The Burning Bush Story

Winged burning bush in a wooded understory. Its bright red fall color makes it easy to identify. 

Winged burning bush, Euonymus alatus, is beautiful in fall. Its vibrant orange to red-purple leaves are striking, and it has been widely planted for its burst of late-season color.

In Minnesota, however, the species and its cultivars are no longer available. Many homeowners and landscapers have been disappointed that the shrub is now considered invasive and is legally prohibited from sale. Some question this decision, saying that burning bush doesn’t spread to natural areas – not in great numbers, anyway.

What’s the story of burning bush? What evidence supports the claim that it invades natural areas? And if it does, what harm does it cause?

 

First Arrival

Winged burning bush is originally from northeast Asia, where it grows in forests, woodlands and shrub-dominated scrublands. Someone – it’s unknown who – introduced it into North America in the mid-1800s as an ornamental shrub prized for its winged stems, bright fall color and abundant red fruits (1).

Left: Burning bush in its blazing fall color. Center: Stems and older branches have corky wings. Leaves are opposite. Right: Reddish capsules open in fall to release seeds enclosed in bright red arils, or fleshy seed coverings.

By the early 1900s, burning bush had entered the nursery trade, and by the mid-1900s the shrub and its cultivars were well known. Plant catalogs from that time promote the plant’s fall color and attractive fruits. In 1934, Breck’s catalog included burning bush among several desirable shrubs, writing, “Those who enjoy having birds around their home will find no better way of attracting them” than to plant them (2).

In 1949, Adams Nursery wrote in its catalog, “No doubt one of the most conspicuous varieties in the autumn, with its brilliant scarlet foliage and fruits,” adding that one of the shrub’s cultivars is “[i]ndifferent to soil, shade, and city conditions.” In other words, it will grow just about anywhere it’s planted (3).

Other advertisements were similarly positive. Burning bush, they all said, is an ideal plant for a shrub border, foundation planting, specimen planting or other uses. At the time, there was no mention of it naturalizing.

Early Concerns

As burning bush became widely planted, observations of its unintentional spread started to accumulate. In 1973, botanists John Ebinger and Loy Phillippe published what may be the first documented observation of burning bush spreading beyond intentional plantings (4). During field work in Illinois, they found a sizeable, self-sustaining population of Euonymus alatus on a wooded hillside and valley. They wrote:

“The population studied dominates the understory in the more shaded parts of a north facing hillside and valley floor, being particularly abundant in small ravines. The entire population extends over an area of about 4 acres …. Numerous smaller plants and seedlings are also common.”

For the next 10 years, John Ebinger studied that site and documented what he found. In a 1983 report (5), he wrote that the burning bush population had expanded to 3 hectares (about 7.4 acres), with some plants more than 30 years old. Small plants and seedlings were still common. On the north-facing hillside, the seedling density was an average 138,500 per hectare (2.471 acres) and the density of saplings was an average 1,100 per hectare. On the ravine floor, the seedling density was an average 150,000 per hectare, and the density of saplings was an average 1,700 per hectare. He also noted that the population had almost doubled in number, and plants had spread to the forest edge and a nearby field.

About the plant’s invasive ability, he wrote, “Although not a major problem in natural areas, winged wahoo [another common name for Euonymus alatus] does have the potential to spread into good quality forests since it can grow and reproduce in dense shade. Most of the reproduction observed is from seeds falling from established plants. However, birds do regurgitate the seeds soon after ingesting them, and some seeds have been found to be viable after passing through the digestive tract.”

Later Decades

From the 1990s to the present, reports of naturalized burning bush have increased across North America. The greatest number are from the northeast US, but the plant is also spreading in the Midwest, including Minnesota. The map below is from EDDMapS, a reporting system for introduced plants that have become naturalized (6). Record density by county (or the equivalent in Canada) is indicated by color; the darker the shade, the greater the density.

