Sunday, February 7, 2016

Native species

Common milkweed, Asclepias syriaca (© B. Moisset)
Definitions of native plants abound. None is entirely satisfactory in all circumstances but each may serve a specific function. Some strive for scientific accuracy; others serve practical purposes. Moreover, in some instances the nativity of a plant may not matter to the native-plant gardener. None of us is about to give up growing tomatoes regardless of their non-native status.

The Federal Native Plant Conservation Committee proposes the following definition: “A native plant species is one that occurs naturally in a particular habitat, ecosystem, or region of the United States and its Territories or Possessions, without direct or indirect human actions.” Such definition may be useful for policy making.

The Lady Bird Johnson Wildflower Center of the University of Texas at Austin provides a sampling of definitions. Here are two:

“Native plants should be defined as those that have evolved and adapted to a specific location and have remained genetically unaltered by humans” (Wasowski. The American Gardener, 1998).

“All indigenous, terrestrial, and aquatic plant species that evolved naturally in an ecosystem” (US Forest Service).

Some may prefer other definitions from that list. In my opinion, the best ones are those that recognize the significance of co-evolution, habitats and ecosystems.

In North America, 1492 is commonly used as the cut-off date. It signals the arrival of Europeans on this continent and also the subsequent era of exploration of the entire planet. We may regard it as an arbitrary date; but it is one with practical usefulness as well as with historical significance. The numbers of introductions of non-native species and the distances to which they are transported started growing dramatically in 1492 and continue to grow at accelerated rates.

Humans have been introducing species to other lands from the beginning of agriculture (and unintentionally even earlier). Polynesians took pigs to Hawaii more than a thousand years ago. In recent times, Europeans introduced a new breed on the island. Is one breed more native than the other? Does it matter? We need to remember that the recently introduced breed is larger in size, more invasive, and more destructive of habitats. Habitat restoration may justify eradication of the European introduction. But removing the earlier breed, which is embedded in Hawaiian tradition and culture, would not be wise. This thorny issue will have to be decided by Hawaiians. I don’t envy them the task or the heated conflicts that this issue creates.

The Three Sisters of Native American agriculture –corn, squash and beans– are not truly native to North America. They were first cultivated in a region of Mexico and Central America several thousand years ago and carried farther north and east as well as into South America in prehistoric times. It is tempting to regard these crops as native plants, but they are not really so. Once again, the question is: Does it matter? Would those devoted to conservation and restoration want to eliminate these non-invasive, economically significant, long-established crops? Of course, not! This is not the purpose of restoration.

Further back, all species of organisms have been on the move at a certain point. To grow and multiply is a mandate as old as life itself. Those that successfully multiply need to expand their territories and invade new areas. The present geographic distribution of any given species tells us only a small part of the story. To understand the concept of native organisms, we need some knowledge of the origin, evolution, and dispersal of species and taxonomic groups.

We can use as an example that quintessential native plant, the common milkweed (Asclepias syriaca) and its relatives, the other milkweed members of the genus Asclepias.
Common milkweed flower and one of its visitors, a bumble bee (© B. Moisset)
The family of milkweeds originated in Africa many millions of years ago. Its members have been spreading out ever since. They occupied Asia, evolving into a number of new species along the way. They crossed the Bering Strait around 30 million years ago and, once again, they diversified into a number of related species. Nowadays, there are more than a hundred species of the genusAsclepias in North America. Some crossed the Isthmus of Panama and invaded South America, where they evolved into a handful of species. I find it very interesting that many millions of years later a mammalian species would originate in Africa and follow a similar itinerary all the way to the tip of Patagonia in South America. I am talking about us, Homo sapiens.
Geographic distribution of Asclepias syriacaUSDA map
USDA maps illustrating the geographic distribution of species ofAsclepiasSee the complete page
The USDA maps show the distribution of the common milkweed, Asclepias syriaca, and of other members of the genus. The common milkweed is found in all the Eastern United States and Canada and also in parts of the West. Other milkweeds occupy more limited territories, some overlapping each other. We can be certain that their geographic ranges have not remained constant in the thousands of years of their existences. They responded to climatic changes that caused glaciers to expand and retreat by migrating north or south and by contracting and expanding their territories accordingly. Still, we regard them as native to the areas where they are naturally present.

