Plant Profile: Ghost Plant, Monotropa uniflora

 This forest native has no chloroplasts and can't photosynthesize. How does it survive? By cheating.

Ghost Plant, Monotropa uniflora L.

Ghost Plant, also called Wax Plant, is well named. It looks like something fashioned, if not out of ether, then out of a chunk of paraffin and an active imagination.

Resembling a fungus more than a flowering plant, its pale, waxy stems and scaly leaves have no chloroplasts. They were lost somewhere along the plant’s evolutionary pathway, yet it manages to survive without being able to make sugars by photosynthesis. At first Ghost Plant was thought to be saprophytic, absorbing nutrients from decaying organic matter in its surroundings. That’s what fungi do, and it made sense that this plant, so similar in appearance, would do the same.

Each stem bears a nodding flower. 

From Partner to Parasite

Scientists then found that its roots, like those of most plants, don’t work alone. They are covered with and invaded by fungi, beneficial partners that reach farther into the soil to collect and transport nutrients, especially nitrogen and phosphorus, back to the plant.

These associations between fungi and roots, called mycorrhizae (MY-co-RY-zee, literally “fungus roots”), typically benefit both partners. The plant receives nutrients gathered by the fungus, and the fungus receives photosynthate made by the plant. It’s a textbook example of mutualism, a type of symbiosis in which both organisms gain something from their relationship.

Ancestors of Ghost Plant might have started out that way, with both the plant and the fungus sharing something with the other. Somewhere along the line, though, the relationship changed.  When Ghost Plant lost its chloroplasts, it could no longer give photosynthate to its fungal partner. The two-way relationship became one-way, and Ghost Plant behaved more like a parasite.

As a result, some of those fungal partners probably dropped off. With nothing to feed them, the fungi don't benefit from the relationship, and their association with Ghost Plant likely dwindled from a diverse many to a select few that either best met the plant’s needs or that failed to detect the ruse and avoid becoming hosts (1).

Tapping the Connection

Ghost Plant’s mycorrhizae are now associated only with fungi in the genus Russula, a group of mushroom-forming decomposers found all over the world (2). Russula also forms mycorrhizae with other plants -- green plants, plants that photosynthesize and send sugars to the fungus and then to Ghost Plant, if it’s joined to the same network.

Like tapping into a phone conversation, Ghost Plant takes some of what’s exchanged – in this case, sugars and nutrients – to support itself, without giving anything in return. It’s an adaptation that helps the plant survive in the deep shade of forest interiors. No need to grow tall or early or to develop leaves that can tolerate shade. Just plug into the web of connections between plants and fungi and take what’s needed.

The technical term for this is myco-heterotrophy, “myco” meaning fungus and “heterotroph” referring to organisms that feed on others. Ghost Plant is one of only 400 or so plants around the world that are fully myco-heterotrophic, meaning they spend their entire lives feeding on others through mycorrhizal connections (1).

Some scientists simply call the plant a parasite, either on the fungus or on the green plants connected to it. Others, citing the plant’s pickpocket habit, choose a more colorful term: Cheater.

Description and Range

Ghost Plant emerges and flowers in late summer. Each hooked stems bears a single flower at its tip. After flowering, the stems straighten and develop capsules full of tiny seeds. For more help with identification, see the Minnesota Wildflowers page for this species.

After flowering, the stems straighten and the flowers later develop capsules (right) with many seeds.

In Minnesota, Ghost Plant is mostly a northern species, but it’s also found in scattered counties in the south. It also grows in most of Wisconsin and generally in forests throughout the U.S. and Canada. According to Nature Serve Explorer and the Global Biodiversity Information Facility, Ghost Plant is also found in Central America, South America, Europe and Asia.

Cited References

1) Merckx, V., Bidartondo, M.I., Hynson, N.A. 2009. Myco-heterotrophy: when fungi host plants. Annals of Botany 104 (7): 1255-1261. doi: 10.1093/aob/mcp235

2) Massicotte, H.B., Melville, L.H., and Peterson, R.L. 2005. Structural features of mycorrhizal associations in two members of the Monotropoideae, Monotropa uniflora and Pterospora andromedea. Mycorrhiza 15: 101-110. DOI: 10.1007/s00572-004-0305-6

Additional References

Dance, A. 2017. Inner workings: Special relationship between fungi and plants may have spurred changes to ancient climate. Proceedings of the National Academy of Sciences USA 114(46): 12089-12091. Accessed online on 9/12/22 at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5699097/.

