fight against the antigens. Powerful inflammatory chemicals are produced, which act on tissues in various parts of the body, for example the respiratory system, causing allergy symptoms. Different kinds of pollen appear in the air during different times of the year, making pollen allergies seasonal. Some examples of trees that release pollen into the air are the maple, willow, birch, ash, oak, and pine. Examples of grasses and weeds include ragweed, russian thistle, sageweed, plantain, and nettle.
It is difficult to avoid airborne pollen. Pollen counts, given by local weather reports, is a measure of how much pollen is present in the air. It is a general guide for when it is better to stay indoors to avoid contact with pollen.
Pollen from a Scientist’s Point of View
As plants that rely on just wind, or even water currents, to move their pollen to the female reproductive flower parts grow, some of their pollen inevitably ends up in lakes, accumulating in the sediments. The structure of the pollen has characteristics that allow it to be identified, if not to species level, then to genus or family level (see Figure 1). Pollen is often well-preserved in sediments, due to its natural polymer called sporopollenin, one of the most inert organic substances known.2
The information in sediments includes the remains and traces of biota that lived in the lake and in the catchment area, and they are generally laid down in chronological order. These “records” of the past are very useful when we lack written historical data. We can access the information by taking sediment cores, which are sectioned and dated (using radiocarbon or other methods). Samples are prepared for microscopic analyses, and this allows researchers to identify and count the assemblages of pollen.
By understanding the present conditions that allow a tree or plant to grow (climatic conditions, soil constituents, geology, chemistry, etc.) we can correlate the pollen assemblages we find in core sections to reconstruct histories of climate, for example, or other variables of interest. For example, human disturbance is often noted by a sudden increase in ragweed pollen (Ambrosia species), because as European settlers arrived in North America, they cleared the land for development, and ragweed quickly dominates such landscapes.3
Pollen analyses, under the term palynology, are useful in many applications of ecology, archeology, even in forensic studies. Relatively recently, pollen analyses in Bosnia’s mass graves were used to convict war criminals involved in Srebrenica atrocities. If interested in this particular aspect, you can learn more here.
1. Do ragweed plants need insect pollinators?
2. Does goldenrod cause hayfever allergies?
3. Which can pollinate further, corn or pumpkins?
1. Ragweed has very light, dusty pollen that blows on the wind. You can tell because the flowers are small and not showy, so they aren’t meant to attract insects, and especially because the pollen causes allergies. People who suffer from hayfever are breathing ragweed pollen. In late summer, the small plants create so much wind-borne pollen that everyone winds up breathing it. Only a tiny amount ever lands on another ragweed flower to do its intended job.
2. Goldenrod is often blamed for allergies, but it has heavy, sticky pollen that never travels on the wind. Hayfever sufferers are really allergic to ragweed pollen, but the bright, showy goldenrod flowers are more obviously visible. It’s just a coincidence that they bloom at the same time of year.
3. Corn has light, dusty wind-blown pollen. Pumpkins have large, yellow, nectar-rich, insect-attracting flowers, and heavy pollen that can only be spread by insects. The question is: which travels further, the wind or the insects? The answer is that the native squash bee might only travel a maximum of about 100 meters during its daily feeding, but the wind can blow pollen up to three kilometers away.
How Pollen Works
Pollen grains take an endless array of fascinating shapes with all manner of textures and features. Dan Kitwood/Getty
Plants evolved pollen as a reproductive means more than 375 million years ago, and since then, they haven’t looked back . A large portion of the plant life that’s spread far and wide across the planet today displays this evolutionary ingenuity. The main reason pollen — and by extension the process of pollination — is so important, is because it means plants don’t have to rely on water to transport the biological components necessary for fertilization. Plants that bear pollen also tend to offer protection to their offspring after fertilization in the form of hard seeds — and in some cases, those seeds are even nestled inside fleshy fruits.
Pollen grains are, in essence, plant sperm. Or perhaps more technically, sperm sedans. Inside, they contain the male portion of DNA needed for plant reproduction. There’s great variation when it comes to the size of pollen grains, and there’s no correlation between the size of the plant and the size of the pollen it produces. Large plants might generate some of the tiniest grains of pollen, while diminutive plants may yield pollen that puts those to shame. Pollen grains may not look like much; to the naked eye, they often look like dusty specks, but upon closer inspection, they take an endless array of fascinating shapes with all manner of textures and features.