Adult monarch on common milkweed (© B. Moisset)

Milkweeds didn’t come alone. They are part of ecological communities that include other species, some tightly, other loosely, linked. Milkweed butterflies, having tied their destinies to those of milkweeds, followed their host plants. The genusDanaus originated in Africa and spread out along with milkweeds covering similar territories. These were the ancestors of the monarch butterfly (Danaus plexippus) and its relatives.
Longhorn milkweed beetles (© B. Moisset)
In fact, the southern monarch (Danaus erippus), a resident of southern South America, is so similar to the North American monarch that both were considered members of the same species until recently. Curiously, this southern monarch, like its northern sister, is migratory. Even more curiously, it migrates south to a colder climate, when winter comes. This is the kind of natural history mystery that keeps me awake at night. I hope that somebody uncovers the secrets of the southern monarch and lets me know.Monarch butterflies are not the only insects that take advantage of milkweeds. A whole menagerie has evolved to feed on these plants. There are milkweed longhorn beetles, large and small milkweed bugs, milkweed weevils, and milkweed tussock moths, just to name the most familiar ones. All of them are adapted to the strong milkweed toxins. These poisons remain in their tissues and give them some protection against predators, which find them inedible.

Lady beetle larva, Coleomegilla (© B. Moisset)
However, despite the protection that the milkweed toxins provide to its feeders, some predators and parasites are adapted to this inconvenience. Several species of birds and mice feed on monarchs, both in this country and in Mexico, where they spend the winter. A number of predatory and parasitic insects also depend on monarch butterflies for nourishment. Thus the milkweeds and their dependents and the other components of the food chain are all linked together. They have been co-evolving for millions of years and are functional parts of their ecosystems.

Silver-spotted skipper (© B. Moisset)
These relationships matter when we talk about native plants. A non-native organism, one newly arrived into an ecosystem, lacks this kind of co-evolved interactions with the other members of the community. It is not a functional component of the ecosystem. Eventually, new interactions will develop given enough time. This may take tens of thousands or millions of years. This is why the best definitions of native plants involve the words “co-evolution,” “habitat,” “community,” or “ecosystem.”

In some instances, it is hard to tell what is native. In certain cases, it may not be important or practical to consider the nativity of a plant, as in the example of the crops grown by Native Americans. That which really matters is the long established and complex relationships present in ecosystems. A native plant is one that is ecologically linked to other components of the ecosystem where it is found.

Some important concepts lack a perfect definition. We need to name them, nonetheless. Biologists would be lost if they couldn’t use the concept of “species” just because no definition fits all the circumstances. This word is not only important but absolutely necessary. One may need to use different definitions of “species” depending on the discipline; but that is no reason to give up the word. The concept of “native” organisms is equally necessary. It is here to stay, regardless of the difficulties that may arise at times.
Robins are among the birds that sometimes eat monarchs (© B. Moisset)
Originally published by Native Plants and Wildlife Gardens

© 2012, Beatriz Moisset. All rights reserved. This article is the property of Native Plants and Wildlife Gardens.

Friday, February 5, 2016

How much is a bat worth?

Big Eared Townsend Fleddermouse.PD-USGov, exact author unknown

Who would think of putting a dollar value on a bat? Well, it turns out that some researchers have done just that. I am not talking about a baseball bat but about that creature of the night so loathed by some. We tend to associate bats with witches and demons rather than with crops.

Is there a reason for putting an economic value on a bat? The answer is: Yes. Bats feed on flying insects at night. Many of those insects are pests that damage our valuable crops. So it turns out that bats are valuable to farmers.

A group of scientists have been trying to estimate the numbers of insects bats eat and the possible impact on agriculture and forestry if bats stopped supplying this pest control. They published their conclusions in the scientific journal, Science. Through a number of complex calculations of pesticide application and crop losses they came up with a range between $3.7 billion and $53 billion a year in the United States alone. It is not possible to be more precise when considering so many variables. Anyway the numbers are impressive.

It is worth mentioning that these maligned creatures have other functions in addition to the pest control discussed in this study. They are pollinators of many night blooming flowers. Cacti, in particular, are dependent on bats for pollination. Many cacti of the West synchronize their blooming time with the migration of some species of bats. Try to imagine what the West would be like without cacti.