Van der Heijden, M.G.A., Martin, F.M., Selosse, M.-A., Sanders, I.R. 2015. Mycorrhizal ecology and evolution: the past the present, and the future. New Phytologist Foundation 205 (4): 1406-1423.  https://doi.org/10.1111/nph.13288.

Plant Profile: Wild Cucumber

This native vine is aggressive but not invasive in North America. The story is different overseas.

Wild Cucumber, Echinocystis lobata (Michx.) Torr. & A. Gray. This vine was growing over vegetation in a wet prairie.

Wild Cucumber, also called Wild Balsam Apple, is a native, annual vine of riverbanks, lakeshores, wetland edges and damp forest edges. It’s especially evident in late summer, when its long vines produce upright racemes of white flowers. (See Flower Parts for Plant ID for an explanation of racemes and other inflorescences.)

The vines are fast-growing, even aggressive, and where several get started, they can swamp whatever they’re growing on, including other plants. The sight of them covering a tree, shrub, or garden can be alarming – some say creepy – but according to the experts, there’s little to fear.

In late summer, Wild Cucumber produces upright racemes of white flowers. Staminate (male) and pistillate (female) flowers are separate, but on the same plant. To use the botanical term, the plant is monoecious (mo-NEE-shus).

Because Wild Cucumber is a native plant, it’s had a long time to fit in. Throughout its natural range in most of the U.S. and Canada, it’s adapted to the other things it lives with, and they are adapted to it. The vines may overgrow and perhaps smother its host plants, but because of these mutual adaptations, overall, Wild Cucumber is not considered a threat.

A soldier beetle collecting pollen from staminate flowers.

In other words, although Wild Cucumber can be aggressive, it’s not invasive. The latter term is reserved for plants (or animals) that are both introduced and aggressive. They’re new to an ecosystem, and for a variety of reasons, they have a competitive advantage. For example, they may grow fast, reproduce prolifically, have extended growing seasons or have few pests and diseases, so they can easily displace other plants and disrupt ecosystems.

That isn’t happening here, but in Central Europe, Wild Cucumber is a pest. In Hungary, Poland, Austria and other countries, Wild Cucumber was introduced as an ornamental and escaped cultivation. It has invaded rivers valleys, lakeshores and wetlands, forming dense mats that block light from reaching native European plants. By 2014, the plant had become such a problem that it was considered “one of the 100 most dangerous invasive plant species in Europe” (1).

It's possible to anticipate and even prevent such problems. Invasive plants have some characteristics in common, and studying them can predict how a plant will likely behave if it’s introduced outside its native range.

Here are some of the characteristics of Wild Cucumber that make it invasive in Europe (1).

• It has a broad native range
• It can adapt to a range of environments.
• It is a human commensal, meaning it benefits from association with humans.
• It grows fast.
• It reproduces in abundance, in this case by seeds.
• Its seeds remain viable for more than a year.

Many of the same characteristics are found in other plants that are invasive. Common Buckthorn (Rhamnus cathartica), for example, also has a broad range – across Europe – and can grow in several habitats. This shrub or small tree was brought to North America as a hedge plant and escaped. A female can produce hundreds to thousands of seeds, and they are viable for up to five years. Common Buckthorn forms dense stands that displace other plants, and it has become a scourge of many forested ecosystems.

By comparison, Wild Cucumber is mostly harmless, at least here. It will flower for a few more weeks before forming prickly, oval “cucumbers” that are not edible. The seeds will shoot out of the fruit in autumn, overwinter, and germinate in spring. That's a good time to remove the seedlings if you don't want them. Wild Cucumber is an annual, so the parent vine will die after one season.

For more information about how to identify Wild Cucumber, see this page from Minnesota Wildflowers. 

References

(1) CABI Invasive Species Compendium. Echinocystis lobata (wild cucumber). Accessed August 19, 2022. https://www.cabi.org/isc/datasheet/113998

How to Identify Native and Introduced Phragmites

Phragmites australis subsp. americanus. Photo taken in early August in southern Minnesota.

Update: An abbreviated ID guide (PDF) is here. 

Phragmites or Common Reed, Phragmites australis, is a 12- to 18-foot tall, perennial grass of wetlands, shorelines and ditches. Two subspecies are common in the U.S. One is the native subspecies americanus; the other is the introduced subspecies australis.

