Nature's Ancient Engineers

Young mushrooms of fly agaric, Amanita muscaria, in a northern Minnesota mixed coniferous-deciduous forest.The caps of the mushrooms will flatten and expand up to 10 inches wide.

Chances are, you recognize this mushroom. Fly agaric has long been known for its colorful cap, its hallucinogenic effects, and its supposed ability to attract and kill flies. It has also found its way into popular literature and media; It’s the Alice in Wonderland mushroom, the place where Smurfs live, and the Super Mushroom in Super Mario Bros. games. Unfortunately for some, it’s also poisonous, even deadly (1, 2).

Less known but much more significant is what fly agaric does below ground. The mushroom is just the visible part, the body that produces spores for reproduction. Underneath it is an extensive network of thread-like strands called hyphae (HY-fee), together called the mycelium (my-SEE-lee-um). The hyphae are like hunter-gatherers; they run through the soil and absorb water and nutrients to support the rest of the fungus.

Fly agaric also needs organic (carbon-containing) molecules, such as sugars and amino acids, the building blocks of proteins. Many fungi obtain these by breaking down dead organic matter in the soil. Fly agaric, though, goes about it differently: It barters with living plants.

The one above likely does business with white pine (Pinus strobus), red pine (Pinus resinosa), paper birch (Betula papyrifera) or quaking aspen (Populus tremuloides) in the northern Minnesota forest where it grew (3). Beneath the surface, its mycelium wraps around the tips of the trees’ roots, forming a sheath. Some of the hyphae in the sheath grow into the root and form a net around some of the cells. That’s where the exchange occurs: The fungus gives water and nutrients to the plant, while the plant gives organic molecules to the fungus. 

Illustration of an ectomycorrhiza, which forms a sheath around root tips. Hyphae cross the epidermis and enter the root cortex. There they form a net, called a Hartig net, between the cells. The unit of measurement in the upper right scale is 100 microns. One hundred microns is the approximate width of a human hair. The photographs are colorized images produced by a scanning electron microscope, or SEM. Illustration by Atrebe10, licensed under Creative Commons Attribution-Share Alike 3.0 Unported license, via Wikimedia.

This symbiotic relationship is called a mycorrhiza (MY-co-RY-za), literally “fungus root.” The sheathing type, called an ectomycorrhiza, is relatively new, about 200 million years old give or take a few million years. An older type, roughly 400 million years old, doesn’t sheath a plant’s roots but instead grows inside the root cells themselves, where the exchange of nutrients, water and organic compounds occurs. This type is called an endomycorrhiza or arbuscular mycorrhiza, the latter named for the tree-like growth, called an arbuscule, the fungus forms inside the cells.

Development of mycorrhizae (plural, ending in -zee) was critical to the transition of plants from water to land hundreds of millions of years ago (4, 5 7). These early land plants had no roots or vascular (conducting) tissues. Those that eventually developed symbiotic associations with fungi had an advantage, because mycorrhizae could extend the plant's reach into the soil to obtain water and nutrients. Mycorrhizae were so beneficial that they developed independently many times over, involving different plants and fungi (6).

Given that far-reaching history, it’s no surprise that there are more types of mycorrhizae than the two described above. Ecto- and endomycorrhizae are the most common, but there are at least two more types (6). Whatever the type, in most cases both partners benefit and often are dependent on each other for survival. Without their association, neither partner would thrive. Their ecosystems wouldn’t, either.

That’s because approximately 80% of modern terrestrial plants are mycorrhizal, although the percentage of such plants in a community can vary (7). Prairies, deciduous forests, coniferous forests, and other terrestrial ecosystems are generally dominated by mycorrhizal plants. They are the foundation of these systems, supporting all the trophic (feeding) levels above them. A mycorrhizal white pine, for example, grows the cones that hold the seeds that feed a variety of birds and mammals, which in turn have their own roles in their communities.

Mycorrhizae are so important to ecosystems that restoring highly disturbed places, such as mines and abandoned agricultural fields, can be helped by adding mycorrhizal fungi to soils or seeds when restoration begins. Mycorrhizae have also been suggested as possible remedies for high carbon dioxide levels in our atmosphere, because they can help move carbon below ground. These practices will be the subjects of the next post.

