Wax Plant in its Waning Days

 

These are the dried stems and capsules of wax plant (Monotropa uniflora L.). The capsules at the tops of the stems split open to release winged seeds no bigger than a millimeter. That’s about as big as the tip of a pencil.

Carried by wind to other places on the forest floor, the seeds will germinate only in the presence of certain fungi that help them grow. These fungi also connect to tree roots, forming associations called mycorrhizae (MY-co-RY-zee). It’s a mutually beneficial relationship. The fungi help gather nutrients for the trees, and the trees provide carbon (sugars) for the fungus.

Wax plant taps that connection. The plant isn’t photosynthetic, so to support its growth it diverts carbon and nutrients from mycorrhizal fungi into its own roots. Because it gives nothing in return, wax plant is a parasite on the fungus. Such plants are called myco-heterotrophs: They get energy and nutrition from fungi.

Being a myco-heterotroph allows wax plant to survive in deep shade. It doesn’t depend on sunlight – it has no chlorophyll to absorb light – so it can grow in dark forest interiors where there is little competition from other plants. The trade-off is its dependency on mycorrhizal fungi for much of what it needs to survive. The thread from tree to fungus to wax plant is both a lifeline and a liability.

More About Wax Plant

The name wax plant comes from the plants' white, waxy-looking stems. Other common names are ghost plant and corpse plant. It's also called Indian pipe from the resemblance of its curved flowering stems to Native American ceremonial pipes.

Although it's often mistaken for a fungus, wax plant is a flowering plant. In Minnesota, stems emerge in mid to late summer. Flowers are visited by a variety of insects, but they are pollinated primarily by bumblebees. After pollination the hooked stems straighten, darken, and develop seed-bearing capsules. 

The name Monotropa means “one turn,” referring to the nodding stems of the plants in bloom. The species name uniflora means “one-flowered.” Typically, each stem bears only one flower.

Wax plant grows in rich, forested habitats in much of North America. This circumboreal species also grows in Asia.

Garlic mustard (Alliaria petiolata), an invasive plant that can also grow in shade, could be harming wax plant and other myco-heterotrophs. Chemicals in garlic mustard are known to interfere with establishment of other mycorrhizal relationships, and they may be doing the same to wax plant.

References

Monotropa uniflora (Indian Pipe). Minnesota Wildflowers. Viewed November 11, 2021, at https://www.minnesotawildflowers.info/flower/indian-pipe.

DeLay, Chantelle. Undated. Plant of the Week: Ghost Pipe (Monotropa uniflora L.). USDA, U.S. Forest Service. Viewed November 10, 2021, at Ghost Pipe (fs.fed.us).

Monotropa uniflora Linnaeus. Flora of North America, Vol. 8. Viewed November 13, 2021, at Monotropa uniflora in Flora of North America @ efloras.org.

Volk, Thomas. 2002. Tom Volk’s Fungus of the Month for October 2002. Accessed November 13, 2021, at http://botit.botany.wisc.edu/toms_fungi/oct2002.html.

Klooster, M. R., & Culley, T. M. (2009). Comparative Analysis of the Reproductive Ecology of Monotropa and Monotropsis: Two Mycoheterotrophic Genera in the Monotropoideae (Ericaceae). American Journal of Botany, 96(7), 1337–1347. https://www.jstor.org/stable/27733466

Martine C.T. and Hale,  A.N. (2015.) Parasitism disruption a likely consequence of belowground war waged by exotic plant invader. Am J Bot. 2015 Mar;102(3):327-8. doi: 10.3732/ajb.1500025. Epub 2015 Mar 2. PMID: 25784465. Viewed 11-12-2021 at https://pubmed.ncbi.nlm.nih.gov/25784465/

How Did Bittersweet Nightshade Get Its Name?

Warning: Bittersweet nightshade is poisonous. Don’t eat it.

Bittersweet nightshade, Solanum dulcamara, takes part of its common name from its taste. Its leaves and stems taste bitter and then sweet as its chemical components break down. The species name dulcamara comes from that quality. It's a combination of the Latin root words dulc, meaning sweet, and amar, meaning bitter.