Whether conical, spherical, cylindrical or some other fantastical shape, many grains of pollen resemble something else, be it coral, succulent, seashell or sea anemone. Some grains are dotted with little spikes; others have weblike surfaces. Still more appear enshrined in ropey tangles, while others sport delicate dimples or have ribs that resemble the stripes on a watermelon.
Many of these unique adaptations are to help the pollen get where it needs to go — namely, its own species’ female counterpart. Surface features help grains cling to different modes of transportation, such as bird feathers, bee legs or animal fur. Or they help pollen sail through the air on appendages that resemble airplane wings or hot air balloons. Some of these features even help a pollen grain perform successfully when it reaches its destination. We’ll discuss what happens when that happy event occurs on the next page.
One of the chemicals released in this process is histamine, which is responsible for producing the symptoms of allergy, e.g. swelling, redness, itchiness and secretion of mucous. All of these symptoms can occur when the immune system recognises one or more of these pollen proteins and produces IgE antibody to it. Some proteins are more likely to become allergenic than others, and some pollen types carry proteins that are more allergenic. For example, pine is a prolific pollen producer, but very few people are allergic to the pollen proteins, whereas ragweed, which produces less pollen, has proteins that are very allergenic.
How can pollen be avoided?
We know that pollen concentrations vary in both space and time. Learn to identify the plants that you are allergic to (there are many books to help you), find out where they like to live and know at what time of year they are pollinating, then STAY AWAY. The highest concentrations of pollen are within 10 metres of the plant and concentrations drop quickly as you move farther away, so you can significantly reduce your exposure to pollen by removing yourself physically from the plant when it is pollinating. Also, keep your windows closed during this time and stay indoors, especially in the morning hours. Before and after the pollination period, the plant should pose no harm to you (unless you have a contact type of plant allergy), so you can take walks in the woods at these times. Pollination is one of nature’s wonders – learning about it helps us to cope with the bad luck of being allergic.
Based on information supplied by Christine Rogers
Department of Botany University of Toronto
What is pollination? And how does it work?
You’ve probably heard people talking about the importance of insect pollinators, and how we should protect them. But what exactly is pollination?
Basically, a flowering plant has to be fertilised with pollen before it can make seeds and produce another plant. If this didn’t happen, we’d soon run out of plants, and food!
What is pollination?
Flowers have both male and female parts. The stalks with pollen on the ends are called stamens and they are the male part of the flower. Right in the middle, there’s a female part called the stigma (this is quite hard to see). It’s the end of a tube which goes right down into the ovule, which is hidden inside the flower. This contains the ‘eggs’ which will grow into seeds. For this to happen, some pollen has to get into the ovule and fertilise the seeds.
Butterflies, wasps, moths and even flies pollinate plants. (Photo: Libby Owen/WTML)
How does pollination work?
Some plants can ‘self-pollinate’. This means the plant is fertilised when its own pollen finds its way from the stamens into the ovule. As they’re right next to each other, that’s not usually too tricky.
However, most plants are ‘cross-pollinated’. This means they need pollen from another plant of the same type to be fertilised. That’s where insect pollinators come in. Although it’s not just insects; some birds and bats are pollinators too. When a pollinator lands on a flower, some of the pollen rubs off on its body. Then, when it visits the next plant, it transfers some of the pollen so pollination can happen.
Some plants, such as grasses, are pollinated by the wind instead. Some people are allergic to pollen so when there’s a lot in the air, they get hay fever and are really sneezy.
What is pollen?
Take a close look at a flower. In the middle, you’ll see lots of stalks with yellow, powdery stuff on the ends. That’s pollen. It’s most often yellow, but it can come in other colours too.
Why do pollinators visit flowers?
The flowers produce nectar, a sugary liquid that pollinators love to drink. They also eat some of the pollen as it’s full of protein. The bright colours and scent of the flowers tells the pollinators there’s lots of yummy nectar and pollen inside!
Bees collect pollen and nectar for food. (Photo: WTML)
Did you know?