References

1.      Two cases of severe Amanita muscaria poisoning including a fatality. Ethan M. Meisel, MD, and others. Wilderness and Environmental Medicine, Vol. 33, No. 4, 2022.

2.     Notes from the field: Acute intoxications from consumption of Amanita muscaria mushrooms — Minnesota, 2018. Joanne Taylor and others. MMWR Morb Mortal Wkly Rep 2019, Vol. 68: pp. 483–484, 2019.

3.     Fungus associates of ectotrophic mycorrhizae. James M. Trappe. Botanical Review, Vol. 28, No. 4: pp. 538-606, 1962. Available for reading with a free JSTOR account at https://www.jstor.org/stable/4353659.

4.     The origin and evolution of mycorrhizal symbioses: from palaeomycology to phylogenomics. Christine Strullu-Derrien and others. New Phytologist, Vol. 220, No. 4: pp.1012-1030, 2018.

5.      History of mycorrhizae. Jake Sun, Lindenwood University. The Confluence, Vol. 1, No. 2: Art. 2, 2022.

6.      Mycorrhizal Fungi. Society for the Protection of Underground Networks. Website accessed February 3, 2025.

7.      Coevolution of roots and mycorrhizas of land plants. Mark C. Brundrett. New Phytologist, Vol. 154, No. 2: pp. 275-304, 2002. 

Are Fungi Plants?

In early classification systems, these morel mushrooms (Morchella esculenta) were included with plants.

 
At one time, morel mushrooms and other fungi were considered plants. That was when all life was classified as either plant or animal, and morels sure didn’t look like animals. They emerge from the soil, they don't move, and they produce “fruiting” bodies (mushrooms) for reproduction. In addition, its cells are surrounded by rigid walls, as are the cells of ferns, grasses, trees and other living things that are true plants. (Most bacterial cells also have walls, but that's another topic.)

It wasn’t until the 1960s that fungi were placed in their own kingdom. Ecologist Robert Whittaker thought they should be separated from plants because they are decomposers, not producers. In other words, they break down and absorb organic matter, whereas plants make organic matter by photosynthesis. In ecologists’ terms, fungi are saprotrophic (literally, rot feeders) whereas plants are autotrophic (self-feeders). There are exceptions in each group, but they’re in the minority.

Other differences became apparent as the decades went by. Fungal cell walls, for example, are made of chitin, long chains of modified glucose molecules. That’s the same material that forms the exoskeletons of insects. Plant cells, however, are mostly cellulose, twisted and bundled chains of glucose without the modifications present in chitin.

Other differences appear inside their cells. Fungal cells have no chloroplasts, the organelles where photosynthesis takes place. They also lack chlorophyll, the green pigment primarily responsible for absorbing light energy. That makes sense, since fungi aren’t photosynthetic.

Plant cells (left, from a moss) contain chloroplasts, the green organelles where photosynthesis takes place. Fungal cells (right, from a Morchella, or morel, mushroom) do not. This is one difference between plants and fungi. Moss cells: Kelvinsong, CC BY 3.0, via Wikimedia Commons. Morchella cells cropped from image by Marc Perkins CC BY-NC 2.0, via Flickr.

There are other differences, but maybe these are enough to show that fungi and plants aren’t closely related. Even so, the line between them can be muddy. Some older botany textbooks include at least a chapter about fungi. And as mentioned above, mushrooms and other large reproductive bodies are still called “fruiting” bodies, even though they’re not at all like the fruits produced by flowering plants.

It can be confusing. What’s not confusing or unclear is that fungi, though not plants, are important to plants for many reasons. For example, fungi made it possible for plants to colonize land, a step in development not only for plants but for entire terrestrial ecosystems. More on that in the next post.

The Color of Survival

These blackberry leaves (Rubus species) displayed multiple colors this fall.

If conditions are favorable, fall gives us a brilliant display of yellow, orange, red and almost purple leaves. As green fades and other colors appear, leaves are also revealing what makes them tick. The pigments in their blades aren’t just for show. They’re workhorses, and their tasks are critical to a plant’s survival. 

The following sequence shows a leaf of highbush cranberry photographed from September into November. As the season progresses, the blade changes from green to orange-red to dark red, each phase produced by a different set of pigments, each set with a different purpose. The leaf was photographed in 2008.