 

Some of these reports are in or near natural areas, such as parks, forests, refuges and shorelands. For example, locations selected from the map above include Bedell Bridge State Park in New Hampshire, Griffy Lake Nature Preserve in Indiana, and Elroy-Sparta State Trail in Wisconsin. In Minnesota, burning bush has been reported in the Richard J. Dorer Memorial Hardwood State Forest, Great River Bluffs State Park, the Minnesota Valley National Wildlife Refuge and the Lower St. Croix National Scenic Riverway, among other places.

Some of these reports are of single plants or a few scattered individuals. Others document higher density populations or even monocultures. The photographs below are from a wood line between a private residence and the Richard J. Dorer Memorial Hardwood State Forest, where photographer Peter M. Dzuik noted full canopy closure by mature shrubs and nearly full cover of the ground layer by seedlings (EDDMapS report 5235347.)

 

Impacts and Intervention

Clearly, burning bush can be invasive. With enough time and in favorable circumstances, a few naturalized shrubs can turn into many, including in natural areas. Looking back, it’s not surprising that burning bush can spread. Some of the qualities that made it popular, namely its wide tolerance of growing conditions, its abundant fruit production and its ability to attract birds, are traits common to many invasive plants (7).

Those traits helped burning bush spread to many habitats, and where its cover is extensive and dense, its effects are significant. In its 2019 assessment of burning bush (8), the Minnesota Department of Agriculture’s Noxious Weed Advisory Committee (NWAC) concluded in part that burning bush and its cultivars can “aggressively displace native species through competition” and have “the potential to change native ecosystems” by forming dense thickets and ground layers. The NWAC also noted that burning bush invades not only forest understories but also prairies, pastures and coastal shrublands. (See question 8 in the Assessment Worksheet; it includes several references.)

As a result, the committee recommended adding burning bush to Minnesota’s Noxious Weed List in 2020, initially designating the species and its cultivars as Specially Regulated (9). After a three-year phase-out period, the plant was moved to the Restricted list, meaning it can’t be “imported, sold, or transported in the state” without a permit. It also means that burning bush has become so widespread in Minnesota that eradicating it or preventing it from reproducing isn’t realistic.

How To Identify Burning Bush

It’s easy to identify burning bush in fall, when its bright red-orange color and red fruits make it obvious. At other times of the year, its winged stems and opposite leaves (or buds) are helpful characteristics. A native burning bush (Euonymus atropurpureus), also called eastern wahoo or spindle tree, is found in southern Minnesota, usually in lowlands but sometimes in uplands (10). Its stems are squarish in cross section, with shallow ridges or faint lines along the angles. Unlike the stems of Euonymus alatus, they lack well-defined wings.

 

In late fall and winter, burning bush can be identified by its winged stems and red fruits.

For more information about either species, see these Minnesota Wildflowers pages: Euonymus alatus, Euonymus atropurpureus.  

References

1. Winged Euonymus (Euonymus alatus). iNaturalist. Website accessed November 15, 2025.

2. Joseph Breck & Sons., et al. 1934, Everything for Farm, Garden & Lawn. Joseph Breck & Sons, 1934, https://www.biodiversitylibrary.org/item/269483.

3. Adams Nursery. & Henry G. Gilbert Nursery and Seed Trade Catalog Collection. (1949). 100th anniversary, 1849, 1949. Adams Nursery, Incorporated. https://www.biodiversitylibrary.org/item/304370

4. New Plant Records for Illinois. John E. Ebinger and Loy R. Phillippe. Transactions of the Illinois State Academy of Science Vol. 66. No. 3 & 4, page 115.

5. Exotic Shrubs: A Potential Problem in Natural Area Management in Illinois. John E. Ebinger. Natural Areas Journal Vol. 3, No. 1. pages 3-6. 1983.

6. EDDMapS. 2025. Early Detection & Distribution Mapping System. The University of Georgia - Center for Invasive Species and Ecosystem Health. Available online at http://www.eddmaps.org/; last accessed November 23, 2025.

7. Exotic, Invasive Plants 101: Characteristics and Identification. Belinda Eshan. Natural Resources Conservation Service (NRCS) and Tennessee Exotic Pest Plant Council (TNEPPC). 2012.