Bat pollinating Agave desmettiana. © Carlos Machado

 Another service, especially in the tropics is seed dispersal. Bats eat the fruits of many trees, such as fig trees and pass the seeds far from the mother trees. It would be impossible to put a monetary value on this function, but it is becoming apparent that bats are essential to reforestation in tropical regions.

Unfortunately, in recent times, bats are encountering serious problems. There is one disease in particular that is decimating the populations of bats in the United States. This fungal disease, called "white nose syndrome", weakens and kills large number of bats, especially during the winter. It is for this reason that the researchers decided to investigate how the loss of bats would affect agriculture. Even lacking more accurate numbers the results are alarming; the losses to crops and forestry could be very serious.

It is only recently that a cure for white nose syndrome has been found. A bacteria attacks the fungus that causes this illness. Infecting bats with this bacteria cures them from the illness. Steps are taken to restore the health of bat populations. It is still a long road to complete success and reports of the illness spreading to other caves and to other regions continue. Cautious optimism is in order.

The web of life is intricate and often we don’t know enough about all the threads that make this tapestry. This is another example of a creature whose value we fail to recognize. It took a threat to the welfare of bats, such as the white nose syndrome for the world to stand up and take notice. We are only now beginning to appreciate the value of the free services provided by these creatures: pollination, seed dispersal and pest control. We have to look at bats with renewed respect. Let us develop a kinder attitude towards our friends, the bats.

Bat house © Robert Lawton

Bat conservation
White nose syndrome cure
Seed dispersal by bats

Sunday, June 28, 2015

What is native? What is not? When does it matter?

Common milkweed, Asclepias syriaca (© B. Moisset)
Definitions of native plants abound. None is entirely satisfactory in all circumstances but each may serve a specific function. Some strive for scientific accuracy; others serve practical purposes. Moreover, in some instances the nativity of a plant may not matter to the native-plant gardener. None of us is about to give up growing tomatoes regardless of their non-native status.

Some important concepts lack a perfect definition. We need to name them, nonetheless. Biologists would be lost if they couldn’t use the concept of “species” just because no definition fits all the circumstances. This word is not only important but absolutely necessary. One may need to use different definitions of “species” depending on the discipline; but that is no reason to give up the word. The concept of “native” organisms is equally necessary. It is here to stay, regardless of the difficulties that may arise at times.

Read the whole article in Native Plants and Wildlife Gardens.
or Archive Native Plants and wildlife Gardens
© 2012, Beatriz Moisset. All rights reserved. This article is the property of Native Plants and Wildlife Gardens.

Thursday, June 25, 2015

Thrifty flowers

Pollen is a valuable commodity. The less pollen needed, the more energy is left for other functions. Flowers resort to several strategies to economize on pollen. Some use a method called explosive pollination, others resort to buzz pollination. Both methods are well illustrated by official state flowers.

Mountain laurel in bloom. © Beatriz Moisset

Explosive Pollination of Mountain Laurels

Mountain laurel (Kalmia latifolia), Pennsylvania’s and Connecticut's state flower, has a singular way to ensure that its insect visitors carry pollen to other flowers of its species. The unopened blossoms present little knobs which give them a funny look. Their function becomes apparent when the flower opens. They are pockets that hold the anthers trapped. Anthers are the part of the flower that produces male cells, pollen.

Mountain laurel flower before an insect's visit.  © Beatriz Moisset
Flower tripped by an insect. © Beatriz Moisset
In most flowers the anthers are free and exposed to spread their pollen at the slightest touch of a flower visitor. The mountain laurel has a different strategy. The pollen is well protected against rain and wind; but, when a pollinator lands on the flower searching for nectar, the weight acts as a trigger, causing the taut stem of the anther to spring. The anther hits the pollinator gently on the back and gives it a dusting of pollen.

This method allows mountain laurel flowers to produce only a moderate amount of pollen because most of it ends up where it is intended, on the body of a pollinator, rather than being wasted in other ways.

Connecticut: Mountain laurel
Pennsylvania: Mountain laurel

Explosive Pollination of Pea-like Flowers

Texas Bluebonnet. Wikicommons © Jacopo Werther
Other flowers encase both the pollen-producing parts and the female parts, or stigma, into a sheath. Some members of the pea family, Fabaceae, have flowers that resemble a butterfly, this is why this subfamily is called Papilionoideae, papilio meaning butterfly. The top petal is large and shaped as the sail of a ship and is called the banner. Two side petals are called wings, and the bottom two petals are merged into one forming a sheath that encloses both the anthers and the stigma. This structure looks like the keel of a boat and it is so called.