September 20

The leaf is green from the pigment chlorophyll. Two nearly identical forms of chlorophyll, called chlorophyll a and chlorophyll b, absorb mostly red and blue light and reflect green. These pigments are vital for photosynthesis, the process that converts light energy into chemical energy in the form of glucose. 

October 11

As day length shortens and temperatures fall, chlorophyll production slows. As green fades, yellows, oranges and scarlet reds appear. These colors are from carotenoids, pigments that have been there all along but have been masked by chlorophyll. Carotenoids are accessory pigments in photosynthesis; they absorb blue and green light, expanding the wavelengths available to power this process.

 

October 19

As chlorophyll continues to be degraded, more carotenoids are visible. The leaf blade is distinctly pale green with larger areas of light red. This trend continues as the days pass.

 

October 27

Nearly all chlorophyll is gone and more carotenoids are revealed. At the same time, darker red pigments called anthocyanins begin to form. These pigments need sugars to develop, so their deep red to purple hues are muted when fall months are cloudy and rainy and photosynthesis is limited. Some plant species produce only small amounts of anthocyanins. Highbush cranberry, dogwoods, red oak, red maple and sumac are among those that produce higher amounts.

November 1

Abundant anthocyanins now mask the carotenoids. Anthocyanins absorb yellow, green and ultraviolet light but are not involved in photosynthesis. At one time they were considered a useless waste of a plant's energy. Now, though, they're thought to block excess light energy from damaging leaf tissues, similar to sunscreen. Anthocyanins can also form in other stressful conditions, such as drought, high salinity, and nutrient deficiency.

Chlorophyll, carotenoids and anthocyanins may be present in other parts of plants, too. Flowers, fruits, stems and roots -- carrots, for example -- bear many kinds of pigments, and their roles in those organs may be different from those in leaves. The color of survival is complex. 

Learn more about leaf pigments and photosynthesis:

Absorption of light. LibreTexts Biology. 

Leaf Pigments. Harvard Forest.

When and why leaves change color. Minnesota DNR.

Plant Profile: Zigzag Goldenrod

 Solidago flexicaulis | Family Asteraceae (Aster) 

Zigzag goldenrod along a woodland edge in August.

Zigzag goldenrod, also called big leaf goldenrod, is a native perennial of forest edges and openings. It’s literally a late bloomer, flowering from August into October with narrow, upright clusters of yellow-gold flowers at the top of the plant and from the upper nodes.

Each “flower” is actually a group of small flowers in a head inflorescence, an arrangement typical of plants in the aster family. The central flowers, called disk flowers, have small, recurved, yellow petals that are easiest to see with a magnifying lens. Around them are several ray flowers, so called because each bears a single, petal-like ray. Zigzag goldenrod heads typically have 3-5 rays at their peak.

Left: A single head of small flowers. Two rays are visible. The "spears" emerging from the flowers are stamens and pistils, the reproductive parts of the flower. Right: A single head dissected to show disk and ray flowers. The white threads at the base of the flowers are a group of modified sepals called a pappus.

At the base of either kind of flower are white, thread-like, modified sepals, together called the pappus. Unlike the leafy or petal-like sepals many plants have, these tiny filaments persist after flowering. They are attached to the top of small, linear fruits called achenes (ah-KEENS). A single plant produces hundreds (thousands?) of them, each carried by wind with the help of its parachute-like pappus.

Left: The fruits on this zigzag goldenrod are ready to catch the wind.
Right: Individual achenes, each just a millimeter or two long and topped with a spreading pappus. 

Even before it flowers, zigzag goldenrod is easy to recognize. As its name suggests, the stems typically zig and zag from one node to the next. The pattern is subtle, but it’s still a good identifying characteristic.

The name “big leaf” refers to the lower leaves, which are egg-shaped and up to 4 inches wide and 6 inches long. Their margins (edges) are coarsely toothed and their petioles are winged, especially where they meet the leaf blades. Farther up the stem, the leaves are smaller and lance shaped.

Left: A stem with a typical zig zag pattern. Upper right: Lower and middle leaves are egg shaped and sharply toothed.
Lower right: Upper stem leaves are lance shaped, becoming smaller up the stem.