The origin of “nightshade” isn’t as clear. One explanation is that it comes from the narcotic effect of many plants in the genus Solanum. Bittersweet nightshade and its relatives contain solanine, an alkaloid that affects the nervous system. The solanine content of this plant is highest in its leaves and green fruits but eating any part can cause stomach upset, drowsiness, dizziness, delirium and in severe cases respiratory failure and death.

Less ominously, “nightshade” could also come from the shady habitats where these plants may grow. Another origin could be the black berries that some Solanum species produce. Bittersweet nightshade isn’t one of them – its fruits are red at maturity – but other nightshades are well known for their black fruits.

One of them is the highly toxic Atropa belladonna, commonly known as deadly nightshade or simply belladonna. The black berries of this plant are high in atropine, an alkaloid now used to dilate pupils for eye exams, treat low heart rates and counteract other poisons, among other medical uses. In earlier times, however, people used belladonna for other purposes, with some risk. During the Renaissance, Venetian women dropped diluted berry juice into their eyes to dilate their pupils, a look considered beautiful at the time. That effect is captured in the species name belladonna, meaning “beautiful woman.” 

There were darker uses for belladonna. Ancient Romans are said to have incapacitated or killed their enemies by contaminating their food supply with the plant, and stories abound of its use as an assassin’s poison. Accidental poisonings still occur from misuse of herbal products or ingestion of berries mistaken for blueberries or other edible fruits.

Bittersweet nightshade isn’t as poisonous as belladonna, but it’s still best to be cautious. Its name speaks of its chemistry and the long, sometimes perilous history of the nightshade group. Before grabbing a handful of its berries, heed its name. It says beware.

More about Bittersweet Nightshade

Also called woody nightshade or climbing nightshade, bittersweet nightshade is an
introduced vine now found throughout much of North America. It’s often associated with disturbed sites, especially those with wet or moist soils. Wetland edges, lakeshores, riverbanks, and deciduous forests are typical habitats. The vine grows up to twenty feet long, clambering over other plants or weakly twining around trees, shrubs or fences for support. In this region, bittersweet nightshade flowers from June to September. Fruits are oval, tomato-like berries about ½ inch long. They ripen from green to yellow, orange and eventually red. 

This introduced plant can be aggressive, especially in wet habitats that favor robust growth. It should be removed from places where children, pets or livestock may eat its leaves, stems or fruits.

Bittersweet Nightshade is in the family Solanaceae, a group that also includes tomatoes, peppers, eggplant and potatoes. Tomatoes, peppers and eggplants are edible fruits; they contain little or no solanine. Potatoes tubers are also edible unless they’re exposed to sun and turn green from chlorophyll. Chlorophyll isn’t poisonous, but it shows that solanine may have accumulated in the tuber and could cause illness.

References

USDA Forest Service. The Powerful Solanaceae. Solanaceae (fs.fed.us). Website accessed October 30, 2021.

Kandeler, R., and Ullrich, W.R. Symbolism of plants: examples from European-Mediterranean culture presented with biology and history of art: August: bittersweet, woody nightshade. https://www.cabi.org/isc/abstract/20093251708. Website accessed October 30, 2021.

Flora of Wisconsin. Solanum dulcamara. https://wisflora.herbarium.wisc.edu/taxa/index.php?taxon=8664. Website accessed October 29, 2021.

Waggy, Melissa A. 2009. Solanum dulcamara. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: https://www.fs.fed.us/database/feis/plants/shrub/soldul/all.html [2021, October 27].

Plant Profile: Brown-eyed Susan

 

Brown-eyed Susan, Rudbeckia triloba, is a rare find in the wild. Although this native annual or short-lived perennial grows throughout the eastern U.S., it reaches the northwest limit of its natural range in Minnesota. Here it’s a state-threatened species, documented in open woods and floodplain forests in a handful of counties in the southeast part of the state. Both habitats continue to lose ground due to land conversion and invasive plants such as common buckthorn, making a natural population of brown-eyed Susan an exceptional discovery.

Although wild populations of brown-eyed Susan are hard to find, intentional plantings are not. This late-summer bloomer is popular in gardens and naturalized landscapes across the state. It’s in its peak season of flowering in late summer, an ideal time to look for and identify this plant.