Most plants produce lovely smells to attract pollinators. But there are some that are very stinky. The dead horse arum lily produces a smell like (you’ve guessed it!) a dead horse so that it can attract lots of flies for pollination. Yuk! And then there’s the stinking root parasite flower that grows in South Africa. That one smells like poo!
In some plants, pollination takes place in the evening so that’s why plants like honeysuckle and jasmine smell gorgeous when it’s getting dark.
Find out more about woods and trees
Find out how to encourage pollinators in your garden, as well as which spring and summer flowers you can spot when you’re out and about in the woods.
Still looking for adventure? Why not become a family of Nature Detectives with a family membership? Kids get packs chock-full of seasonal fun and facts, all while supporting our native woods and trees!
“Are plants trying to kill us?” allergy sufferers often ask Deborah Devis.
A plant molecular geneticist at the University of Adelaide’s Waite campus in Australia, Devis should know the answer better than most. She is chugging through the last few months of a Ph.D. that involves predicting how grasses use pollen proteins that make people sneeze, wheeze and weep for days on end.
What’s known so far about what allergens do for pollens shed by grasses, trees and even mosses has nothing to do with revenge against a primate likely to attack them with mowers and other sharp tools, she says. Instead, plants are just trying to live like the rest of us.
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“In most cases,” she says, “the allergen proteins are absolutely essential.”
To understand why, a refresher on some basics of plant sex is helpful. A pollen grain’s stripped-down mission is to carry male sex cells to female parts of flowers. It’s a chancy and dangerous job. But evolution has honed formidable chemistry that protects the grains’ travels and fertilization itself. For instance, the outer coat of a pollen grain contains the outstandingly tough sporopollenin, which can last thousands of years, says Hannah Banks of Kew Gardens in London. Just to clean debris off the coat, researchers routinely boil pollen in a mixture of sulfuric and acetic acid.
When a healthy pollen grain finally lands on the female part of a flower, a tube from the grain starts racing down through the female tissue to fertilize the plant’s version of an egg, an ovule. Wind-carried pollen wafting off flowers in great clouds is particularly competitive, Devis says. Tobacco pollen, delivered by insect, sometimes waits a while before starting to grow and can take up to 12 hours to form a tube long enough to reach an ovule. In comparison, when Devis sprouted some normally wind-carried rice pollen on a microscope slide, the pollen tubes were too long to fit her view within just 15 minutes.
END GOAL Two pollen grains of the wild mustard Brassica kaber (colored and highly magnified in this scanning electron micrograph) demonstrate what pollen should do instead of wafting up a nose: Land on the female surface of a plant and race to grow a tube to fertilize an ovule. Dennis Kunkel Microscopy/Science Source
Profilins, a group of plant proteins containing allergens, matter in high-stakes plant sex, and in particular, the development of those tubes. (Profilins pop up at some stage in all life-forms with a cell nucleus, even a kind of amoeba with a profilin that can trigger reactions in allergy skin-prick tests in people and airway inflammation in mice, researchers from the University of Pusan in South Korea found in 2018.)
Plants need profilins for such fundamental jobs as assembling filaments into a cell’s basic framework. And in experiments at Cornell University in tomato plants (not wind-pollinated but easy to handle in the lab), suppressing a profilin gene sabotaged pollen tubes. “The pollen tubes can’t grow very long because there is no structure in place to keep on growing,” Devis says.
Similarity among different plants’ versions of profilin is “very, very high,” which shows how evolutionarily crucial the proteins are for plants, Devis says. The similarity suggests that “it’s just impossible, or very improbable, for any offspring that has a variation of those profilins to even survive.”
Another source of allergies are pollen proteins called expansins, which loosen cell walls, thus easing a pollen tube’s push toward the ovary. Sabotaging them turns pollen largely impotent. Without the normal expansins, “pollen tubes are just not making it to the ovule,” Devis says. Instead “they’re kind of clumping.”
Still other groups of pollen proteins that plants find useful can also trigger allergens in people. For instance, proteins active in plants’ stress responses or a cell’s use of calcium have proved allergenic, says aerobiologist Annika Saarto of the University of Turku in Finland.