Zigzag goldenrod spreads not just with seeds but also with rhizomes to form colonies. It isn’t as aggressive as Canada goldenrod, but patches will expand noticeably in a few years. That’s helpful where cover is desired but not so helpful in formal gardens, where plants are often preferred to stay in place.

Zigzag goldenrod is pollinated by a variety of insects, including bees, flies, wasps and butterflies. Goldenrods in general, along with asters, are important sources of food for pollinators late in the season. Goldenrods also host insect larvae, such as the colorful caterpillar of the brown-headed owlet moth.

Left: A bumble bee pollinates zigzag goldenrod while gathering nectar and pollen.
Right: A caterpillar of the brown hooded owlet moth feeds on zigzag goldenrod.

It’s hard to fault zigzag goldenrod for anything, but goldenrods in general have a reputation for causing seasonal allergies. Their pollen, however, is relatively heavy and sticky, ideal for attaching to insect bodies but not for catching the wind. The pollen of common ragweed and giant ragweed, however, is light, dry and wind-borne, and it’s released from mid-summer to mid-fall, about the same time as goldenrods. Also, ragweed grows in the same dry, sunny habitats that favor some goldenrods, so the latter gets a bad rap.

It’s undeserved. No need for tissues to enjoy zigzag goldenrod. Just a semi-shady spot and an appreciation for this golden yellow pollinator magnet.

References

Minnesota Wildflowers

Board of Water and Soil Resources

Blue Thumb

Illinois Wildflowers

Plant Profile: Wild Carrot

 Daucus carota L./Carrot family, Apiaceae

Wild carrot, Daucus carota, growing along a roadside near Maple Plain, MN, on August 10, 2024.

Wild carrot, also called Queen Anne’s lace, is a Eurasian biennial introduced to North America by colonists for food or medicinal use. It produces basal rosettes of carrot-like leaves the first year and leafy stems topped with umbels (umbrella-shaped clusters) of small, white flowers the second year. It blooms in mid- to late summer, typically in the dry soils and full sun of disturbed sites, such as abandoned lots, old fields, rail corridors, and roadsides. It spreads by seeds, and they are abundant. Because a single plant blooms continuously in its second year, that plant can produce thousands of seeds before it dies.

As the name “wild carrot” suggests, this is the ancestor of cultivated carrots. Wild carrot’s taproots are carrot-like in shape and smell, although they’re narrower than cultivated carrots and become bitter and woody with age, especially in the plant’s second year of growth.

Although some sources caution against eating wild carrot, it’s generally considered non-toxic and edible. Large quantities can raise blood pressure or make it difficult to regulate (1). In some people, sap from the plant can irritate the skin when it’s exposed to sunlight, a condition called phytophotodermatitis, literally “plant-light-skin inflammation” (2, 3, 4). In addition, carrot greens, presumably from cultivated carrots, are listed as mildly toxic on the list of poisonous plants from the MN Poison Control System, now the Minnesota Regional Poison Center. Wild carrot greens may have the same effect.

Deadly Look-Alikes

The much greater danger in foraging wild carrot is mistaking deadly look-alikes for this plant. Water hemlock (Cicuta maculata) and poison hemlock (Conium maculatum), also in the carrot family, resemble wild carrot and have accidentally been added to salads or sampled in the field or garden. The result can be severe illness and even death caused by the plants’ alkaloids, compounds many plants produce to deter herbivores. All parts of these plants are toxic.

Three look-alikes. From left: Wild carrot, water hemlock, poison hemlock. Water hemlock photo by Rob Routledge, Sault College, Bugwood.org. Poison hemlock photo by Eric Coombs, Oregon Department of Agriculture, Bugwood.org.

Accurate Identification is Crucial

Several resources help identify wild carrot and its look-alikes. A plant identification sheet from the University of Minnesota Extension Service contrasts poison hemlock with ten other plants, including water hemlock and wild carrot. An article by the Clearwater Conservancy in Pennsylvania includes a table contrasting the characteristics of seven members of the carrot family, including those featured here. The Minnesota Department of Transportation also has a guide to identifying poison hemlock and its look-alikes..

Here are some additional tips.

Tip 1: Wild carrot umbels sometimes have a dark red or purple flower in the center. Beneath the umbels are long, branched bracts. After flowering, the umbels curl up and in to form a bowl or nest. That’s why wild carrot is sometimes called bird’s nest. Neither water hemlock nor poison hemlock have these characteristics.