8. Assessment Worksheet for Winged Burning Bush. Noxious Weed Advisory Committee, Minnesota Department of Agriculture. 2019.

9. Minnesota Noxious Weed List. Minnesota Department of Agriculture. Website accessed Nov. 11, 2025.

10. Trees and Shrubs of Minnesota. Welby R. Smith, Minnesota Department of Natural Resources. University of Minnesota Press, 2008. 

Spring ID of Bittersweet Vines

American bittersweet (Celastrus scandens) and invasive round leaf bittersweet (C. orbiculatus) are like identical twins: Only subtle differences tell them apart. 

This is especially true after their leaves have expanded and before they develop flowers. In this in-between time, the vines are practically impossible to distinguish. Both have twining stems with alternate, toothed leaves. Leaf shape is generally round, eliptical or egg-shaped with pointed tips, but their shapes are variable and overlapping. Even the name "round leaf" isn't much help to detect the invasive species, because its leaves aren't always round. 

In spring, though, two characteristics can help with ID: the way the leaves unfold or unfurl from the buds, called vernation, and how the flowers are positioned along the stem. 

Vernation

Inside the bud and as they begin to emerge, the edges of American bittersweet leaves are rolled inward, toward the upper side of the leaf. The botanical term for this is involute. In contrast, the leaves of round leaf bittersweet are folded vertically along the midvein, so the upper sides of the blade face each other. This is a conduplicate pattern. Depending on weather, vernation may happen quickly. Early observations are helpful. 

Left: American bittersweet leaves are involute -- they are rolled inwards in the bud and as they emerge. Middle and right: Round leaf bittersweet leaves are conduplicate -- intially, they are folded inward along the midvein. Photos by Lisa McIntire.

Flower Position

Bittersweet vines typically flower in May and June. The flowers of both vines are about 1/4 inch (5 mm) across and greenish white to greenish yellow with five petals. Male and female flowers are on separate vines.

The difference is the flowers' positions. American bittersweet flowers are clustered only at the ends of stems, whereas the flowers of round leaf bittersweet grow from leaf axils, the areas where leaves join stems.

American bittersweet flowers are clustered at the ends of stems and branches. No clusters grow from the axils. These are male (pollen-producing) flowers. Photo by Peter Dziuk, (c) 2011, from Minnesota Wildflowers. 

Unlike American bittersweet, clusters of round leaf bittersweet flowers grow from leaf axils. These are female (seed-producing) flowers. Photo by K. Chayka, (c) 2013, from Minnesota Wildflowers.

After flowering, male vines can't be identified to species using visible characteristics. Female vines, though, will develop fruits, and they are in the same positions as the flowers: American bittersweet at the ends of stems, round leaf bittersweet at the axils. 

The spherical capsules are initially green, but as the season progresses their walls ultimately turn either orange (American) or yellow (round leaf). In later summer and fall, the capsules split open to reveal red arils, fleshy berry-like structures that enclose the seeds. American bittersweet capsules contain only one seed; round leaf bittersweet capsules contain five. 

Left: Mature American bittersweet capsules are orange, later splitting to reveal red arils. Right: Mature round leaf bittersweet capsules are yellow. These have already opened. Both photos by Leslie J. Mehrhoff, University of Connecticut, Bugwood.org.

Why Early ID Is Important

Round leaf bittersweet is originally from Asia, introduced here for its colorful fruiting vines. It's more aggressive than native American bittersweet and will girdle and smother the trees it grows on. Its dense growth can shade out any plants below. The result is lower plant biodiversity, with consequent effects on insects, birds, and other animals. 

In Minnesota, round leaf bittersweet is listed as a noxious weed, and by law it must be prevented from spreading. Identifying the plant early, especially before it produces fruits, is important to contain its spread. More information is available from the Minnesota Department of Agriculture and the Minnesota Department of Natural Resources. 

