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. 

The Pretty Problem of Siberian Squill

Siberian Squill (Scilla siberica) is an introduced plant that blooms in early spring. Leaves are basal, up to six inches long and 1/2 inch wide. Flowers are blue on leafless stalks. This ephemeral plant dies back in late spring. 

Siberian squill is a beautiful, eye-catching plant. Its bright blue flowers are among the first to bloom in spring, providing a pop of early color in gardens, lawns and woodlands. To many who are winter-weary, it's a welcome sight.

Lately, though, the plant is getting attention for a different reason. The same qualities that have long made Ssquill popular – its profusion of flowers, its tendency to spread into masses, its easy propagation – have also raised suspicions that it can be invasive. In some places, squill has jumped the garden border or the naturalized planting to grow where it wasn’t intended. That includes deciduous forests, where there is rising concern that it can displace native woodland plants.

It has taken a long time, and some long-distance travel, to get here. Squill is thought to have arrived in the United States in the late 1700s, when it was imported from its native range in southwest Russia and the Caucuses [1].  Promoted as an ornamental, it reached the Midwest by the mid-1900s. The first record of squill in the Wisconsin State Herbarium [2] is a plant collected in 1955 from Hortonville, in eastern Wisconsin. Later herbarium records find it at Point Beach State Forest near Manitowoc in 1964, the campus of UW-Oshkosh in 1966, and Turville Woods, west of Milwaukee, in 1975.

Squill reached Minnesota sometime later. The garden census for the Eloise Butler Wildflower Garden has counted squill among its numbers since 1985 [3]. The earliest herbarium records from the Minnesota Biodiversity Atlas [4] are dated 1997, when squill was found in Forestville State Park, and 1999, when it was found in Frontenac State Park, both in southeast Minnesota. Today squill is found throughout much of the state.

Judging from records of its distribution, squill can live quite well outside tended plantings. Freed of any apparent constraints, it can reproduce quickly by bulbs and seeds to form potentially large populations. A sample of EDDMapS reports [5] gives some idea of its ability to spread: 7 square feet of cover in a Rochester park; 800 square feet in a park in Maple Grove; an acre – about 43,000 square feet – in the Roberts Bird Sanctuary in Minneapolis, where squill escaped from a garden into an adjacent woodland reserve.

According to these reports, not all wild populations are (yet) large and dense, but there are more clues this can happen. In fact, some people want it to happen. For example, many gardening websites and advertisements picture broad expanses of squill, wide carpets of blue below an overstory of handsome trees. Far from being a red flag, squill’s habit of spreading is viewed as positive. If the pictures don't say it, the words that accompany them do: “Great naturalizer,” proclaims one advertisement. “Best when planted in large drifts,” advises another. One more takes that advice a step further: “Mass in sweeping drifts in woodland, wild or naturalized areas.”

The fear, again, is that sweeping drifts of squill could broom other plants out of existence. Several native spring wildflowers – bloodroot, wild ginger, Trillium, Hepatica, spring beauty, and others – share a similar woodland habitat and phenology, and they may be unable to compete with an aggressive introduction like squill. Proof of harm needs formal research, but until any such studies are complete, informal studies, reports, and observations are raising concerns.

Suspicions are now great enough that leaders in the gardening world are urging caution. The University of Minnesota Extension Service [6] warns that although squill is beautiful, it may be harmful. “Because of its rapid spread and condition tolerance,” they write, “this non-native species has the potential to become an invasive plant.”

At the Minnesota Landscape Arboretum, managing squill has become a struggle. Gardeners there are frustrated by the difficulty of establishing other plants where squill has spread. One gardener tried digging out squill and planting wild ginger. Unfortunately, two years later squill had rebounded and the wild ginger was all but gone [9].