 

Left: After flowering, wild carrot umbels turn up and in to form a small nest. Notice the long, branched bracts below the umbel. Right: A purple flower in the center of a wild carrot umbel (arrow). Not all umbels have them.

Tip 2: The plants are hardest to distinguish in their first year of growth, when they produce only basal leaves. All three have pinnately divided leaves, but wild carrot leaves are narrower in outline and more finely divided into narrower leaflets. The leaves of both water hemlock and poison hemlock are broader, triangular in outline, and have wider leaflets. Poison hemlock leaves are often described as fern-like.

 

From left: Leaves of wild carrot, water hemlock, and poison hemlock. Not to scale. Water hemlock photo by Steve Dewey, Utah State University, Bugwood.org. Poison hemlock photo by John Cardina, The Ohio State University, Bugwood.org

Tip 3: Habitat and flowering phenology differ somewhat among these plants, but because they overlap, they are less reliable characteristics. In general, wild carrot thrives in sunny, well-drained, disturbed places such as pastures, old fields, roadsides, and railway corridors. In Minnesota it flowers as early as May and as late as October, but more typically from July to September.

In contrast, water hemlock is an obligate wetland plant. It needs the moist soils of wet prairies, wet meadows, marshes, and streambanks. It flowers from June to September. Poison hemlock also prefers wet or moist soils, but it will tolerate drier conditions. Its habitats include streambanks, ditches, roadsides, and pastures. It flowers in June and July.

If You Find Poison Hemlock

Because poison hemlock, an introduced plant, is so hazardous and because it’s not yet so widespread in Minnesota that it can’t be controlled, its locations should be reported to Report A Pest or EDDMapS. Do not remove it without taking serious precautions. Better yet, hire a professional (5).

Cited References

1)     Wild Carrot. Missouri Poison Center. Accessed August 11, 2024.

2)     Wild Carrot. Minnesota Department of Agriculture. Accessed August 11, 2024.

3)     Phytophotodermatitis Clinical Presentation. William P. Baugh, MD. Editor William D. James, MD. Medscape. Updated November 4, 2021.

4)     Queen Anne’s lace (Daucus carota). Minnesota Department of Natural Resources. Accessed August 12, 2024.

5)     Poison hemlock. A. Gupta, A. Rager, and M. M. Weber. University of Minnesota Extension Service. Reviewed in 2020. Accessed August 12, 2024.

Additional References

Daucus carota (Queen Anne’s Lace). Minnesota Wildflowers. Accessed August 12, 2024.

Water Hemlock. G.D. Bebeau, The Friends of the Wildflower Garden, Inc. Accessed August 12, 2024.

Cicuta maculata (Water Hemlock). Minnesota Wildflowers. Accessed August 12, 2024.

Poison hemlock (Conium maculatum). Minnesota Department of Natural Resources. Accessed August 12, 2024.

Poison Hemlock. Minnesota Department of Agriculture. Accessed August 12, 2024.

Poison hemlock (Conium maculatum). Minnesota Department of Natural Resources. Accessed August 12, 2024.

Minnesota Noxious Weed List. Minnesota Department of Agriculture. Accessed August 12, 2024.

Chadde, S.W. 2012. Wetland Plants of Minnesota. 2^nd ed. A Bogman Guide.

Plants for Bee Specialists

Jerusalem artichoke, Helianthus tuberosus, is one of several sunflower species favored by the sunflower mining bee, a specialist pollinator.

The sunflower mining bee, Andrena helianthi, has discriminating tastes.

This native bee is a specialist, gathering pollen primarily from plants in the aster family, Asteraceae (formerly Compositae, also called composites). To be more specific, it favors pollen from plants in the genus Helianthus, the sunflowers, to feed its larvae. (1).

In pollinator terminology, the sunflower mining bee is oligolectic, meaning “few chosen.” It’s far from alone in having narrow food preferences. According to the recent Minnesota Statewide Bee Survey (2), about 30% of the nearly 360 bee species confirmed in the survey are oligolectic.