How to Identify Brown-eyed Susan

Brown-eyed Susan is easiest to recognize by its profusion of 1- to 2-inch-wide flower heads. Each head is a collection of small flowers called florets. The center of the head, called the disk, is a button-shaped, mounded or conical structure bearing dark purple to brown disk florets. Around the disk are 6-13 ray florets, small flowers bearing a single, yellow-orange, petal-like ray. The rays are grooved along their length and have small notches at their tips. Flowering is from August into October (2, 3, 4).

Brown-eyed Susan can also be identified by its leaves and stems. It’s a tall plant, commonly 2-4 feet but up to 5 feet, with reddish, bristly stems. The leaves are also bristly on both surfaces. The lower leaves often have three lobes, the source of the specific name triloba and another common name, three-leaved Rudbeckia. (The latter is a misnomer; lower leaves are three-lobed but are not divided into three leaflets.) The lobed, lower leaves are stalked, whereas the upper leaves are lance-shaped or elliptic with short or no stalks. Because the plant tends to branch widely, it can look bushy, but smaller plants have fewer branches.

As noted above, natural habitats are low, open woods and floodplain forests, but brown-eyed Susan also grows in the moist soils of thickets and stream banks (4). Favorable garden locations should provide sun to part shade and moist, loamy soils.

Look-Alikes

Black-eyed Susan (Rudbeckia hirta) and orange coneflower (Rudbeckia fulgida) are the most common look-alikes. Compared to either species, brown-eyed Susan is taller and more branched with reddish-green stems. Its flower heads are 1-2 inches across, smaller than other Rudbeckia species. Brown-eyed Susan also blooms later and longer into fall.

Sweet Coneflower (Rudbeckia subtomentosa) is also like Brown-eyed Susan. Its natural range barely extends into southeastern Minnesota from its broader range to the south and east. Like Brown-eyed Susan, it is a tall plant – up to 6 feet – and some of its leaves may be three-lobed. However, its flower heads are wider, 2-3 inches across, and both the leaves and the bracts below the heads are described as being dotted with glands (2). This may require a magnifying lens to see. Although rare in the wild, sweet coneflower is planted in gardens.

Wild golden glow (Rudbeckia laciniata), another look-alike, grows 5-10 feet tall in moist thickets, woodland edges, swamps and floodplains (2). Unlike brown-eyed Susan, its flower heads are 2-3 inches across. Its leaves are much larger – up to 10 inches long with three to seven deep lobes. For that reason, wild golden glow is also called cut-leaf coneflower.

Below are photographs of brown-eyed Susan and two of its look-alikes, black-eyed Susan and orange coneflower.

Brown-eyed Susan, Rudbeckia triloba. Stems are widely branched, reddish-green, and bristly. Flower heads are 1-2 inches wide. Bracts are hairy-bristly, tapered, and of unequal length. Lower leaves are three-lobed and coarsely toothed (2). 

Black-eyed Susan, Rudbeckia hirta. Plants are up to 3 feet tall with few branches. Flower heads are 2-3 inches wide with numerous, densely hairy, tapered bracts. Stems are green and densely hairy (hirta is from the Latin prefix hirt, meaning hairy or rough). Leaves are densely hairy on both surfaces, lance-elliptic, and with edges that are smooth or finely toothed.

Orange Coneflower, Rudbeckia fulgida, is native to the eastern U.S. but not Minnesota (5). It is common in gardens. Plants are up to 3 feet tall and somewhat branched. Flower heads are 2-3 inches wide with bracts that are more sparsely hairy than either Brown-eyed or Black-eyed Susan. Stems are green and bristly-hairy. Largest leaves are coarsely toothed but not lobed. Cultivars of Orange Coneflower may have slightly different characteristics. 

References

(1) Minnesota Department of Natural Resources, Division of Ecological and Water Resources. 2018. Rare Species Guide: an online encyclopedia of Minnesota's rare native plants and animals [web application]. Minnesota Department of Natural Resources, St. Paul. www.dnr.state.mn.us/rsg. Accessed August 19, 2021.