Structure of a papilionoid flower. Wikicommons. © David Richfield
When a pollinator lands on a blossom, its weight triggers a mechanism causing the keel to spread open and the anthers and stigma jump up out of the enclosure. This is called tripping. The insect has to be heavy enough to cause such reaction. Some bumble bees are pros at this task; honey bees, on the other hand, dislike being pounced upon. After a few times, they learn to sneak around and steal the nectar through a small opening at the base of the keel. Only novices perform pollination. Once they learn this trick no more pollen is transferred to the stigmas. Nevertheless managed honey bees are widely used to pollinate alfalfa and clover. Bee hives provide a large labor force that makes up for this deficiency. Some bumble bees, especially the short-tongued species, are also inclined to a little larceny. However, they are generally considered highly competent pollinators of alfalfa and clover.

Clover, another papilionoid flower. © Beatriz Moisset
Texas’ bluebonnet (Lupinus) and Vermont’s red clover (Trifolium pratense) need to be tripped. Six species of lupines, all of them called bluebonnets because of their appearance, live in Texas. All six of them are considered the state flower. The red clover, Vermont’s state flower, on the other hand, is not a native plant. It is an important crop used to feed livestock.

Texas: Bluebonnet
Vermont: Red Clover

Buzz Pollination or the Salt Shaker Technique

Other flowers make the pollinators work for pollen in a different way. Interestingly enough, honey bees never learned how to do the job I will describe, but native bumble bees and numerous species of bees are real pros.

Azalea Andrena bee pollinating azalea. Observe the pores at the tips of the anthers. © Beatriz Moisset
In most flowers the pollen is made available to pollinators as soon as it is ripe. The anther splits open. We all have seen the golden dust many flowers have. If we touch it, it sticks to our fingers. Rhododendrons and azaleas do something else. They keep the pollen enclosed inside the anther. It can only come out through a small opening at the tip. Several other native flowers, like tomato and blueberry have a similar characteristic.

In order to extract it, the bee has to cling to the anther and give it a good shake. It accomplishes this by vibrating its flight muscles while keeping the wings still; it is like running the car engine in neutral. Pollen comes in clouds and clings to the body of the pollinator. Later, the bee proceeds to package its loot in the little baskets of the hind legs.

Buzz pollination of azalea. Video© Beatriz Moisset

Two states have official flowers that exemplify this method of pollination, Washington has chosen the Coast Rhododendron (Rhododendron macrophyllum) and West Virginia has another species of Rhododendron (Rhododendron maximum). Georgia’s official wildflower, azalea (Rhododendron prunifolium), follows the same system of pollination; its official flower is the rose; but, fortunately, they decided to honor a native plant in addition to a non-native flower.

Georgia (official wildflower): Azalea
Washington: Coast Rhododendron
West Virginia: Rhododendron

Other plants select their pollinator clientele through other methods. Some hide the nectar rather than the pollen. A different set of skills are needed to deal with these flowers as we'll see in the next post.


Thursday, June 18, 2015

Beginners Guide to Pollinators

The Amazon edition of Beginners Guide to Pollinators and Other Flower Visitors came out just in time for Pollinator Week, 2015.

Sample pages below:

Friday, May 22, 2015

This Way to the Restaurant.

Nectar guides © Beatriz Moisset

Nectar Guides

Most flowers want to make it easy for the visitor to find its way around. Thus, in addition to attracting pollinators with their colors and aromas, they guide their visitors in the right direction. This serves two purposes; it facilitates the task of the pollinator and enables the flower to have its pollen deposited where it is most needed.

Have you noticed the streaks of color radiating from the center of many blossoms? These are the nectar guides that tell the visitor: this is the way to the food. Violets and lupines are good examples. The variety of violets is amazing. We can count more than a hundred species and hybrids. Most of them are native, although a few have been introduced from Europe. As a footnote, it is worth mentioning that some violet species are the food plant of fritillary butterflies.

© Beatriz Moisset 

Don’t you find it rather surprising that the humble violet is the state flower of four states? It would be more correct to say violets, plural. Illinois did not attempt to specify which species, even after giving their flower the name of purple violet to distinguish it from yellow violets. New Jersey and Wisconsin chose the Viola sororia and Rhode Island, Viola palmata. Botanists and horticulturists pay attention to these things. However, legislators often ignore such details. This doesn't matter since all violets exemplify the nectar guides vividly.