Benefits and Drawbacks of Oligolecty

Given that high number, there must be advantages to oligolecty. One possibility is that the bees co-evolved with a few host plants that offer more digestible pollen (3). Entomologists at the University of Wisconsin found that the larvae of the blueberry mason bee, Osmia ribifloris, thrived when fed preferred host pollen that also included the microbes naturally found in that pollen. In contrast, larvae fed microbe-free pollen from the preferred host plant were much less fit, and larvae fed pollen from non-host plants had intermediate fitness (4).

Plants benefit from the relationship, too. Species visited by oligolectic bees have dedicated pollinators that transfer pollen among only a few kinds of plants, which makes successful pollination more likely. The plant loses less pollen to insects that carry it to a wider variety of plants, most of which can’t use it.

The potential disadvantage for both oligolectic bees and their plant hosts is that if either one becomes rare, its partner could become rare, too. A spiraling decline of both bees and plants happens when, for example, a plant population is displaced by an invasive species or fails to thrive in a warmer or wetter environment. As the plant becomes less abundant, so does the oligolectic bee that depends on it. In turn, as the oligolectic bee becomes less abundant, so can the plant that depends on it for pollination. If fewer seeds are produced, the population may decline further, with consequent effects on the oligolectic bee, and so on. It’s a vicious circle that can be difficult to interrupt.

The Habitat Solution

Difficult but not impossible. The answer is to provide habitat, including preferred host plants, for the sunflower mining bee and other oligolectic species. Fortunately, there are several resources to learn which plants or groups of plants benefit which bee species.

Entomologist and ecologist Jarrod Fowler compiled a list of bee specialists documented in the Central U.S., a region that includes Minnesota, Iowa, Wisconsin, North Dakota, and South Dakota (3). He also tabulated their preferred plant(s) and found that species in the aster or sunflower family, Asteraceae, and the bean or pea family, Fabaceae, were visited most frequently by specialist bees in this region.

In addition, he noted the top 25 genera that support oligolectic bees. The genera found in this region include Helianthus (sunflowers), Heterotheca (false goldenasters), Solidago (goldenrods), and Symphyotrichum (asters).

Although Helianthus is a favorite of sunflower mining bee, the insect has also been collected from the flowers of (l to r) cup plant (Silphium perfoliatum), New England aster (Symphyotrichum novae-angliae) and goldenrod (Solidago) species, here showy goldenrod (S. speciosa).(1)

The Minnesota Department of Natural Resources’ Minnesota Bee Species List is another useful resource (5). The list of around 460 bees includes both those that collect pollen and those that are parasites on other bees’ nests. For those that collect pollen, the table provides the species’ lecty (range of pollen preference, either oligo- or poly-) and its nesting habitat, if either is known.

The species list in the Minnesota Statewide Bee Survey (2) includes not only the bees’ names and lecty, if the latter is known, but also the ecological province(s) where each species was found. The report includes distribution maps of the bee species as well as their conservation status, or S-rank, which can range from S1 (critically imperiled) to S5 (secure).

The 2024 Featured Plant series from the Board of Water and Soil Resources (6) highlights several plants that support specialist bees or other insects. A Featured Plant is posted online at the beginning of each month.

If you observe and photograph bees visiting plants, consider submitting your records to iNaturalist. Several bee-related projects are hosted on this online platform, including Minnesota Native Bees. To find other projects, go to the iNaturalist website, choose Projects from the Community drop-down menu, and type “bees” into the search box.

Who knows, maybe the sunflowers you watch this summer and fall will host sunflower mining bees. Although the bees were uncommon to rare in the state’s bee survey, you could be the lucky one who spots this specialist pollinator.

References

1)  Andrena helianthi, Robertson 1891. Discover Life. Website accessed July 3, 2024.

2)   Minnesota Statewide Bee Survey 2014-2023. Minnesota Department of Natural Resources.

3)   Pollen Specialist Bees of the Central United States. Jarrod Fowler, 2020.

4)   Dharampal, P.S., Hetherington, M.C., and Steffan, S.A. 2020. Microbes make the meal: oligolectic bees require microbes within their host pollen to thrive. Ecological Entomology 45: 1418-1427. DOI: 10.1111/een.12926. https://par.nsf.gov/servlets/purl/10253224

5)    Minnesota Bee Species List. Minnesota Department of Natural Resources, August 2023.

6)     Board of Water Resources Featured Plant series, 2024. (Red-berried elder is the July featured plant; plants featured in earlier months are in the Featured Plant archive.)