(2) Minnesota Wildflowers. Webpages for Rudbeckia triloba, R. hirta, R. laciniata, and R. subtomentosa accessed August 19-21, 2021, at  https://www.minnesotawildflowers.info/.

(3) Brown-eyed Susan, Rudbeckia triloba. Wisconsin Horticulture, Division of Extension, University of Wisconsin-Madison. Website accessed August 19, 2021, at https://hort.extension.wisc.edu/articles/brown-eyed-susan-rudbeckia-triloba/. 

(4) Tallgrass Prairie Wildflowers: A Field Guide. 1995. Text by Douglas Ladd, Photos by Frank Oberle. Published by Falcon Publishing, Inc., in cooperation with The Nature Conservancy.

(5) USDA, NRCS. 2021. The PLANTS Database (http://plants.usda.gov, 08/21/2021). National Plant Data Team, Greensboro, NC USA. [Web page for Rudbeckia fulgida accessed 8/21/21 at https://plants.usda.gov/home/plantProfile?symbol=RUFU2.]

Exotic Honeysuckles Change Feather Color

The finding underscores the unpredictability of invasive plant impacts.

Tatarian Honeysuckle (Lonicera tatarica) in early July. The fruits remain on the plant into August.

Most introduced plants – species imported from their natural ranges – are not harmful. The introductions that damage the environment, the economy or human health are called invasive, and their stories are much alike.

Arriving by accident or on purpose and without predators or pathogens to check their spread, invasive plants escape and eventually dominate areas outside cultivation, outcompeting native plants for water, nutrients and light. Some of them change soil chemistry or host other invasive species, further altering the communities they invade.

To a large extent, that’s the story of exotic bush honeysuckles. Four species are present in Minnesota and neighboring states: Tatarian Honeysuckle (Lonicera tatarica), Morrow’s Honeysuckle (L. morrowii), Bell’s Honeysuckle (L. x bella) and Amur Honeysuckle (L. maackii). All were introduced in the 1700s or 1800s as ornamentals, for erosion control or for wildlife habitat, and all are now recognized as invasive.  Once they are established, they displace native plants with their extended growing season, large, fast growth and prolific fruit production, which is their primary means of natural spread (1, 2). Together, their effect on native plant communities is considered second only to common buckthorn (2).

That’s sobering enough, but there’s another concern. Decades of observations have found that some birds are affected both indirectly by alteration of their habitats and directly by alteration of their appearance. Specifically, the berries of some exotic honeysuckles can change the color of their feathers, turning yellow parts orange and orange parts red.

Looking Back

The first reports of reddened feathers, called plumage erythrism, are from the early 1960s, when bird banders at Powdermill Nature Reserve in southwest Pennsylvania found Cedar Waxwings with orange tail bands instead of the normal yellow (3, 7). More observations followed, involving more species. White-throated Sparrows turned up with orange, not yellow, lores, the area between the base of the bill and the eye (4). Yellow-shafted Flickers, an eastern subspecies of Northern Flicker, were found with orange to red, not yellow, coloration on the undersides of their flight feathers (5). And since the early 1990s, male Baltimore orioles have been observed with red instead of orange feathers, particularly in the northeast U.S. and southeast Canada (6, 7).   

Left: An adult Cedar Waxwing, Bombycilla cedrorum. Photo by Ken Thomas via Wikimedia Commons. Notice the yellow tail band. Right: Tail band of a Cedar Waxwing showing normal yellow and abnormal orange color caused by deposition of rhodoxanthin. Photo courtesy Powdermill Nature Reserve, Carnegie Museum of Natural History.  

It took decades to find the cause. In the late 1980s, Jocelyn Hudon and Alan Brush, then with the University of Connecticut, analyzed the pigments in the yellow and orange tail bands of cedar waxwings. Along with several other pigments, they found rhodoxanthin, a red pigment then known primarily from the berries of yew (Taxus) and the leaves of some gymnosperms (Arborvitae, for example; (8).