Both subspecies grow in colonies, but subspecies australis is more aggressive and can dominate habitats to the near exclusion of other plants. For that reason, there is growing interest in identifying and mapping subspecies australis to determine the extent of its spread and to target those colonies for removal.

Although the subspecies look alike, there are several characteristics that, taken together, can identify one from the other. The most reliable characteristics are shown below, after a few terms used to describe grass stems, leaves and flowers.

Stems and leaves

The culm is the stem of a grass. Grasses have round culms that are hollow between the nodes, the swollen areas on a culm. The leaf blade is flat and ribbon-like, whereas the leaf sheath wraps around the culm below the blade. Where the blade meets the sheath, most grasses have a ligule, a membrane or hairy fringe visible when the blade is pulled away from the culm.

Flowers

Grass flowers, called florets, are specialized for wind pollination. Each floret is composed of two narrow bracts, a lower lemma and an upper palea. Stamens and feathery stigmas emerge from between them.

Florets are arranged in small spikes called spikelets. At the base of each spikelet are two bracts called glumes. Glume length differs between the subspecies of Phragmites. More on that in a following section. 

Spikelets of Smooth Brome, Bromus inermis, are shown below. On the left are spikelets with brown anthers and feathery, white stigmas emerging from individual florets. On the right is a single spikelet spread apart to see the florets and glumes. The spikelets are about  3 cm (1.5 in.) long. 

Phragmites characteristics

To identify Phragmites subspecies, it’s best to look at more than one plant in a colony and at several characteristics of each plant. Hybrids are possible, but they’re said to be rare. 

Ligules 

To see ligules, pull back a blade from the middle third of the culm. (Ligules may be immature on the upper third of the culm and degraded on the lower third.) Ligule length differs between the subspecies. 

Subspecies americanus: 1-2 mm long, brown, become darker and smudgy in late summer and fall. The photo below was taken in early August.

Subspecies australis: 0.5-1 mm long, appearing as a thin, brown line. The photo below was taken in early July.

Stem color and texture

In summer and fall, examine the base of the culm. Be sure to look at the culm and not the sheath, if one is present. The photos below are from early July.

Subspecies americanus: Lower culm is smooth, somewhat glossy, often red.

Subspecies australis: Lower culm is ridged, not glossy, often green fading to brown.

Sheaths

In late summer, fall and early winter, examine the lower stem for the presence of leaf sheaths. The photos below are from mid-November.

Subspecies americanus: Sheaths are absent or easily removed.

Subspecies australis: Sheaths are persistent and harder to remove. 

Glumes

In late summer and fall, measure glume length. By late fall some of the florets may be gone, but the glumes often persist. It's best to look at several pairs of glumes to get an idea of their average length. The photos below are from mid-November.

Subspecies americanus: Lower glume 3-6 mm long (most > 4mm); upper glume 5-11 mm long (most > 6 mm).

Subspecies australis: Lower glume 2.5-5 mm long (most < 4 mm); upper glume 5-8 mm long (most < 6 mm).

Panicles

In late winter, spring or early summer, look at last season's panicles, the plume-like clusters of Phragmites spikelets. The photos below are from early July.

Subspecies americanus: Panicles bare, thinner, less branched.

Subspecies australis: Panicles fuzzier, thicker, more branched.

Look-alikes

Amur Silver Grass and Reed Canary Grass are two smaller grasses that can be mistaken for Phragmites. 

Amur Silver Grass, Miscanthus sacchariflorus, is an introduced grass that has silvery-white panicles in late summer and fall. It grows 6-8 feet tall, shorter than Phragmites, and its leaf blades have a white midrib. Its ligules are a greenish-white, hairy fringe. The photos below were taken in early August.

Amur Silver Grass plants and ligule.

Reed Canary Grass, Phalaris arundinacea, blooms in spring, not late summer, with smaller panicles that eventually contract. It's shorter than Phragmites, growing up to 5 feet tall. Its ligules are membranous and 3-8 mm long. 

Reed Canary Grass colony and ligule.

References

Chadde, S.W. 2012. Wetland Plants of Minnesota. 2^nd edition (revised). A Bogman Guide.

Judziewicz, E. J., Freckmann, R.W., Clark, L.G., and Black, M.R. 2014. Field Guide to Wisconsin Grasses. The University of Wisconsin Press, Madison.

