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.

 

What is a rhizome?

Mayapple (Podophyllum peltatum) spreads by rhizomes. The two whitish nubs at the node in the middle are the beginning of shoots. Clusters of roots also grow from the nodes.

A rhizome (RY-zome), also called a creeping rootstock, isn’t a root at all. It’s a stem that runs roughly  horizontal under or just above the soil, producing roots and shoots along its length. Slender, aboveground rhizomes, like those of strawberries, are also called stolons (STOW-lons). In either case, they're stems, and they serve many purposes.

Rhizomatous (rhizome-bearing) plants are colony-formers. Mayapple rhizomes, pictured above, grow moderately fast to produce a steadily expanding colony. The compact rhizomes of large-flowered trillium (Trillium grandiflorum) grow much slower, producing closely spaced clumps of plants.  On the opposite end of the spectrum, weedy quackgrass (Elymus repens) and Japanese knotweed (Fallopia japonica) have vigorous rhizomes that quickly give rise to large, rapidly expanding colonies. That’s why they’re hard to manage. Even if they’re pulled or dug up, they can regrow quickly from even small bits of rhizomes left behind.

Left: A mayapple colony. Each plant is 12-16 inches (30-40 cm) tall. Center: Large-flowered trillium grows in clumps from slowly growing rhizomes. The flowers are about 2 inches (5 cm) wide. Right: The slender red rhizomes of wild strawberry (Fragaria vesca) are also called stolons. Each is about as wide as a pencil tip. 

Rhizomes have several benefits.

Rhizomes are a form of vegetative reproduction. Compared to flowers and seeds, they’re a faster and energetically less expensive way to grow a population. Rhizomes won’t spread a plant far and wide – seeds are often better at that – but if a plant is growing in a favorable place, rhizomes can increase its numbers quickly, and without the risk of losing fragile seedlings.

Except for stolons, rhizomes also serve as storage organs. As winter approaches, sugars and nutrients are moved underground, forming a protected reserve that can be tapped to begin next year’s growth. Some rhizomes end in tubers, swollen organs specialized for storage. Potatoes are a familiar example, but other plants also have tubers. The small tubers of native enchanter’s nightshade (Circaea lutetiana) detach from their rhizomes in fall and function much like seeds, and the tubers of yellow nutsedge (Cyperus esculentus), also called earth almonds, are the edible but maddening means by which this plant persists.

Left: Yellow nutsedge plants. Photo by Howard F. Schwartz, Colorado State University, Bugwood.org. 

Right: The thin, white rhizomes of yellow sedge bear small tubers. Photo by Steve Dewey, Utah State University, Bugwood.org.

Rhizomes have potential drawbacks, too.

Plants that produce seeds or spores combine DNA from different individuals to make genetically unique offspring. The young plants aren’t exactly like their parents or even like each other. In contrast, rhizomes produce genetically identical offspring. All shoots from a common rhizome are the same as their parents and the same as each other. In other words, they are clones.

If that uniform gene combination is adaptive in a certain environment, it’s an advantage. It’s like using the same, tried-and-true recipe over and over again, with great success. If conditions change, though, uniformity can be a drawback. If the plants don’t have the genetic makeup to adapt, say, to warmer or drier weather or shadier or lighter conditions, the population may not survive. Their genetic recipe may not serve them well anymore. Especially in a rapidly or drastically changing environment, plants that reproduce primarily by rhizomes may decline, while plants that reproduce by seeds or spores may survive if a few individuals have the genetic ability to adapt.

How to recognize a rhizomatous plant

In the field, there are several ways to know that a plant has rhizomes. One is to look for spreading growth. The presence of colonies can indicate that rhizomes lie below, although some plants without rhizomes also grow in spreading patches. They may have sprawling stems, for example, or seeds that land close to the parent plant.

Another option is to look underground. If possible and permissible, pull or dig up a stem and look at the root system. Rhizomes, if present, will grow horizontally or almost so. They will also have nodes, places where small, scale-like leaves are or were attached. That’s how to tell rhizomes from roots, which also grow from rhizomes. Some rhizomatous plants also produce aboveground leaves -- see the last section for an example. Wear gloves when you handle rhizomes; some can irritate skin or even cause poisoning if ingested. 

Canada goldenrod (Solidago canadensis) has pencil-thick rhizomes and much thinner and more numerous roots.

Left: Bloodroot (Sanguinaria canadensis) plants grow in slowly expanding colonies from their rhizomes. These plants, photographed in early spring, will eventually unfold their leaves and open their flowers. Right: A mature bloodroot rhizome is about as thick as a thumb. If cut it will "bleed" an orange-red latex. So will the aboveground parts. The latex is poisonous in large doses. Photo by Joseph O'Brien, USDA Forest Service, Bugwood.org.