Plant Profile: Wild Ginger

A single flower emerges between a pair of leaves of wild ginger, Asarum canadense.

In spring, wild ginger is one of the first plants to emerge on the deciduous forest floor. Softly hairy leaves grow in pairs from shallow rhizomes, eventually expanding into heart- or kidney-shaped blades 3-5 inches wide. Mature petioles, or leaf stalks, are several inches long, and like the leaves, they are finely white-hairy. To an imaginative observer, they resemble pipe cleaners.

A single, reddish-brown, tubular flower develops in the axil of each pair of leaves. The flower is close to the ground on a slightly bent peduncle, or flower stalk. The flower has no petals, but its three, long-pointed sepal resemble petals and curve back over an open floral cup.

Inside the cup, the stigmas – the parts that receive pollen – mature first. They’re in the center of the flower, supported by their styles and surrounded by 12 stamens. Initially the stamens bend down and away from the stigmas, their pollen-bearing anthers lying parallel with the bottom of the cup. Over several days, the stamens straighten.

This dissected flower shows a central column of several upright stamens (solid arrow) surrounding stigmas and styles, which are hidden. The whitish dust around the top of the column is pollen. Several anthers still rest on the bottom of the cup (dashed arrow). 

Left: A flower with most stamens upright and a few still lying on the bottom of the floral cup.
Right: An older flower with all stamens upright.

A Pollination Puzzle

Pollination is a bit of a mystery. Many general references say the flowers are pollinated by flies and ground beetles attracted to the flowers’ fleshy color and supposed rotting-meat odor. As it turns out, that’s an assumption passed from one reference to the next, but it’s easy to see why it persisted.

Wild ginger doesn’t look like something pollinated by bees or butterflies. Although the flowers are beautiful in their details, they’re generally drab and mostly hidden under the leaves. They don’t look anything like the brightly colored, conspicuous flowers typically pollinated by bees or butterflies. Instead, their maroon to brown color matches that of animal flesh, like the flowers of some other plants pollinated by flies.

The bright yellow flowers of marsh marigold (Caltha palustris), left, are typical those pollinated by bees and other insects. The flower structure of skunk cabbage, center, looks and smells like decaying animal flesh and is pollinated by flies. Wild ginger, right, more closely resembles a fly-pollinated flower, at least in color. Photos not to scale. Skunk cabbage photo © 2009 Katy Chayka at Minnesota Wildflowers, used with permission granted on the website. 

Skunk cabbage (Symplocarpus foetidus), another Minnesota native, is a good example. It emerges in late winter or very early spring, even while snow covers the ground. Its flowering structure is a reddish-brown, leaf-like spathe enclosing a club of flowers called a spadix. As the plant’s name suggests, the structure has a fetid, dead-skunk smell. The small flowers on the spadix are pollinated by flies and beetles drawn to the plant’s carrion-like color and odor.

Other Evidence

Wild ginger doesn’t smell that bad. A sniff test finds that, at worst, the flowers can have a slightly unpleasant odor, but they don’t smell so strongly of rotting carcass that you would recoil. “Earthy” might be the best word to describe it. Some even say the flowers have a sweet smell. In any case, they aren’t obvious fly bait.

Early studies of wild ginger find other contradictions with the fly-pollination hypothesis. In the late 1940s, Harvey E. Wildman of the University of West Virginia experimented with wild ginger flowers to answer the question of how they’re pollinated (1). He removed the stamens from one group of flowers and left another group intact. In each group, he covered some of the flowers in wax paper bags (after ensuring no insects were inside the flowers) and left others uncovered. After several weeks, he checked the flowers for seed development.

None of the flowers with stamens removed, even those that were uncovered, developed seeds. In fact, all such flowers he checked had either fallen off or withered. In contrast, most of the flowers left intact developed “sound seeds.” That includes the ones that were covered. Wildman also reported that few insects were found inside any of the flowers.

If the flowers were strictly cross-pollinated by flies or other insects, at least some of the uncovered ones without stamens would have developed seeds, because something would have brought pollen to their stigmas. At the same time, the intact, covered flowers would not have developed seeds, because insects did not have access. Wildman concluded that wild ginger is primarily self-pollinated, not cross-pollinated.

Timed for Cross-Pollination?