Minnesota Aquatic Invasive Species Research Center (MAISRC). Identifying invasive Phragmites. Website accessed July 2022.

Swearingen, J., Saltonstall, K., and Tilley, D. Phragmites Field Guide: Distinguishing Native and Exotic Forms of Common Reed (Phragmites Australis) in the United States. Technical Note Plant Materials 56, October 2012. USDA Natural Resources Conservation Service, Boise, ID.

Plant profile: Enchanter's Nightshade

 

Enchanter's Nightshade, Circaea lutetiana L., in July. 

Enchanter’s Nightshade, Circaea lutetiana, doesn’t get a lot of positive attention. This native plant of the forest floor is often regarded as a weed, something to remove in favor of less aggressive, more attractive species. Its appearance is modest at best. Its name, though, suggests something less humble. What’s the story?

Mostly Inconspicuous

Compared to showier spring wildflowers, this summer bloomer isn’t much to look at. Individual stems grow up to a foot tall, sometimes longer, with opposite, egg-shaped leaves and smooth stems. The plant spreads with rhizomes to form colonies, especially in disturbed areas or canopy gaps where more light reaches the understory.

In July and August, Enchanter’s Nightshade produces small, white flowers on racemes. If not for their masses, the flowers would be easy to miss. Each is just a few millimeters across, smaller than an eraser on the end of a pencil, with a mere two sepals, two petals, two stamens and one pistil. They're beautiful, but minimal. 

Small, pear-shaped fruits follow. They’re covered with hooked hairs that grab onto anything that passes – shoelaces, socks, pants, fur. It’s impossible to ignore them, but it’s not the kind of attention that inspires admiration. A few steps through a patch catches a load of little stickers.

Flowers and fruits of Enchanter's Nighshade.

From Meek to Mythical

The ”enchanter” in the plant’s name is Circe, the sorceress of Greek myth. According to legend, she used herbs and potions to turn people into pigs, lions and wolves. One of the herbs in her concoctions was Circaea lutetiana, the plant that now bears her name. The species name lutetiana also reflects the plant’s supposed use in sorcery. Lutetia was the ancient city that is now Paris, France, called “the city of witches” in some accounts.

Studies of the plant’s chemistry don’t find much that is bewitching. Although it’s called a nightshade, it’s not a traditional member of that group. Nightshades are usually plants in the tomato family, Solanaceae (solan-AY-see-ee). In terms of chemistry, this family is known for its higher quantities of alkaloids, compounds that have uncertain roles in plants but a variety of physiological effects in humans. Some alkaloids, such as opium from poppies and cocaine from coca bushes, are mind-altering, euphoric and addictive.

In contrast, Enchanter’s Nightshade is in the evening primrose family, Onagraceae. Its chemistry features flavonoids, molecules that have various functions in plants. Some are pigments – the red of raspberries, for example – while others regulate growth or protect against UV radiation, among other roles (1, 2). Like alkaloids, flavonoids have potential use in medicine, but they aren’t mind-altering, and they aren’t associated with euphoria. In fact, they’re relatively benign. Circe might have worked some legendary magic, but Enchanter’s Nightshade wouldn’t have put much punch in her potions.

Adaptation and Potential Advantage

The ”nightshade” in its name, then, probably comes from its shady habitat. Like other plants of the forest floor, Enchanter’s Nightshade is adapted to an environment with limited light. One adaptation is its ability to colonize gaps or disturbances by growth if its rhizomes, underground stems that produce shoots along their length.

Unlike other clonal plants, Enchanter’s Nightshade holds some of that ability in reserve. Its new rhizomes do not produce shoots. Instead, they lengthen and branch until late summer, when some of them produce small tubers called hibernacles at their tips. Eventually the hibernacles are separated from the parent plant and from each other and go dormant. They are the vegetative equivalent of seeds, but with faster development the following spring to form patches of upright stems. In higher light intensities, this growth can be vigorous (3). 

Near the end of the season, tips of rhizomes (arrow) develop into tuber-like hibernacles.
The hibernacles overwinter and resume growth next spring, forming new rhizomes and
above ground shoots.

Although some consider that growth weedy and aggressive, it could prove useful. Restorationists are looking at Enchanter’s Nightshade and other “weedy natives” as potential cover crops where severe infestations of invasive plants have been removed. By shading out or otherwise competing with invasive plants that can reoccupy an area, Enchanter’s Nightshade may give native communities an improved chance to recover (4). 