A thorough plant guide will tell you if a plant has rhizomes. A plant’s name can be another clue. If the  common name includes “creeping” or “crawling,” it’s a good bet it has rhizomes. Creeping Charlie and creeping bellflower are good examples. Sometimes plants creep by other means, such as low-growing or arching stems that root at nodes where they touch the soil. This kind of creeping habit, though, can be easily spotted above ground.

Scientific names, too, can be revealing. Look at the specific epithet, the second word in a plant’s scientific name, which identifies the species. If you see repens or reptans, from Latin words meaning creeping or crawling, the plant likely has rhizomes. As mentioned above, the Eurasian import Elymus repens, or quackgrass, spreads aggressively by rhizomes. Native Polemonium reptans, or spreading Jacob’s ladder, also has rhizomes, but they grow slowly. The plant also spreads with its sprawling stems and self-seeding habit.

Looking for an easy rhizome to study? Try clover.

Introduced Dutch or white clover, Trifolium repens, is a convenient plant to see rhizomes. Its stem grows just above or below the soil, so it’s easy to pull up. This is the only stem the plant has. The vertical “shoots” are actually petioles, or leaf stalks, and scapes, structures that support clusters of flowers. Notice that the rhizome has nodes, but the petiole and scape do not. 

A white clover colony spreads by rhizomes. They can grow quickly, forming patches. 

True roots will also come up, and they lack nodes, too. Some of them may have tiny nodules attached. These aren’t tubers, but rather small bodies containing nitrogen-fixing bacteria. The bacteria convert nitrogen gas in the air to a form the plant can use. For more information about that, see The Boon of Biological Nitrogen Fixation.

A white clover rhizome and roots with nodules.

Look Closely at Wildflower and Pollinator Seed Mixes

If you’re thinking about sowing a wildflower or pollinator seed mix this season, you have lots of company.

Many people have been inspired to support pollinators by planting wildflowers to provide nectar and pollen. This increasing demand has spurred many companies to offer one or more seed mixes online or in retail stores. Caution is best, though, before choosing one. Look closely at the mix contents. “Wildflower” means different things to different people, and there could be surprises.

Consider the contents of this mix advertised for Minnesota:

Sweet William, Prairie Coneflower, Mexican Hat, Red Corn Poppy, Lance Leaf Coreopsis, Shirley Poppy, Wild Cosmos, Blanket Flower, Black Eyed Susan, Wild Perennial Lupine, Purple Coneflower, Russell Lupine, Plains Coreopsis, Siberian Wallflower, Scarlet Flax, Annual Red Phlox, Cornflower, Gloriosa Daisy, California Poppy, Perennial Blue Flax, Candytuft. 

Although these plants will likely survive in Minnesota, some are undesirable because they can grow aggressively, alter soil chemistry, or replace food sources that native insects or other animals are long adapted to using.

One example is Russell Lupine, also called Bigleaf Lupine. Known by the scientific name Lupinus polyphyllus, the plant is a garden favorite native to several western states. It has been introduced to the Upper Midwest, the Northeast, eastern Canada, and even Europe primarily for its ornamental value, but also for its deep, nitrogen-fixing roots that can stabilize and enrich soils.

In Minnesota, Russell Lupine has become especially abundant in the Arrowhead region, especially along roadsides through the north shore of Lake Superior. In spring and early summer, masses of the plants bloom in spectacular displays of white, pink, blue and purple. Their striking colonies are a big draw to that area each season. That’s good for the regional economy, but not so good for its environment. Beautiful though they are, the plants have some drawbacks.

Although Russell Lupine, L. polyphyllus, isn’t considered a noxious weed in Minnesota, the plant has several traits associated with invasive plants. It reproduces prolifically and grows in dense patches that exclude other plants, including native plants that have long supported pollinators. Although the plant declines in summer heat, it can grow in a range of other conditions, from moist to dry soils and full to part sun. That adaptability means it can grow in many habitats, from lakeshores and wetland edges to upland forest edges and roadsides. Its deep roots do help stabilize and enrich erodible, nutrient-poor soils – a useful trait for reclamation in the West – but deep roots also make the plant hard to remove from places where it isn’t wanted.

A mass of Lupinus polyphyllus along a roadside in northeast Minnesota. Photo copyright Peter Dzuik, 2004, and used with permission granted on the Minnesota Wildflowers website. 

Unfortunately, L. polyphyllus is sometimes mistaken for (and mislabeled as) our native “wild” lupine, Lupinus perennis. Now called Sundial Lupine to avoid confusion with “wild” Russell varieties, this perennial grows in prairies and savannas primarily in southeast and east central Minnesota and the eastern U.S.  