Rhodoxanthin is different from the pigment that adds a splash of red to the birds’ wing tips. Because cedar waxwings can’t produce rhodoxanthin from other pigments they ingest, Hudon and Brush suspected it was introduced directly from the birds’ diet. In addition, because most of the birds with orange tail bands were juveniles, they suggested that the pigment came from something the nestlings were fed by their parents in July and August, when they were growing tail feathers. Whatever the food source was, they thought it was seasonally available, and because erythrism was recent – it was not documented in birds before the 1950s and 60s – the dietary source also had to be recent. They speculated:

If a dietary change is involved, the sudden appearance [of aberrant feather colors] might reflect the appearance of a new food source, a change in the abundance of a native or established source, or a change in adult food choice. (8)

Suspicions Confirmed

Speculation that change in feather color was caused by a change in food source was correct. Around the same time color aberrations were more widely observed, exotic bush honeysuckles were increasing in abundance. They and their cultivars were widely promoted and planted, and they found available habitat not just in landscapes and wildlife plantings but also in grasslands, brushlands and open woods, where they escaped. Feeding experiments and observations of wild birds confirmed that the source of rhodoxanthin was honeysuckle berries, especially those of Tatarian and Morrow’s Honeysuckle. Furthermore, plumage erythrism was found to affect not only nestlings but also adults that ate the berries during their summer molt. Rhodoxanthin consumed as they replaced their feathers was deposited like yellow or orange pigments, reddening the color of the tail bands (9, 10).

As exotic honeysuckles have spread, so have instances of plumage erythrism. Birders in the Midwest, including Minnesota and Wisconsin, have reported erythrism in cedar waxwings, white-throated sparrows and yellow-shafted flickers. Reports also come from Idaho, Montana, Utah and Alberta, Canada (10).

White-throated Sparrows (Zonotrichia albicollis) with normal yellow lores (left)

and abnormal orange lores (right). Photo courtesy Powdermill Nature Reserve,

Carnegie Museum of Natural History.

The consequences of changed feather color aren’t yet fully understood, but some ornithologists wonder if plumage erythrism could affect reproductive success (7, 10). Intensity of feather color is a measure of fitness. If males retain their reddened feathers into the breeding season, females may choose them over males that acquire their color “honestly,” that is, from activity and genetic advantage that signal better fitness. The result may be selection of breeding partners that are less able to produce and raise healthy offspring.

How to Help

The effect of exotic honeysuckle berries on feather color also points to the unexpected outcome of some plant introductions. Although not all introduced plants become invasive, those that do may have surprising – and still unknown – impacts on ecosystems, economies and health.

Fortunately, many landscape alternatives are available to anyone wanting to avoid the negative effects of invasive plants. Here are several sources of information.

• To learn which plants are invasive, start with this Minnesota DNR web page or see the Invasive Species tab above.
• To learn how to identify exotic honeysuckles, see this guide from MnDOT. More resources specific to introduced honeysuckles are listed on this Minnesota DNR web page.
• If you decide to replace non-native plants with native ones, you may be encouraged to know that an effective planting can be any size. To learn how one ecologist and gardener converted her backyard into a diverse, pleasing habitat, read Home Is Where the Habitat Is from the Minnesota Conservation Volunteer.
• If you’re looking for alternatives to invasive plants, there are many helpful resources. For trees, shrubs and woody vines, try the Landscapes Alternatives web page from the Woody Invasives of the Great Lakes Collaborative (WIGL). A free, downloadable brochure and a mobile app are available under the Landscape Alternatives pull-down menu.
• Another resource is Landscape Alternatives for Invasive Plants of the Midwest, a brochure that can be downloaded at no cost from the Midwest Invasive Plant Network.
• For lists of native plant suppliers and services, see the links under More to Explore, above right.

Finally, if you’re a birder, report any observations of birds with abnormally reddened feathers. This will help researchers learn more about the extent of plumage erythrism and its possible impacts. State ornithological societies and eBird may be appropriate places to submit reports. 