Despite control efforts, round leaf bittersweet still finds its way into Minnesota. Seeds are dispersed by birds, and some online sellers will ship seeds or live plants into the state. Mistaken identity can be a problem, too. What's sold as American bittersweet is sometimes round leaf. Look at any photos on the seller's website and compare them to the pictures above. Better yet, if you want American bittersweet, buy it from a reputable, local native plant nursery.

If Round Leaf Bittersweet Is on Your Private Property

The Minnesota Department of Agriculture advises removing the vine but keeping it on your property to decay. Transporting it increases the possibility of fruits and seeds escaping.

If you have a wreath, spray or garland made from real fruiting vines, keep it indoors. Don't toss it outdoors, and don't throw it in the trash. Both will aid its spread. If you want to dispose of it and there is no other round leaf bittersweet on your property, take it to a composting site that accepts noxious weeds (call first) or enclose it in a clear plastic bag and put it in the sun for several weeks to months to kill any viable seeds. Crushing the seeds with a hammer may also be effective.

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.

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.

Battling Buckthorn: Research Continues

Common buckthorn, Rhamnus cathartica, fills the understory of this hardwood forest. Buckthorn retains its green leaves longer than most other woody plants.

Anyone who’s tried to manage invasive common buckthorn (Rhamnus cathartica) knows it’s a battle. Pull it out and seedlings take its place. Cut it and it grows back, especially if the cut stump isn’t treated with herbicide. Buckthorn baggies or other covers for cut stumps are an option, but not a practical one for large, dense infestations. The search for insects that target buckthorn hasn’t succeeded yet, either.

Although these difficulties are frustrating, researchers at the University of Minnesota haven’t given up. Just the opposite: They are leading several investigations of potential solutions. Their studies of biodiversity, fungi, goats and other possible buckthorn remedies are shedding light on what works, what doesn’t and what to try next. Here are summaries of some of their efforts.

Using biodiversity to control buckthorn

The University’s “Cover It Up!” studies investigate the use of plants to suppress regrowth of common buckthorn after it is removed. Two phases are completed and a third is in progress, all asking questions about which plants are best at outcompeting buckthorn, how best to plant them, and how managing fire and deer browsing affects the success of using plants to control buckthorn.

The researchers were surprised by one of their findings: Most buckthorn seeds remain viable in the soil for only 1-2 years, not the commonly thought 6 years. That means seedlings will be abundant for the first year or two after buckthorn is removed but should taper after that, assuming new seeds aren’t introduced.

Phase 3 of the project is underway. When it’s done, researchers hope to offer buckthorn solutions that are both affordable and practical. For more information, see the Cover It Up! project page.

Can fungi help?

In some parts of Minnesota and Wisconsin, buckthorn is dying, possibly from canker rot, root rot and other fungal diseases. Researchers are trying to identify the fungi infecting the trees and how they may be used to manage buckthorn stands. Employing fungi would reduce the use of herbicides, an important benefit when working near water or other places where protection of other resources is paramount. The project began in January 2023 and will continue for another two years. See the project website for more information and updates.

Orange growths of crown rust on common buckthorn.

Another fungus being investigated for control of common buckthorn is Puccinia coronata, the rust fungus that causes crown rust of oats. The fungus uses buckthorn as an intermediate host and is visible during summer as orange, fuzzy-looking spots on leaves and stems. Some negative effects of the fungus have been found on buckthorn, so researchers have started identifying those strains and studying their effects on buckthorn growth and mortality. The study began in January 2023 and continues for two more years. More information is on the project website.

What about goats?

A study to evaluate the effectiveness of goat grazing on buckthorn ended in 2021. Researchers found that although goats can control buckthorn, the benefit is temporary. Buckthorn can rebound after grazing unless other control measures follow.

Grazing goats are also at risk of eating snails or slugs that are intermediate hosts for the brainworm Parastronguloides tenuis, which can cause fatal neurological disease. Co-grazing waterfowl with goats has been suggested to reduce that risk, so the study also examined the effect of waterfowl on the abundance of snails or slugs. In a 2022 paper published in EcoHealth, the researchers found that where goats grazed alone, the abundance of snails and slugs increased, but where ducks and geese were included with goats, the increase didn’t occur. They also found that waterfowl didn’t affect the overall diversity of the snails and slugs, which is important to protect populations of native gastropods.