Illinois: Purple Violet (Viola)
New Jersey: Common Blue Violet (Viola sororia)
Rhode Island: Violet (Viola palmata)
Wisconsin: Common Blue Violet (Viola sororia)

Texas bluebonnet © Jacopo Werther. Wikicommons

A slightly different type of nectar guides is present in bluebonnets (Lupinus). This Texas state flower includes all the species of bluebonnet that grow in that state. The guides become visible only when the flower opens and becomes receptive to pollinators. Bluebonnets belong to the pea family, Fabaceae, which is valuable to ecosystems because it enriches the soil by fixing nitrogen.

Texas: Texas Bluebonnet (Lupinus spp.)

Bull’s Eye

Some flowers use a different way to guide the pollinator to the desired place. It is called bull's eye. The color of the flower's center contrasts with the rest of the blossom. Several state flowers illustrate variations of this theme. Maryland's black-eyed Susan and Oklahoma's Indian blanket are fine examples. So are Florida's tickseed and Kansas' sunflower.

Sunflower © Beatriz Moisset 
Pollination researchers played a trick on visitors to these flowers to test the hypothesis that the bull's eye helped them find their way. They methodically pulled out all the petals of flowers of this type and glued them back in after reversing their position so that the darker part was in the outside. True enough, bees would land on the blossom, walk to the edge and stick their tongues out in search of nectar. They must have been mighty puzzled and annoyed at finding none.

Indian blanket. © Beatriz Moisset 

Some flowers, such as coreopsis, apparently lack this contrast. They appear uniformly yellow to our eyes. But bees see certain colors that escape us. They can see in the range of ultraviolet light, the so-called black light. The flowers, in turn, have a pattern that becomes visible only under this particular kind of light waves. The flower that appears uniformly yellow to us is seen by a bee as having a black center surrounded by a light halo.

Coreopsis. The bull's eye is visible only under ultraviolet light. © Beatriz Moisset 
Maryland, Florida and Kansas have state flowers with bull's eyes, black-eyed Susan, tickseed, and sunflower, respectively. Oklahoma is rather unusual in having not one but three types of flower symbols: the mistletoe as its floral emblem, the Oklahoma rose as its state flower and the Indian blanket, as its state wildflower. The latter has a conspicuous bull's eye.

Maryland: Black-eyed Susan (Rudbeckia hirta)
Florida (Wildflower): Tickseed (Coreopsis)
Kansas: Sunflower (Helianthus annuus)
Oklahoma (Wildflower): Indian Blanket (Gaillardia pulchella)

This article is about one of the many ways in which flowers increase the efficiency of the pollination process. In the next post we'll see examples of another strategy, frugality.


Black-eyedSusan under ultraviolet light
Dowden, Anne O. State Flowers. 1978
Cooper, Jason, The Rourke Guide to State Symbols. Flowers. 1942

Wednesday, March 18, 2015

Mass Appeal and Pollination

Some of the many visitors to goldenrod.  © Beatriz Moisset

Many flowers are not particularly selective; they welcome all kinds of visitors. They are wide open, easily accessible, thus many insects can reach the nectar and/or pollen regardless of whether their tongues are long or short. Such flowers provide a convenient standing platform to save their visitors the inconvenience of hovering over them. Their structure is simple so the pollinators don’t need to figure out how to open them in order to reach their rewards. Goldenrod is a fine example.
Monarch butterfly on goldenrod. © Beatriz Moisset
 I have spent countless happy hours observing goldenrods and photographing their numerous visitors. The one most common in my area is the Canada goldenrod. Several hundreds of species visit their flowers. Bear in mind that not all flower visitors qualify as pollinators. Some are not efficient at carrying pollen, or sit in one place for a long time and never make it to another plant. Such is the case of ambush bugs, whose only concern is to snare hapless pollinators to make a meal out of them. If you are interested on photographing and identifying pollinators this is a good place to start.