It’s not magic, but it could be transformative. If research shows this to be an effective restoration technique, Enchanter’s Nightshade could help convert a landscape from diminished to diverse. 

References

(1) Falcone Ferreyra, M.L,  Rius, S.P., and Casati, P. (2012). Flavonoids: biosynthesis, biological functions, and biotechnological applications. Frontiers in Plant Science volume 33, article 222. https://doi.org/10.3389/fpls.2012.00222.

(2) Panche, A. N., Diwan, A. D., and Chandra, S. R. (2016). Flavonoids: an overview. Journal of nutritional science, 5, e47. https://doi.org/10.1017/jns.2016.41

(3) Verburg, R.W., and During, H.J. (1998). Vegetative propagation and sexual reproduction ­in the woodland understorey pseudo-annual Circaea lutetiana L. Plant Ecology 134: 211-224. https://doi.org/10.1023/A:1009741102627.

(4) Reinartz, J., White, M., and Hapner, J. No date. A role for native weeds and aggressive plants for replacing (or competing with) invasives in badly degraded areas. Invasive Plants Association of Wisconsin. Accessed online on 7/13/22 at A Role for Native Weeds - Invasive Plants Association of Wisconsin (ipaw.org).

Plant Profile: Bunchberry

 Cornus canadensis L.

Bunchberry, Cornus canadensis, flowering in northern Minnesota in mid-June 2022.

Also called Canada dogwood or creeping dogwood, bunchberry is a patch-forming, herbaceous plant of cool, moist forests. Although it’s related to red osier dogwood (C. sericea), gray dogwood (C. racemosa) and similar shrubs, this plant has no aboveground woody growth. Mature plants are just 3-6 inches tall, their short stems tipped by four to six, arc-veined leaves that are so closely spaced they appear whorled.

In late spring or early summer, mature plants produce a cluster of 12-40 small flowers surrounded by four white bracts. The petals of the flowers are just 1-2 millimeters long (1) and fused along their edges until they open.

The stamens of the flowers grow quickly, faster than the petals. As they mature, their anthers, the pollen-producing tips of the stamens, are trapped inside the closed flowers, but their lengthening filaments bend outward between the petals. Eventually, a trigger – a visiting bumblebee, for example, or the building pressure within the flower– causes the flowers to open explosively. As the petals flip back, the stamens spring outward, and pollen is catapulted into the air (2,3). The grains can be lofted as high as 2.5 centimeters (25 millimeters) above the flower, ten times the height of the flower itself (3).

A single bunchberry flower opens explosively -- in about half a millisecond (3). When the petals are flung back, stamens are released and catapult their pollen. Illustration based on photographs in Whitaker, et al. (2). 

[Watch a video of an exploding flower here.]

If they’re launched at high enough speed, some of the pollen may catch in the hairs of flying insects, which then carry it to other plants. Other pollen rides the wind. Unlike plants that are pollinated only by insects, bunchberry pollen grains are smooth instead of sticky, and so more easily carried by a breeze (2).

A dual system of pollination is an advantage for bunchberry. These low-growing plants are self-incompatible, so they need pollen from other plants to form seeds. If insect pollination isn’t successful, wind pollination might be, but for the latter to work, pollen must be launched high enough to be wafted over a patch of the plants.

If either method of pollination succeeds, the plants will produce bunches of red drupes, fruits with single, stony seeds. The fruits look like berries, inspiring the name bunchberry.

Where to find bunchberry

Bunchberry typically grows in cool, moist broadleaf, coniferous or mixed forests. In North America, its range is primarily the northern tier of states, all of Canada, and Greenland (4). This circumboreal plant is also found at northern latitudes in Asia.

More information

For photos and more information about bunchberry, see the Minnesota Wildflowers page for this species.

References

(1) Flora of North America, efloras.org. Accessed online on June 27, 2022. Formal citation: eFloras (2008). Published on the Internet http://www.efloras.org [accessed 27 June 2022]. Missouri Botanical Garden, St. Louis, MO & Harvard University Herbaria, Cambridge, MA.