The researchers point out that while waterfowl can lower the numbers of snails and slugs and therefore reduce the risk to goats of acquiring brainworms, more study is needed to learn if this also reduces the incidence of the disease.

More challenges of goat grazing are discussed in this paper and several others linked at the project website.

Plant profile: Cow parsnip

Caution: The sap of cow parsnip and other members of the carrot family can cause skin rashes and blisters. See below for more information.

Cow parsnip, Heracleum maximum, is a big plant with a big name. This 4- to 8-foot-tall native plant of damp meadows and fields, streamsides, ditches, and low, open woods is named for Heracles or Hercules, the mythic Greek hero of superhuman strength. Even the species name, maximum, hints at its size. Few herbaceous plants are as robust.

A biennial or short-lived perennial in the carrot family, cow parsnip has alternate, divided leaves up to 2 feet across, with smaller, undivided leaves higher on the stem. The leaflets are irregularly lobed, coarsely toothed, and hairy. The petioles of lower and middle leaves are 3 to 10 inches long with sheaths where they meet the stem. Stems are stout, hollow, ridged, and hairy.

Lower leaves of cow parsnip are divided into three lobed, toothed leaflets. This leaf blade (left) is about 18 inches long. Petioles are long with sheaths where they meet the stem (right).

Cow parsnip flowers from late May into early July. Small, white, 5-petaled flowers are in flat-topped, compound umbels, clusters that resemble a collection of little umbrellas. (See Flower Parts for Plant ID to learn more about types of flowers and flower clusters, called inflorescences.) The flowers are pollinated by honeybees and many kinds of native bees and flies, the variety so great that some consider cow parsnip a pollinator magnet.

Cow parsnip flowers are arranged in compound umbels. Each spoke of the umbel extends to another, smaller umbel, called an umbellet. The tiny, white flowers have five petals. 

Fruits are flattened, up to 1/3 inch long and 1/4 inch wide, and brown with dark, vertical lines when they mature in late summer or early fall. They are winged on their edges and so can be dispersed a limited distance by wind. Eventually the fruits split apart and release two seeds. Cow parsnip reproduces only by seed.

These immature fruits of cow parsnip will turn brown when they mature in late summer.

Although the plant is native here and in much of North America, in some states it’s introduced and invasive. In North Carolina, for example, cow parsnip is described as aggressive and insidious and is classified as a noxious weed.

Be Careful

Cow parsnip is rarely considered an ecological problem here, but it should be handled with care. The leaves and stems contain furanocoumarins, compounds that sensitize skin to ultraviolet light. If skin is exposed to plant sap and then sunlight, blistering rashes may result. The condition, called phytophotodermatitis, can take weeks to heal. Always wear gloves, long sleeves and pants when handling this plant, and wash off and cover skin if exposed to the sap. The sap can also damage the eyes, so it’s best to wear eye protection if the plant will be disturbed.

Watch Out for a Look-alike

Giant hogweed (Heracleum mantegazzianum), a similar but much larger plant, is introduced and invasive. So far, this 10- to 15-foot-tall plant hasn’t been found in Minnesota, but it is present in Wisconsin, and it’s known to be especially hazardous. The Minnesota Department of Agriculture includes giant hogweed on its list of noxious weeds that should be eradicated if found. Report the plant’s location using Report a Pest or EDDMapS and handle it using extreme caution.

Invasive Plants in the Carrot Family

Cow parsnip isn’t one of Minnesota’s “bad carrots,” but several other species are, including not only giant hogweed but also wild parsnip, burnet saxifrage, Queen Anne’s lace, and several others. A guide to identifying these plants is available in the Downloads tab.

 

References

Friends of Eloise Butler Wildflower Garden

Minnesota Wildflowers

BWSR Featured Plant: Cow Parsnip

Illinois Wildflowers

USDA, NRCS. 2023. The PLANTS Database (http://plants.usda.gov, 06/21/2023). National Plant Data Team, Greensboro, NC USA.