References

1. Woody Invasives of the Great Lakes Collaborative. Species accounts for Amur Honeysuckle, Morrow’s Honeysuckle and Tatarian Honeysuckle accessed July 27, 2021. https://woodyinvasives.org/
2. Smith, W R. (2008). Trees and Shrubs of Minnesota. University of Minnesota Press, Minneapolis.
3. All About Birds: Cedar Waxwing, accessed July 23, 2021. https://www.allaboutbirds.org/guide/Cedar_Waxwing/overview.
4. Powdermill Nature Reserve Avian Research Center, Carnegie Museum of Natural History. 2014 Late Fall bird banding report, https://powdermillarc.org/pictorial-highlights/late-fall-2014/. Accessed July 23, 2021.
5. Hudon, J., Driver, R.J., Rice, N.H., Lloyd-Evans, T.L., Craves, J.A., and Shustack, D.P. (2016). Diet explains red flight feathers in Yellow-shafted Flickers in eastern North America. The Auk 134(1): 22-33. 
6. Hudon, J., Derbyshire, D. Leckie, S., and Flinn, T. (2013). Diet-induced plumage erythrism in Baltimore Orioles as a result of the spread of introduced shrubs. The Wilson Journal of Ornithology 125(1): 88-96.  https://www.jstor.org/stable/41932838
7. Flinn, T., Hudon, J., and Derbyshire, D. (2007). The Tricks Exotic Shrubs Do: When Baltimore Orioles Stop Being Orange. Birding magazine, September/October 2007.  https://www.aba.org/birding_archive_files/v39n5p62.pdf
8. Hudon, J., and Brush, A. (1989). Probable dietary basis of a color variant of the Cedar Waxwing. J. Field Ornithol. 60(3): 561-568.
9. Witmer, M.C. (1996). Consequences of an alien shrub on the plumage coloration and ecology of Cedar Waxwings. The Auk 113(4): 735-743.
10. Hudon, J. and Mulvihill, R. (2018). Diet-induced plumage erythrism as a result of the spread of alien shrubs in North America. North American Bird Bander 42:95-103.

Some Uncommon Things About Common Milkweed

Common Milkweed, Asclepias syriaca, blooming on June 30, 2021, at Crow Hassan Park Reserve in Minnesota.

 

At times reviled as a nuisance of farm fields and pastures, Common Milkweed (Asclepias syriaca) has gained new respect as a plant that supports Monarch Butterfly larvae. That’s just part of the story, though. Here are a few things about milkweed that get less attention.

• The plant’s scientific name, Asclepias syriaca, is centuries old. It was given by Carl Linneaus, the Swedish botanist who in the 1700s developed the binomial system of nomenclature. That's the system that gives plants and other living things two names: a generic name – Asclepias, in this case – and a specific name, also called a specific epithet –syriaca for Common Milkweed.

• Linneaus is said to have been so impressed by the many medicinal uses of common milkweed that he named the plant after Asklepios, the Greek god of medicine. The specific epithet, syriaca, is from Linneaus’ mistaken belief that the plant came from Syria.  

• Syria is a long way from where common milkweed is naturally found. The plant is native to the Eastern and Great Plains regions of the U.S. and adjacent provinces of Canada. Like many plants, however, common milkweed has found its way overseas. It is now also found in southern and central Europe, where it invades grasslands and farm fields (1).

• One reason the plant isn’t always welcome is because it’s toxic to many animals, including humans. Like other milkweeds, the plant’s white latex contains cardiac glycosides, compounds that affect the function of the heart. Depending on the amount consumed, milkweed latex can cause symptoms ranging from nausea and vomiting to slowed heart rate, coma and even death (2).

• Some animals can eat milkweed safely. Milkweed bugs, for example, can isolate the cardiac glycosides they consume while they munch on leaves and other plant parts. The insects themselves then become toxic, which makes them unpalatable to predators. Their bright colors warn potential diners that eating them would be a mistake (3).

• Evidently, milkweed bugs have a lot of company. According to the U.S. Forest Service, common milkweed is a “mega food market” that feeds more than 450 kinds of insects. Some, like milkweed bugs, are destructive, but others merely sip the plant’s nectar or suck out its sap (4).

• Medicinal uses of common milkweed have waned, but not long ago, the plant saved lives in a different way. During World War II, milkweed pods were collected for the silks attached to their seeds. The buoyant, waterproof strands, called milkweed floss, were used to stuff life preservers when kapok, another plant fiber used for that purpose, could not be obtained from Indonesia.

• Milkweed floss was in such demand that school children were paid to gather the pods. The going rate was15 to 20 cents per onion bag or gunny sack filled with pods. Two bags provided enough floss to make one life preserver.