(2) Whitaker, D., Webster, L., and Edwards, J. (2007). The biomechanics of Cornus canadensis stamens are ideal for catapulting pollen vertically. Functional Ecology 21. 219-225. DOI:10.1111/j.1365-2435.2007.01249.x

(3) Edwards, J., Whitaker, D., Klionsky, S. et al. 2005. A record-breaking pollen catapult. Nature 435, 164 (2005). https://doi.org/10.1038/435164a

(4) USDA, NRCS. 2022. The PLANTS Database (http://plants.usda.gov, 06/27/2022). National Plant Data Team, Greensboro, NC USA.

Does Garlic Mustard Eventually Decline?

One study found that it does, but it takes many years.

Garlic mustard, Alliaria petiolata, with flowers and maturing fruits in late May 2022.

Garlic mustard, the aromatic invader of forest understories and edges, has been here a long time. It first arrived in North America in the 1800s, when colonists likely carried it onshore to use as a medicine or potherb. Since then, it has spread from east to west, and now its invasive habits have landed it on many weed lists.

The lists inspire -- or require -- action, so each spring parties gather to pull out, cut off, or otherwise get rid of garlic mustard. It's easy where they've barely made inroads, but where populations are large and dense, removal takes many hours of stooping, kneeling, reaching and pulling. Then there's the additional commitment: Because garlic mustard seeds can remain viable in the soil for ten years or more, it's necessary to return year after year for monitoring and control. 

A less laborious solution would be welcome, and it may be emerging. A study led by Bernd Blossey at Cornell University found that although populations of garlic mustard initially increase, they eventually decrease (1). Is it best, then, to let nature take its course? Could garlic mustard's long residence be its downfall? Possibly, but many questions remain. 

Garlic Mustard Biology and Ecology

Garlic mustard is a biennial that produces rosettes the first year and flowering stems the second. Terminal clusters of small, white flowers bloom in April and May. Fruits are one- to two-inch long siliques -- narrow, linear pod-like structures that bear small seeds. One plant can produce hundreds to thousands of seeds. They are released in summer and germinate the following spring. 

At least on the leading edge of the population, growth is thick. Dense mats of seedlings grow into rosettes of similar cover, and after they overwinter, the plants bolt into a crowded stand of flowering stems. Fruits and seeds follow, and the cycle repeats as garlic mustard advances.

From left: A cluster of garlic mustard seedlings, a vigorous rosette, and a second-year, flowering stem.

Not every community is susceptible to a garlic mustard takeover. Although it's generally recognized as harmful, the magnitude of garlic mustard impacts depends on what else is present in the community -- which plants, animals, microbes and soils, for example, and how climate interacts with all of these. 

Vikki Rodgers, Sara Scanga and their team reviewed research since 2008 and teased out of that complexity a likely scenario for a successful garlic mustard invasion (2). First, earthworms and deer deplete populations of native plants. Less competition then gives garlic mustard an edge, and as it grows it further harms native plants through allelopathy, the release of compounds into the soil that harms other plants. Specifically, allelopathic compounds from garlic mustard disrupt the establishment of mycorrhizae, the associations between fungi and roots that help many plants absorb water and nutrients.  

Garlic mustard has the additional advantages of an extended growing season -- it begins in early spring, before most other species -- and prolific seed production. In a favorable location, all these characteristics appear to be an unbeatable combination. Time, however, could work against its dominance. 

Residence Time and Population Growth

The age of populations can also affect their staying power, and this is where Blossey's research comes in. From 2000 to 2006, he and his colleagues established 16 long term, permanent monitoring sites along garlic mustard's invasion trail, from states in the Northeast, where populations are older, to the Midwest, where they are younger. Each site was monitored for 5 to 15 years. 

At each location they set up quadrats (four-sided sampling plots) where twice a year they recorded stem or rosette density, stem height and percent cover. At the end of the study, they concluded that as residence time increases, garlic mustard populations become less able to sustain themselves. Although they are initially abundant, populations eventually decline until their growth rate falls below a level needed to maintain steady or increasing numbers. Overall, it took just over ten years to reach that point. 

According to Blossey, there are several possible reasons why this happens. Increasing residence time may help communities develop local biotic resistance, such as the buildup of parasites, diseases and insect herbivores that target garlic mustard. Garlic mustard decline was faster and greater in eastern study sites, which might be explained by regional differences in climate, soil and vegetation, three additional factors that could affect garlic mustard performance.