Giant hogweed – Minnesota Department of Agriculture

Giant hogweed (Heracleum mantegazzianum) – Minnesota Department of Natural Resources

New Invasive Plants to Watch For

The Minnesota Department of Agriculture has added several new plants to its 2023 noxious weed list. This post focuses primarily on additions to the Prohibited-Eradicate category, but three other categories – Prohibited-Control, Restricted and Specially Regulated – are covered at the end of the post.

Prohibited-Eradicate: The Early-Detection List

The plants in this group either aren’t here yet or are present in low numbers. They're in the early-detection stage, when ideally, they can be found and removed before they become widespread. As the name of the group suggests, these plants should be eradicated by destroying all above- and below-ground parts. Transporting, propagating or selling them is illegal.

Three plants are new to the list this year: Johnsongrass, pale swallow-wort and red hailstone.

Johnsongrass
Sorghum halepense

USDA NRCS Plants Database (see references). Johnsongrass is
confirmed in counties shaded blue. Lakes and rivers are also
shaded blue.

This perennial grass was introduced to the U.S. in the 1800s as a forage crop. It is now found in many
habitats, including pastures, roadsides, ditches, old fields and wetlands. It reproduces by seeds and rhizomes and can spread aggressively to form dense mats that exclude other plants. It will not tolerate drought or extreme cold, so where winters are severe, Johnsongrass may be a facultative (optional) annual. Stressed plants can produce toxic levels of cyanide.

Johnsongrass grows 8-12 feet tall when flowering. Leaves are alternate, hairless and up to 2 feet long with white midribs. Ligules are 3-4 mm long, membranous and sometimes toothed. Johnsongrass flowers from mid-summer to fall in loose, purplish panicles.

Leaves of Amur silvergrass (Miscanthus sacchariflorus), another introduced plant, also have white midribs, but this plant is shorter at 6-8 feet. Its ligules are a hairy fringe, and its panicles are silvery and silky in fall.

Clockwise from left: Johnsongrass stem and dense stand by Chris Evans, University of Illinois, Bugwood.org; Johnsongrass rhizomes and panicle by Steve Dewey, Utah State University, Bugwood,org. 

Pale swallow-wort
Cynanchum rossicum (aka Vincetoxicum rossicum)

EDDMapS (see references). Pale swallow-wort is confirmed in
counties shaded green.The plant has also been confirmed in Ontario.

Pale swallow-wort, also called European swallow-wort, is a perennial, twining vine that was imported
to the U.S. in the late 1800s, probably as an ornamental. It thrives in disturbed sites but can grow in a variety of habitats, including fields, pastures and woodland edges and understories. Fast-growing and shade tolerant, it can quickly overrun and outcompete other plants. Because swallow-wort is in the milkweed family, female monarchs will sometimes lay their eggs on it if common milkweed is unavailable. There is concern, however, that swallow-wort is toxic to monarch larvae.

The vine has opposite, shiny, oval or heart-shaped leaves with pointed tips. Stems grow to 7 feet long, wrapping around other plants or structures for support or clambering over the ground. Sap is clear, not white. Clusters of pink to reddish-brown, star-shaped flowers bloom in June and July. Pods are slender, smooth and 2-3 inches long.

Black swallow-wort (Cynanchum nigrum) is also on the Prohibited-Eradicate list. It looks like pale swallow-wort but has dark purple flowers.

Clockwise from left: Pale swallow-wort vines by Rob Routledge, Sault College, Bugwood.org; Pods and seeds by Leslie J. Mehrhoff, University of Connecticut, Bugwood.org. Leaves and flowers by Rob Routledge, Sault College, Bugwood.org.

 

Red hailstone
Thladiantha dubia

EDDMapS (see references). Red hailstone is confirmed in 
counties shaded green. 

