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.

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.

Moonseed Vine: A Poisonous Grapevine Look-Alike

Moonseed vine, Menispermum canadense, in early fall. Although most of its leaves have now fallen, it can still be identified -- and avoided, if foraging.

Moonseed vine (Menispermum canadense), also called Canada moonseed, is a twining vine of deciduous forests and riverbanks, thriving in moist or mesic soils and partial shade. Although the vines have now shed their leaves, moonseed vine can still be identified by other characteristics, and for foragers of wild foods, the distinctions could be lifesaving.

The danger comes from mistaking moonseed vine for riverbank grape (Vitis riparia). Both vines produce clusters of deep blue or purple, spherical fruits that can remain on the vines through winter. Unlike edible grapes, however, moonseed fruits are poisonous.

That’s because moonseed vine contains alkaloids, compounds many plants produce for defense against herbivores. Although alkaloids have been and are used medicinally, they can also be poisonous. Several sources report that eating moonseed vine, especially the fruits and seeds, can be fatal because of its alkaloids. The Minnesota Poison Control System includes moonseed on its list of toxic plants and advises calling Poison Control if any part of the plant is eaten.

Fortunately, poisoning can be avoided. There are reliable ways to tell the difference between moonseed and riverbank grape, even in fall and winter. Here’s what to look for.

Seeds

Moonseed fruits contain single, flat seeds that look like crescent moons. In contrast, riverbank grape seeds are egg-shaped, and there are usually several inside each fruit. This photo from the University of Wisconsin shows them side by side. 

Twining vs. grasping vines

Moonseed is a twining vine. It clambers over other vegetation or climbs upward by wrapping its stems around small trees or shrubs. Riverbank grape is a grasping vine. It uses tendrils, modified leaves, to clutch onto supports and hold the vines upright. 

Twining stems of moonseed vine, left, and grasping stems of riverbank grape, right.

Stems and bark

The young stems of moonseed vine are brown or greenish brown and hairy, although as the stems age, they lose the hairs. Stems grow as large as 2 cm in diameter ( a little less than an inch) and have ridged or fluted bark. 

Younger stems of grapevine are brown or reddish brown and hairless. Mature stems grow up to 20 cm in diameter (about 8 inches) and have brown, shaggy bark.

Young moonseed stems, left, are brown or brownish green and hairy. Young stems of riverbank grape, center, are reddish brown and smooth. Mature stems of riverbank grape, right, are brown and shaggy. 

Leaf scars and buds

Leaf scars are marks on woody stems left by petioles when leaves are shed in fall. Inside them are small, often raised dots called bundle scars, created when strands of vascular cells (water- and food-conducting cells) are severed when leaves fall off the stem. Buds – next year’s protected growth – sit above the leaf scars.

The leaf scars of moonseed vine are typically 2-3 mm long and wide, oval to circular in outline, and concave. They are often notched or split at the top. Inside the leaf scar, the bundle scars are arranged in a faint, broken circle or oval. The bud is barely visible above the leaf scar; it appears to be embedded in the stem, protruding a millimeter or less above the surrounding tissue.

Leaf scar and bud of moonseed vine viewed from the front (left) and side (right). 

The leaf scars of riverbank grape are typically 2-4 mm long and wide and roughly triangular, semicircular, or U-shaped. The perimeter of the leaf scar may be ridged, but the leaf scar is not noticeably concave. To the side of the leaf scars are linear marks called stipule scars.(Stipules are thread-like or leafy structures at the bases of petioles in some plants.) Bundle scars are hard to see, but there are several. The bud is brown or reddish brown and 3-5 mm long. 

Leaf scar, bud and stipule scar of riverbank grape viewed from the front (left) and side (right).

Leaves, if still present

Both moonseed vine and riverbank grape have alternate, lobed leaves, but they have different margins (edges) and points of petiole attachment. These features can also be found on fallen leaves if they’re still intact.

The margins of moonseed leaves are smooth, although the lobes may have pointed tips. In addition, the petioles are attached inside the leaf blade, even if just barely, making a peltate or shield-shaped leaf blade. The leaves of riverbank grape are sharply and coarsely toothed, and the petiole is attached at the edge of the blade, at its base. 

Riverbank grape, left, has lobed, coarsely toothed leaves. Moonseed vine (right) also has
lobed leaves, but the margins are smooth, not toothed.

The petiole of riverbank grape, left, is attached at the edge of the blade. The petiole of
moonseed vine, right, is attached just inside the blade. 