• Although it’s hard to imagine milkweed floss making much difference in the effort, the plant was abundant enough to have made an estimated 1.2 million life preservers. Milkweed was so valuable that the U.S. government considered it a “wartime strategic material” (5).

• After the war, common milkweed lost its status and was once again considered a weed. From reviled to revered and back again, shifting fortunes seem to define milkweed’s history.

References

(1) Asclepias syriaca (common milkweed). CABI Invasive Species Compendium. Viewed 6/30/21 at https://www.cabi.org/isc/datasheet/7249.

(2) Milkweed Plant Can Cause Serious Poisoning. Poison Control, National Capital Poison Center. Viewed on 6/30/2021 at https://www.poison.org/articles/milkweed-can-cause-serious-poisoning-204.

(3) Common Milkweed Insects. Susan Mahr, University of Wisconsin-Madison. Wisconsin Horticulture, Division of Extension. Viewed on 6/30/21 at https://hort.extension.wisc.edu/articles/common-milkweed-insects/.

(4) Plant of the week: Common milkweed (Asclepias syriaca).  David Taylor. U.S. Forest Service, USDA. Viewed on 6/30/2021 at Common Milkweed (fs.fed.us).

(5) A weed goes to war, and Michigan provides the ammunition. Gerald Wykes, from Michigan History magazine. Posted February 4, 2014, and updated January 20, 2019, on MLive. Viewed on 6/30/2021 at https://www.mlive.com/news/2014/02/a_weed_goes_to_war_and_michiga.html. 

Antsy Plants

From left: Wild Ginger, Nodding Trillium, and Bloodroot in early spring. 

Wild Ginger, Trillium and Bloodroot are done flowering, but that's not the end of their efforts. Now they must disseminate their seeds, and each has arrived at the same, six-legged solution to accomplish that task: Ants.

Myrmecochory (often pronounced MUR-mecco cor-ee), the dispersal of seeds by ants, is a convenient invention. Ants are found all over the world, from the tropics to the Arctic, so they are a ready resource. Similarly, plants that employ ants for seed dispersal live in diverse habitats, including the tropical rainforests of Latin America, the dry shrub communities of South Africa and Australia, and the eastern deciduous forests of Europe and the U.S. (1). Myrmecochory is thought to have developed independently more than 100 times, with more than 11,000 species of plants relying on these insects to spread their seeds (2).

That nature converged on the same solution in different, and distant, plants suggests that it works. Like any method of seed dispersal, though, myrmecochory has a cost. It demands adaptations, and in one group of ant-dispersed plants, that adaptation is in the form of a bribe.

To lure ants, myrmecochores attach small, fatty bodies called elaiosomes (e-lay-o-somes) to their seeds or fruits. Depending on the species, these mini nutritional packets are clear, white, brown, or other colors and shaped like worms, flags or amorphous dollops. Some may emit an odor like rotting insect carcasses, a trick to attract ants to take the seeds back to their nest, remove and feed the elaiosomes to the colony, and leave the seeds to germinate (1).

From left: Wild Ginger, Nodding Trillium, and Bloodroot seeds with their elaiosomes.

Both plants and ants are thought to benefit from this relationship. Plants benefit by reducing competition for light and nutrients between parent plants and their offspring. Moving seeds away from the parent plant also lessens the risk of local extinction: If one part of a population dies, another, more distant, part may survive. Another potential benefit is reduced seed predation. Perhaps better than any other animal, ants can disperse a cache of seeds meters away from the parent before mice, birds or other seed eaters find them.

One more potential benefit is improved seed germination. Seeds discarded in or near ant nests may end up in refuse piles, nutrient-rich microenvironments that can aid germination and seedling growth. The medium in ant nests may also retain more water or be better aerated, another potential aid to germination and growth. 

Ants benefit from myrmecochory, too, and it's likely they're adapted to the interaction. Not all species of ants forage for seeds that have elaiosomes, but those that do may have some yet-unknown characteristics that lead them to that behavior. Widespread though it is, this mutually beneficial relationship still has some secrets to share.