Metallic green bee. © Beatriz Moisset
 This plant blooms in the fall. It often gets blamed for allergies, but the real culprit is another plant that grows close by, sometimes intermingled with goldenrods, ragweed. Its flowers are inconspicuous because its pollen gets carried by the wind, not by officious pollinators. This is how it gets into our nostrils and causes our suffering. The much maligned goldenrods have larger, heavier and stickier grains of pollen that cannot get airborne and that require help from visitors.

Two states, Kentucky and Nebraska, have the goldenrod as their state flower. It is not clear which species of goldenrod Kentucky picked, but it is likely the Canada goldenrod (Solidago altissima). Nebraska’s choice is clearer, the giant goldenrod (Solidago gigantea). South Carolina, not satisfied with a state flower, also has a state wildflower. It is the Canada goldenrod. It is worth mentioning that Delaware has a state herb, the anise-scented or sweet goldenrod (Solidago odora).

Bumble bee on sunflower. © Beatriz Moisset

Coreopsis. © Beatriz Moisset
 Two other state flowers also have mass appeal. Like goldenrod, they are members of the daisy or aster family, easy to access by different kinds of visitors. They are Kansas’ sunflower (Helianthus annuus) and Maryland’s Black-eyed Susan (Rudbeckia hirta). It is worth mentioning here that two states, Florida and Mississippi, chose the tickseed (Coreopsis spp.) as a state wildflower in addition to their official state flowers, the orange blossom and the magnolia, respectively.

Kentucky: Goldenrod
Nebraska: Goldenrod
South Carolina (wildflower): Goldenrod
Delaware (herb): Goldenrod
Kansas: Sunflower
Maryland: Black-eyed Susan
Florida (wildflower): Coreopsis
Mississippi (wildflower): Coreopsis

The indiscriminate pollination strategy represented by all these flowers has advantages and also disadvantages. They suffer no shortage of pollinators. If one species is doing poorly one year, as it often happens in the insect world, there are plenty more to fill in the deficiency. However, sometimes too much of a good thing can be bad. Some of these non-specialized pollinators may be visiting a variety of flowers instead of being faithful to just one species so they end up carrying the wrong kind of pollen in such cases.

Blossoms with such mass appeal give me the opportunity to introduce the reader to the main groups of pollinators. They are all well represented on these mass appeal flowers.

Andrenidae bee © Beatriz Moisset
Bumble bee. © Beatriz Moisset
 Let us start by getting acquainted with bees. More than 80 species have been seen on goldenrods. Some of them deserve mention. Bumble bees are larger than other bees, plump, dark with yellow or white stripes, and hairy. Metallic green bees are small and gorgeously colored. They may escape notice if one isn’t very observant; but it is easy to become captivated by their shiny aspect. Mason bees and leaf-cutting bees carry pollen on their underbelly, unlike most other bees that carry it on their hind legs. Most of them are dark, nearly black and about the size of honey bees or slightly smaller.

Wasp. © Beatriz Moisset
 Wasps are related to bees and sometimes people confuse them. Most wasps are less hairy than bees and have narrow waists. They raise their young on a diet of insects or spiders, instead of pollen and nectar as bees do. Adult wasps need nectar to fuel their flight. Thus, they are frequent flower visitors and accomplish some pollination.

Syrphid fly. © Beatriz Moisset
Syrphid fly. © Beatriz Moisset

Many types of flies, including mosquitoes and gnats visit flowers to feed on their nectar. Some are good pollinators. The Syrphid flies, also called flower flies, are among the most assiduous flower visitors. Most of them mimic bees or wasps and are frequently mistaken for them. However, they don’t sting and there is no reason to fear them.

Buckeye butterfly on goldenrod. © Beatriz Moisset
Pyrausta moth on sunflower. © Beatriz Moisset
Yellow collared scape moth on goldenrod. © Beatriz Moisset
 Butterflies, skippers and moths have extremely long tongues that they can use like drinking straws when sipping nectar. They favor long necked flowers and carry pollen from one to another.

Polished lady beetle on sunflower. © Beatriz Moisset
Soldier beetle on goldenrod. © Beatriz Moisset
Finally, beetles, although not well specialized for pollination, are also capable of doing so in special circumstances. We already mentioned magnolia pollination by beetles. They also visit other flowers and can do a reasonably good job in some cases.

In the following chapters we’ll see flowers that have chosen a different strategy. They are pickier or more selective. Some attract a handful of visitors; a few go to the extreme of having relationships with only one species of pollinators.

Canada goldenrod visitors in IL.