The Southeast Wisconsin Invasive Species Consortium [7] is also wary. Calling squill “a classic case of gardening gone awry,” the group is alert to the probability of trouble. Citing the plant’s cold hardiness and unpalatability to deer and other herbivores, they lament the consequences of its popularity: “Sadly, the same traits that make it attractive as a garden plant . . . are also what make it invasive.”

 

Understandably, fans of squill find this hard to accept. A lively debate on the Minnesota Wildflowers website includes defenders who like the plant for its beauty, its role as a harbinger of spring, and its sentimental value. Some assert that the plant is well-behaved and is a food source for pollinators. Others want proof that squill displaces native plants.

 

The debate goes to the heart of invasive species biology. Many plants are introduced because, like squill, they're beautiful. People plant them because they admire them. Most of these species cause no harm to natural areas. Marigolds, petunias and impatiens, for example, usually stay put. A few introduced species, though, have it in them to spread. They might limp along for a while, but eventually they gain enough of a toe hold to dominate a landscape, whether it’s a garden, a yard or a natural area. 

Increasingly, squill appears to be one of those runaway species. Some gardeners and natural area stewards have spent years trying to remove squill from garden plots, lawns and woodlands, and their frustration is clear. So are their warnings. They advise removing squill when its populations are small and easier to take out. Better yet, they say, avoid the problem by not planting it at all. 

Proof of harm to native plants and pollinators will take time to complete. If studies confirm that squill is invasive, it will be years before that evidence is published. In the meantime, it's clear from a growing number of observations that squill as an emerging concern. As one gardener at the Arboretum put it, “It’s beautiful, but it’s very invasive. When it naturalizes too much, it’s difficult to get rid of.” [8]

 

Squill is indeed beautiful. This unique plant reminds us of spring and perhaps of those who planted the bulbs with good intentions of creating a pleasing landscape. However, if we’re on the cusp of recognizing that squill can be harmful, now is the time to act. In some places, at least, this pretty plant has become a big problem.

 

Squill Removal and Look-Alikes

Removing Squill can be a tough job, especially if it’s growing in masses. For tips, scroll through the discussion on Minnesota Wildflowers and see the advice from the University of Minnesota Extension Service [6].

 

Squill is easiest to recognize when it’s flowering, but it has some look-alikes.

 

Harebell (Campanula rotundifolia) has bell-shaped, purple flowers on leafy stems reaching 20 inches tall. Typically, it grows in dry, open places. It blooms in summer.

 

Blue-eyed Grass (Sisyrinchium species) has grass-like leaves and dark to pale purple flowers with yellow centers and yellow anthers. Squill has blue anthers. Three species grow in Minnesota, all in sun. They bloom from May to July.

 

Like Squill, Spring Beauty (Claytonia virginica) is a woodland spring ephemeral. It blooms a little later than Squill and has pink-veined flowers. Flowering stems bear long, narrow leaves.

From left: Spring Beauty, Harebell, and Mountain Blue-eyed Grass, Sisyrinchium montanum.
Harebell photo copyright 2008 Katy Chayka. Blue-eyed Grass photo copyright 2012 Peter Dzuik. Both photos are from Minnesota Wildflowers.

 

 

References

[1] Flora of North America. Scilla siberica. Website accessed May 2021.

 

[2] Consortium of Midwest Herbaria, midwestherbaria.org. Accessed May 2021.

 

[3] The Friends of the Eloise Butler Wildflower Garden. Blue Squill, by G.D. Bebeau. 2015. Accessed May 2021.

 

[4] Minnesota Biodiversity Atlas. University of Minnesota Bell Museum. Accessed May 2021.

 

[5] EDDMapS. 2021. Early Detection & Distribution Mapping System. The University of Georgia - Center for Invasive Species and Ecosystem Health. Available online at http://www.eddmaps.org; last accessed May 7, 2021.

 

[6] University of Minnesota Extension Service. Squill, by Angela Gupta, Amy Rager and Megan Weber. Reviewed 2021.