Rhizomes and roots

Although aboveground characteristics are enough to positively identify moonseed and grapevine, belowground structures can also be helpful if it's possible -- and permissible -- to uncover or uproot them.

Moonseed vines have yellow rhizomes, underground stems that grow horizontally and produce roots and shoots along their length. Because of their color and traditional use to treat various ailments, Dakota Indians call it yellow medicine, the namesake of Yellow Medicine River and Yellow Medicine County in southwest Minnesota. The homeland of the Dakota is Pezihutazizi Kapi, “the place where we dig for yellow medicine.”

No source for this article describes grapevine as having rhizomes, but its woody, brown stems can become buried and grow roots at their nodes. These rhizome-like stems look nothing like the slender, yellow rhizomes of moonseed vine, however. 

The rhizomes of moonseed vine, left, are yellow. The roots and rhizome-like stems of riverbank grape, right, are brown.

Moonseed vine is found in much of Minnesota but is more abundant in the southern part of the state. Its broader range generally covers the eastern half of the US. The vine flowers in late spring and early summer. For more information, see the webpages from Minnesota Wildflowers and The Friends of the Wildflower Garden, Inc. Both are linked below.

Range maps of moonseed vine, from the USDA Plants Database.

Riverbank grape is also found in most of Minnesota except for several counties in the far north and northeast. More broadly, its range extends from the Mid-Atlantic states into New England and west through the Dakotas.

References

Minnesota Wildflowers

Friends of the Wildflower Garden

Oxford Plants 400

University of Wisconsin – Green Bay, Cofrin Center for Biodiversity Herbarium

Minnesota Poison Control System

USDA, NRCS. 2023. The PLANTS Database (http://plants.usda.gov, 10/14/2023). National Plant Data Team, Greensboro, NC USA.

Minnesota River Basin Data Center

Upper Sioux Community

Flinging Spores and Fern ID

The back of this lady fern frond (Athyrium filix-femina) is covered with sori, clusters of spore-forming bodies called sporangia. Each sorus holds dozens of them, all covered by a protective flap of tissue called an indusium. When a sporangium matures and dries, a line of cells over the top of the sporangium contracts, causing it to fling open and catapult its spores. You can watch it happen here in a sorus of an unidentified fern.

A spore print made by a lady fern frond. The spores are so small they look like dust. 

Unlike seeds, spores don’t contain embryonic plants. They’re little more than tiny packages of DNA that give rise to the next generation of ferns. They do this by first growing a small, heart-shaped prothallus, a body that produces egg and sperm cells. The flagellated sperm cells swim through a film of water to fertilize the egg cells, which then grow into the ferns we recognize. Because water is needed for this kind of reproduction, many ferns rely on damp or humid habitats.

Lady fern is identified in part by the shape of its sori. They are usually curved or
horseshoe-shaped. They appear in late summer and early fall.

Fertile fronds of ostrich fern.

Not all ferns have sori that look like those of lady fern. Some are located along the edges of the frond, some have indusia of different shapes or sizes, and some have no indusia at all. Other ferns, such as ostrich fern (Matteuccia struthiopteris) and sensitive fern (Onoclea sensibilis), produce spores on fronds specialized for that purpose – in other words, the whole frond is devoted to forming spores. For all these variations, timing is important. Sori and reproductive fronds (aka fertile fronds) may appear only at certain times of the year, and the appearance of sporangia and sori can vary depending on how old they are. 

Both reproductive and vegetative characteristics are helpful to identify a fern. Here are some resources to learn more about fern anatomy, biology and identification.

• Ferns. U.S. Forest Service. This site may take a few tries to load.
• Dichotomous Key to Ferns of Wisconsin, by Tim Gerber, UW-La Crosse.
• Key to Fern Traits, by Areca Treon. This is a key to ferns in Cedar Creek Ecosystem Science Reserve near Bethel, MN.
• Ferns of Minnesota, by Rolla Tryon. Illustrated by Wilma Monserud. University of Minnesota Press, 1980. ISBN 0-8166-0932-2.
• Ferns and Lycophytes of Minnesota: The Complete Guide to Species Identification, by Welby R. Smith (author) and Richard Haug (photographer). University of Minnesota Press, 2023. ISBN 1517914663.

 For more information about lady fern, try these sites:

• Minnesota Wildflowers
• Friends of Eloise Butler Wildflower Garden