Better understanding allergens’ jobs in pollen could help anyone who wanted to tackle the complex job of trying to engineer low-sneeze grasses, birch trees or other beloved but vexing plants, Devis says. But as alluring a dream as it may be for allergy sufferers, making allergen-free plants has its challenges. Because of the allergens’ vital roles for pollen, researchers can’t just engineer the structures all away. Scientists would need to use their knowledge of allergen functions to find some less- or non-allergy triggering substitutes.
And while tweaking one plant variety might be doable — say taming some oak or olive that helped push 10 of Europe’s urban parks into the ranks of high-allergy provocation — making a whole landscape of pollen-spewing plants less sneeze-provoking is daunting. “Not in my lifetime,” Devis predicts.
Smallest and Largest Plant Pollinators
By: H. Wayne Shew, Ph.D.
NAB Certified Pollen Counter
Angiosperms (flowering plants) and gymnosperms (mostly conifers) produce pollen. The pollen grain is the male gametophyte of plants and is analogous to sperm cells in animals; that is, it is needed for fertilization of the egg cell found in the female gametophyte of these plants. An obvious question is which plant species produce the most pollen? Do large plants produce more than small ones? Do trees produce more than weeds? The following are some generalities that can be made regarding pollen production by plants, but they are just that, generalities.
Trees do not necessarily produce the most pollen just because they are larger than herbaceous plants. Trees that produce large flowers, or even small flowers, but which form pollen that is large and “sticky” and which are insect pollinated will produce less pollen than trees that are wind pollinated or weeds and grasses that are wind pollinated. Trees like birch, elm, alder, ash, oak, mulberry, maple, and hickory are wind pollinated and produce large amounts of pollen that can cause significant problems for people each spring who are allergic to these tree pollens. Additionally, conifers such as cedar, juniper, cypress, and sequoia which are also wind pollinated, produce large amounts of pollen that trigger allergy symptoms in numerous individuals. These plants may start producing pollen in the winter and continue this production into the early spring. Therefore, the first generality that we can make is that wind pollinated plants will produce much more pollen than insect or animal pollinated plants.
Some plants produce perfect flowers (male and female structures in the same flower) while other plants are monoecious (male and female flowers are separate but on the same plant) or dioecious (plants are either male or female regarding the flowers they produce). A grove of male mulberry trees for example would produce a greater quantity of pollen than a mixed grove of male and female mulberry trees. It is not necessarily true that dioecious plants will always produce more pollen than monecious plants and if one considers the grasses you could even say that dioecious plants don’t always produce more pollen than plants having perfect flowers. However, the usual case is that plants with perfect flowers are less likely to be wind pollinated. Thus, a second generality that we can draw is that dioecious and monecious plants are more likely to produce greater amounts of pollen than plants having perfect flowers.
A third generality that we can make about pollen production is that plants that have the largest populations and which are widely distributed will produce greater amounts of pollen than species that are limited in distribution or who remain at low population levels. In general, plants we consider to be weeds are more widely distributed and reach higher population levels than plants we consider useful or aesthetically pleasing. Of course, the definition of a weed is any plant growing where you don’t want it; which could be roses or daffodils if they are in the middle of your vegetable garden. When we think of weeds that are significant pollen producers we typically think of plants such as plantain, ragweed, sagebrush, or lamb’s quarters. The other group of plants that are widespread and are present in large populations in some areas are the grasses, plant family Poaceae. Grasses have perfect flowers but are wind pollinated. They produce pollen grains that are difficult to distinguish from one another; all grass species form pollen grains which are monoporate and have an exine that looks very similar from one species to the next. Grasses such as Johnson grass, Bermuda grass, Kentucky blue grass, fescue, perennial rye grass, Paspalum species, etc. all produce large amounts of pollen that get into the air and become part of the aerospora.
Therefore, the best answer to our question regarding which plants produce the most pollen is, it varies. Method of pollination, types of flowers produced, and population size and distribution all affect the total amount of pollen produced by a given species. It would be safe to say that ragweed produces very large quantities of pollen. This is because ragweed plants are widely distributed, have large population sizes, are dioecious, produce small, nonsticky pollen grains, and are anemophilous.