Blossey's team thinks that negative plant-soil feedback also plays an important role in garlic mustard decline. In a separate experiment, they found that the survival of garlic mustard rosettes was greater in soils that were not yet invaded or recently invaded, compared to soils that had "old" invasions of more than five years. In this experiment, at least, garlic mustard evidently creates or fosters soil conditions that work against its vigor in the long run. 

Call Off the Garlic Gangs?

Blossey points out that his research was possible only in areas where garlic mustard was not actively managed. Declines were observed in populations that were allowed to run their natural course and any interference could delay the development of biotic resistance, feedback mechanisms or other causes of garlic mustard's eventual decline. 

However, he also states that further long-term research is needed to answer questions that could determine if a hands-off approach is best. If garlic mustard eventually peters out, is the decline permanent, or will populations rebound? How fast can native communities recover after garlic mustard declines? Where garlic mustard is established, does it alone explain the impacts on native plants, or could other, more persistent, factors, such as deer or earthworms, contribute to the harm? 

Although not discussed in this research, questions of patience and acceptance are also important. Can people tolerate garlic mustard on their properties or in public parks, where they may be fostering or expecting to observe native communities? Are they willing to accept the advancing, dense growth of garlic mustard populations while they wait ten or more years for them to subside? Are there places where garlic mustard should be allowed to play out, and places where it shouldn't? 

The questions go on. Depending on the answers, it might be too soon to retire efforts to manage garlic mustard. More research is needed, especially long-term studies that include both land managers and research scientists. State or local laws may also have to be changed or exceptions granted to allow garlic mustard to grow unhindered. 

In the meantime, garlic mustard gangs have their work cut out for them. Some organizations offer contests and prizes for the most plants pulled. They might be the only occasions when a lot of garlic mustard is a good thing. 

References

(1) Blossey, B. et al. 2020. Residence time determines invasiveness and performance of garlic mustard (Alliaria petiolata) in North America. Ecology Letters 24(2): 327-336. https://doi.org/10.1111/ele.13649

(2) Vikki L Rodgers, Sara E Scanga, Mary Beth Kolozsvary, Danielle E Garneau, Jason S Kilgore, Laurel J Anderson, Kristine N Hopfensperger, Anna G Aguilera, Rebecca A Urban, Kevyn J Juneau, Where Is Garlic Mustard? Understanding the Ecological Context for Invasions of Alliaria petiolata, BioScience, 2022; biac012, https://doi.org/10.1093/biosci/biac012

Plant Profile: Wild Lupine

Wild lupine, Lupinus perennis

Wild lupine, Lupinus perennis, is at or just after its peak season of flowering at Crow Hassan Park Reserve. It's also called sundial lupine because its leaves are said to orient themselves to the sun.

This native of oak savannas and sandy prairies is a larval food source for the Karner blue butterfly, Lycaeides melissa samuelis, a federally endangered species. Wild lupine also supports at least seven other moths or butterflies as well as bumble bees, carpenter bees, mining bees and mason bees. See the reference to Heather Holm's book below.

In northeast Minnesota and parts of Wisconsin, bigleaf lupine, Lupinus polyphyllus, has become abundant and even invasive. Also called garden lupine, it was introduced from western states for ornamental use, and it is still available at many nurseries. Although it's valued for its colorful flowering scapes, its aggressive growth can displace native plants and pollinators. Bigleaf lupine does not support the Karner blue butterfly. 

The name "lupine" comes from lupus, the Latin word for "wolf." Lupine was once thought to deplete or "wolf" soils of minerals, but it does the opposite. Bacteria inside small nodules on its roots convert atmospheric nitrogen gas to usable form. When plant parts decompose, the soil is then enriched. 

References

Pollinators of Native Plants, by Heather Holm. Pollination Press LLC, Minnetonka, Minnesota. ISBN 978-0-9913563-0-0.

Oak Savanna Restoration for Karner Blue Butterfly. Minnesota Department of Natural Resources. Accessed June 12, 2022. 

Lupinus perennis (Wild Lupine). Minnesota Wildflowers Info. Accessed June 12, 2022. 

For the love of (wild) lupine. Tufts Pollinator Initiative, Tufts University. Accessed June 12, 2022.

Wild Lupine, Lupinus perennis. Illinois Wildflowers. Accessed June 12, 2022.

Lupinus perennis. Flora of Wisconsin, Wisconsin State Herbarium, UW-Madison. Accessed June 12, 2022.