 

[7] Southeastern Wisconsin Invasive Species Consortium, Inc. (SEWISC).  Siberian Squill. Website accessed May 2021.

 

[8] Pretty, but aggressive squill, by Erin Buchholz. Nature Notes. News from the Minnesota Landscape Arboretum. May 13, 2020.

 

 

 

 

Bloodroot's Bet

This herbaceous perennial is among the first to bloom on the deciduous forest floor. It's also among the hardiest.

Bloodroot, Sanguinaria canadensis, in early April 2021.

Every year, bloodroot throws the dice. It blooms surprisingly early, risking the return of winter weather to grow and flower when light intensity is highest on the deciduous forest floor. Its way of surviving in shade is to mostly avoid it, and thanks to several adaptations to cope with the uncertain conditions of early spring, it has succeeded.

Sometime in late March or early April, single basal leaves spear through the leaf litter, wrapped around and protecting flower stalks bearing one, delicate bud. On dry, sunny days, the flowers open like bowls, each a brilliant display of eight or more petals around a mass of orange-yellow stamens and a central pistil.

Little else is blooming at the time, so bloodroot doesn’t have much competition for the few pollinators that are active in early spring. Although bloodroot has no nectar, insects nevertheless circle over the flowers in search of a sugary sip.  A few will land inside, and over the course of a few days, they will find that Bloodroot’s offerings change.

When a flower first opens, only the stigma is mature. The anthers need another day or two before they’re ready to release any significant amount of pollen. Although visiting insects won’t find much pollen to gather from a young flower, they can deliver what they collected from an older one. In rapid succession, the stigma receives the pollen, the eggs are fertilized, and seeds begin to develop. Such cross-pollination has the advantage of mixing genes from different plants, creating new combinations that might improve offspring survival.

Self-pollination isn’t likely to occur at this stage, in part because the anthers aren’t mature but also because the stamens initially bend away from the pistil. By day three in a flower’s life, however, the anthers are fully developed and the stamens change their position. Instead of bending away from the pistil, they bend toward it, increasing the odds that the flower will fertilize itself.

Left: In recently-opened flowers, the stamens and immature anthers bend away from the pistil.
Right: In an older flower (three days or so), the stamens bend toward and even arch over the pistil.

In a sense, this is bloodroot’s life insurance policy. If cross-pollination doesn’t happen – say in a stretch of cold, rainy or snowy weather that limits pollinator activity – self-pollination is a fallback. The resulting seeds will produce offspring much like the parent, but at least there will be seeds, tiny propagules that can be disseminated to expand the population.

Whatever ate these Bloodroot leaves might not have
enjoyed them for long. Bloodroot sap contains several
alkaloids, bitter molecules that can be harmful.

Of course, insects aren’t the only animals looking for food in early spring. Hungry herbivores are also on the prowl, and bloodroot provides some tempting, tender shoots. One chomp and bloodroot could lose its annual opportunity to grow and reproduce. The “blood” of bloodroot tends to discourage that activity, however. It contains several alkaloids, molecules that are distasteful if not harmful to animals that eat them. Alkaloids are most concentrated in the roots, but they are found in all parts of the plant, including the leaves and petioles. A mouthful of the bitter greens could be enough to put an herbivore off bloodroot for a long time.

It’s a gamble to grow early, but bloodroot has adapted to the risk. The plant's fragile appearance belies a durability born of countless generations on the forest floor. Through genetic trial and error, the dice came to be loaded in its favor.     

References

Hayden, W.J. (2005). Bloodroot pollination: Bet-hedging in uncertain times. Bulletin of the Virginia Native Plant Society 24(1): 5+

Matsuura, H., & Fett-Neto, A. (2015). Plant Alkaloids: Main Features, Toxicity, and Mechanisms of Action.

Schemske, D.W., Willlson, M.F., Melampy, M.N. et al. (1978). Flowering ecology of some spring woodland herbs. Ecology 59 (2): 351-366.