Although Wildman’s experiment is illuminating, pollination is still a head-scratcher. One way plants foster cross-pollination is by staggering the development of stigmas and anthers inside a single flower, and wild ginger does exactly that. As mentioned above, the stigmas mature first, Eventually the filaments and anthers straighten and approach the stigmas, but not before the flowers have had a chance to receive pollen from another plant. This suggests that self-pollination is a back-up rather than a primary means of fertilization. Are we missing a pollinator? 

Whether self-pollinated or somehow cross-pollinated, fertilized flowers later develop seeds within capsules. When the capsules open in mid-summer, they expose small seeds with tiny fat bodies attached. The bodies, called elaiosomes (e-LY-oh-somes or e-LAY-oh-somes) attract ants, which carry the seeds back to a nest, eat the elaiosomes or feed them to their young, and leave the seeds to germinate, safely out of reach of seed predators. Seeds can also fall next to the parent plant and germinate there.

Left: The swollen ovary at the base of the flower indicates that this flower has been fertilized. Center: The same flower viewed from above. Each of the twelve dots around the center is what remains of a stamen. Right: Seeds are released in mid-summer. Each is just a few millimeters wide and long, with a golden-brown elaiosome attached. 

Rhizomes for Spread, Not for Spice

A rhizome of wild ginger (arrow).

If its seeds don’t succeed in helping wild ginger reproduce, its rhizomes can. (See the previous post for more about rhizomes.) The plant is almost aggressive in its vegetative spread, quickly filling suitable habitat, especially where it has limited competition.

Many say the rhizomes are aromatic and ginger-y in smell and taste. Although they have a long history of use as medicine and flavoring, ingesting them in any form is discouraged now. Wild ginger rhizomes and other parts have been found to contain variable amounts of aristolochic acid, a compound known to damage kidneys and perhaps cause cancer (2, 3). Handling the plants can also cause dermatitis.

This isn’t true of ginger roots (rhizomes) or ginger spice found in grocery stores. Culinary ginger is “true” ginger, Zingiber officinale, a tropical plant. It is not related to Asarum canadense.

Where to Find Wild Ginger

Wild ginger is native to deciduous and mixed deciduous-coniferous forests. It prefers full to part shade and moist, humus-rich soils. It wilts in prolonged drought. 

Wild ginger range in the upper Midwest and North America. Maps from USDA NRCS Plants Database (4).

Cited References

1)      Wildman, Harvey E. 1950. Pollination of Asarum Canadense L. Science 111 (2890): 551. http://www.jstor.org/stable/1676584.

2)      McMillin, D.L., Nelson, C.D., Richards, D.G., and Mein, E.A. 2003. Research Report: Determination of Aristolochic Acid in Asarum canadense (Wild Ginger). Meridian Institute.

3)      Qingqing Zhou, et al. 2023. Overview of aristolochic acid nephropathy: an update. Kidney Res Clin Pract 42 (5): 579-590.

4)      USDA, NRCS. 2024. The PLANTS Database (http://plants.usda.gov, 05/01/2024). National Plant Data Team, Greensboro, NC USA.

Other References and More Information

Anderson, M.K. Ed. 2000, 2003 and 2006. Plant Guide: Canadian Wildginger. USDA NRCS National Plant Data Center, Davis, California.

Baskin, J. M., & Baskin, C. C. 1986. Seed Germination Ecophysiology of the Woodland Herb Asarum canadense. The American Midland Naturalist, 116 (1), 132–139. https://doi.org/10.2307/2425945

Dunphy, S.A. Meadley, K. M. Prior, and M.E. Frederickson. 2016. An invasive slug exploits an ant-seed dispersal mutualism. Oecologia 181: 149-159. DOI 10.1007/s00442-015-3530-0 .

Hayden, W. John. 2010. Don't Judge a Book by its Cover: The Curious Case of Wild Ginger Pollination. Bulletin of the Virginia Native Plant Society 29 (1): 1, 6.

Schultz, K. 2014. Using shade to propagate Canadian wild ginger (Asarum canadense L.) and other woodland forbs. Native Plants Journal 15 (3): 231-235. DOI: https://doi.org/10.3368/npj.15.3.231.

Stritch, L. No date. Plant of the Week: Wild Ginger (Asarum canadense L.). USDA, US Forest Service.