Also called golden creeper or tuber gourd, red hailstone is a perennial vine introduced to North America
in the late 1800s or early 1900s as an ornamental. This adaptable plant grows in abandoned fields, roadsides, gardens, crop fields, railroad corridors and natural areas. Red hailstone can quickly overgrow and smother other plants, including crops.

Vines grow up to 20 feet long with tendrils that grasp other plants or structures for support. Leaves are alternate and heart-shaped. Stems, leaves and petioles (leaf stalks) are hairy. Yellow, tubular flowers bloom from July to September on separate male (pollen-producing) and female (seed-producing) plants.

So far, all plants found in Minnesota are male, so the vines aren’t spreading by seed. Instead, they reproduce vegetatively by small tubers carried along waterways; many of the mapped infestations are along rivers or streams. Where both male and female plants grow, 2-inch oblong fruits may form on female vines. The fruits turn red when mature, thus the name red hailstone.

Before it flowers, red hailstone resembles other tendril-bearing vines in the same family. Wild cucumber (Echinocystis lobata) is a hairless vine with five-lobed leaves and white flowers that bloom in late summer. Bur cucumber (Sicyos angulatus) is hairy but also has five-lobed leaves. Its flowers are white or greenish-white. Neither cucumber vine has red fruits.

Clockwise from left: Red hailstone leaves and infestation by Katy Chayka, Minnesota Wildflowers; Red hailstone flowering plants by Peter Dzuik, Minnesota Wildflowers.

 

Clockwise from left: Red hailstone flowers by Peter Dzuik, Minnesota Wildflowers; male flower closeup by Katy Chayka, Minnesota Wildflowers; rhizomes and tuber by Katy Chayka, Minnesota Wildflowers.

Other Categories of Noxious Weeds

The MDA defines three other categories of noxious weeds. Two were expanded in 2023.

·         Prohibited-Control: Plants in this category are already established here, so eradication isn’t practical. Management aims at preventing them from reproducing by seed or vegetative organs, such as rhizomes, tubers or stem fragments that can take root. Transportation of all propagating parts is illegal except as allowed by state law, and the plants may not be propagated or sold in the state. Sixteen species are on the list, including three kinds of knotweed featured in a previous post, Are Psyllids the Solution to Invasive Knotweeds? No new species were added in 2023. 

·        Restricted: These plants are widespread in Minnesota. The only practical way to manage them is to restrict their importation, sale and transportation in the state, except as allowed by state law. Two plants are new to the list this year: lesser celandine (Ficaria verna), an aggressive spring ephemeral and garden escapee, and salt cedar (Tamarix ramosissima), also called tamarisk, a shrub first introduced in the West for landscape use, windbreaks and erosion control. 

·        Specially Regulated: These are native or nonnative weeds that are economically valuable but potentially harmful if not controlled. Three plants are new to the list this year. Amur corktree (Phellodendron amurense) now must be removed wherever females have been planted or escaped, or their fruits and seeds must be prevented from spreading. Only male cultivars are legal to sell. Production of Callery pear (Pyrus calleryana) is being phased out over the next three years, after which the tree will be moved to the Restricted category. Tatarian maple (Acer tataricum) and its cultivars can be sold only if a label is attached advising that they should be planted only where the seedlings can be controlled, and ideally at least 100 yards away from any natural area.

 

References

EDDMapS. 2023. Early Detection & Distribution Mapping System. The University of Georgia - Center for Invasive Species and Ecosystem Health. Available online at http://www.eddmaps.org/; last accessed March 20, 2023.

USDA, NRCS. 2023. The PLANTS Database (http://plants.usda.gov, 03/23/2023). National Plant Data Team, Greensboro, NC USA.

Johnsongrass

Wisconsin Department of Natural Resources

Minnesota Department of Agriculture

USDA Fire Effects Information System

University of Missouri

Pale swallow-wort

Minnesota Department of Agriculture

USDA Forest Service

Wisconsin Department of Natural Resources

Michigan Department of Natural Resources

Red hailstone

Minnesota Department of Agriculture

University of Minnesota Extension Service

Minnesota Wildflowers