Like Russell Lupine, Sundial Lupine is beautiful, but more importantly it's critical for the survival of the federally endangered Karner Blue butterfly, Plebejus samuelis. Karner Blue larvae feed only on Sundial Lupine. Females lay their eggs on or near the plant – or what they judge to be the plant – and the caterpillars eat the leaves. Karner Blues are endangered in large part because Sundial Lupine has lost habitat, and as this larval host has become less plentiful, so has the Karner Blue.

Efforts are underway to bolster populations of Sundial Lupine, but where it overlaps with plantings of Lupinus polyphyllus, competition and hybridization present challenges. L. polyphyllus grows more aggressively and can displace L. perennis. The two species also hybridize, and unfortunately, neither L. polyphyllus nor its hybrids support Karner Blue larvae. If female butterflies lay eggs on either one, the larvae are unlikely to survive. 

Wildflower seed mixes, then, can include species that have both benefits and major drawbacks. To avoid problems like those caused by L. polyphyllus, it’s best to pause before choosing a mix. Study the contents and try to avoid species that can do more harm than good. Here are some steps to take:

• The surest and easiest solution is to buy seeds and seed mixes from a local native plant nursery. The Minnesota DNR maintains a list of native plant suppliers. These growers are familiar with what should and shouldn’t be included in a mix, but if you prefer to do the work yourself, keep reading.

• Look for scientific names of the plants in the mix. Different species may have the same common name, and plants with different common names may be the same species. Scientific names avoid this confusion by revealing a plant’s identity. If none are given, either don’t buy the mix or try to use the common names of the species to look them up.

• Using scientific names, search for information about each species. Where is it from? Does it have a reputation for invasiveness? Good sources include the USDA Plants Database, EDDMapS, the Invasive Plant Atlas, and your state’s department of natural resources. Alternatively, search online using the scientific name of the plant followed by “invasive.”  

• Be aware that plants native to the U.S. or North America are not necessarily native to your area. This may seem unimportant, but plants that come from another part of the country or continent can behave differently where they’re introduced.

• Also be aware that maps showing native ranges can be wrong. The USDA Plants Database map for L. polyphyllus, for example, shows that the plant is native to much of the U.S. and Canada. But a plant guide from the USDA states that it’s native only to several western states and two western Canadian provinces..

Range of Lupinus polyphyllus, according to the USDA. States and provinces
shaded green are where the plant is said to be native. Yellow stars are added to
show where the plant originated.

• As you read about the plant, look for invasive traits, such as rapid growth and prolific reproduction by seeds or vegetative parts. Phrases like “forms large colonies” and “naturalizes easily” are red flags, especially if the plant isn't native here. Comments from other growers can also be informative. One customer who grew Russell Lupine posted, “Lupines are growing everywhere, even the few seeds . . . tossed at the edge of the woods.” Sometimes pictures of a species provide a clue. If photos show an extensive carpet of plants (a monoculture), that plant is probably aggressive and could displace other species.

References and More Information

Wildflower and pollinator plantings

• Greta Gramig, Ph.D. Growing Wild: A ‘How-To’ Guide for Avoiding Weed-Filled Wildflower Mixes.  Weed Science Society of America.
•  Joe Baltrukonis. “Wild” Flower Seed Mixes: Buyer Beware! Ramsey Master Gardeners. April 23, 2021; updated June 24, 2021.
•  BWSR, The Nature Conservancy, Wild Ones, Xerces Society. How You Can Help Pollinators: Guidance for using pollinator seed in Minnesota home landscapes. BWSR.

 Russell Lupine, Lupinus polyphyllus

• Beuthin, M. 2012. Plant guide for bigleaf lupine (Lupinus polyphyllus). USDA-Natural Resources Conservation Service, Plant Materials Center, Corvallis, OR.
•  Dan Kraker. Invasive lupine, a lovely lightning rod on Minnesota's North Shore. MPR, July 1, 2022.
• Valtonen, A., Jantunen, J., Saarinen, K. Flora and lepidoptera fauna adversely affected by invasive Lupinus polyphyllus along road verges. Biological Conservation 133 (3): 389-396 (2006). https://doi.org/10.1016/j.biocon.2006.06.015.
• Prass, M., Ramula, S., Jauni, M. et al. The invasive herb Lupinus polyphyllus can reduce plant species richness independently of local invasion age. Biol Invasions 24, 425–436 (2022). https://doi.org/10.1007/s10530-021-02652-y
• USDA, NRCS. 2024. The PLANTS Database (http://plants.usda.gov, 01/28/2024). National Plant Data Team, Greensboro, NC USA.

Karner Blue butterflies

• Minnesota DNR. Plebejus samuelis: Karner Blue. Rare Speces Guide, MN DNR.
• U.S. Fish & Wildlife Service. Karner Blue Butterfly. USFWS.