Myrmecochores of Minnesota

The ant-dispersed plants in this region tend to be early-blooming herbs of deciduous forests. Here are a few, based on personal observation or mention in references. 

Bloodroot (Sanguinaria canadensis)

Nodding Trillium (Trillium cernuum)

Wild Ginger (Asarum canadense)

Yellow Violet (Viola pubescens)

Spring Beauty (Claytonia virginica)

White Trout Lily (Erythronium albidum)

References

(1)    Handel, S.N., and Beattie, A.J. (1990). Seed dispersal by ants. Scientific American 263 (2): 76-83B.

(2)    Lengyel, S., Gove, A.D., Latimer, A. M., et al. (2010). Convergent evolution of seed dispersal by ants, and phylogeny and biogeography in flowering plants: A global survey. Perspectives in Plant Ecology, Evolution and Systematics 12: 43-55.

Plant Profile: Wild Geranium

Wild geranium (Geranium maculatum) is a native, herbaceous perennial of open woods and woodland edges. It begins blooming in May, about the same time as Trillium, with loose clusters of pink to lavender flowers at the ends of hairy stems. The plant is also called wild cranesbill or storksbill for the long, beak-like capsules produced after flowering.

In the flower on the left, the inner ring of anthers is releasing pollen.

The stigma is not yet mature. On the right, the anthers are past maturity

and the curled, five-parted stigma accepts pollen.

The anthers in a flower mature first – an outer ring and then an inner ring – followed by the stigma of the pistil, a sequence that favors cross-pollination (1). A variety of bees, flies and beetles visit the flowers for nectar and pollen, guided, or maybe lured, by the lines on the flowers’ petals. Larvae of several insects also feed on the plant (1).

Collecting seeds from wild geranium can be tricky. As a capsule matures and dries, each of its five parts separates from the central column and curls upward, flinging the seed from the oval chamber at the base. To catch the seeds, it's best to collect the capsules when they just begins to change color. Put them in a closed paper bag to dry and release its seeds. 

The seeds need a period of cold, moist conditions before they will germinate, so either sow them outdoors in fall or treat them artificially (2). Instructions are available from Prairie Moon Nursery, prairiemoon.com.

Left: A nymph of the Fork-tailed Bush Katydid (Scuddaria furcata) visits a Wild Geranium flower. Right: A Thick-headed Fly (Myopa species) sips nectar.

Wild geranium also reproduces vegetatively. Thick rhizomes produce patches of plants that can be divided, ideally in spring or fall. Cut the rhizomes where they make right angles (2). Of course, don’t harvest rhizomes on public land or on private land without permission.

Immature (left) and post-mature (right) capsules of Wild 

Geranium. Seeds have already been released from the 

capsules on the right.

A few plants have leaves that look like wild geranium. Sanicles, also called black snakeroots (Sanicula species), grow in a similar habitat but have alternate leaves on the stem, in contrast to the opposite leaves  of wild geranium. Also unlike wild geranium, Sanicle stems and leaves have no hairs (5). Canada anemone (Anemone canadensis), usually found in wetter habitats than wild geranium, has leaves with sharper teeth (3). Like wild geranium, its stems are hairy, but the hairs are spreading or ascending. In contrast, the hairs on the stems of wild geranium point downward (5)

 

Wild Geranium spreads vegetatively by rhizomes. The largest

one is about as thick as a thumb.

References

(1)    Pollinators of Native Plants, by Heather Holm. Pollination Press, Minnetonka, MN. 2014.

(2)    Wild Geranium, Geranium maculatum. Wisconsin Horticulture, Division of Extension. University of Wisconsin-Madison. Website accessed May 31, 2021. https://hort.extension.wisc.edu/articles/wild-geranium-geranium-maculatum/

(3)    Geranium maculatum (Wild Geranium). Minnesota Wildflowers. Website accessed May 31, 2021. https://www.minnesotawildflowers.info/flower/wild-geranium

(4)    USDA, NRCS. 2021. The PLANTS Database (http://plants.sc.egov.usda.gov, 05/28/2021). National Plant Data Team, Greensboro, NC USA.

(5)    Flora of the Great Plains, by the Great Plains Flora Association. University Press of Kansas, Lawrence. 1986.