Lesser-celandine-ranunculus-ficaria roots Photo from wikimedia.org

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In case you missed it, scatterings of pretty little yellow flowers amid lush green foliage have sprouted throughout Evanston over the past few weeks. Their sunny faces surprised gardeners, cheered up drab landscapes, and bridged the dreary transition from winter to spring.

But do not be fooled: those sweet sunshiny blooms are Public Enemy #1, a non-native invasive plant called Lesser Celandine, also known as Fig buttercup. Traveling far from its original home in Europe, Northern Africa, Western Asia, Caucasus, and Siberia, Lesser Celandine has landed on the 2016 “Most Unwanted Invasive Pests” list compiled by the Illinois Cooperative Agriculture Pest Survey Program. It keeps company with other nefarious invaders like Asian Longhorn Beetles, Sudden Oak Death, Spotted Lantern Flies, Boxwood Blight, and Giant Hogweed. What turns an innocent looking flower into a national nuisance?

“Lesser Celandine emerges in advance of the native flora, so it can quickly establish and form large dense patches that will outcompete our native species,” explains Nancy Kreith, a Horticulture Educator with the University of Illinois Extension in Matteson. Lesser Celandine’s aggressive early growth can suppress spring ephemerals – short-lived plants such as fringed bleeding heart, spring beauty, mayapple, wild ginger, trilliums, and Virginia bluebells. Spring ephemerals emerge and bloom before trees leaf out, providing nectar, pollen, fruit, and seeds for native insects and wildlife. Then they produce or “set” seeds and die back until the following spring.

“That diversity of spring ephemerals is really important for pollinators looking to forage early after a long hard winter,” Ms. Kreith says. Early and varying bloom times are key for early pollinators’ survival. When Lesser Celandine shades out early bloomers and blocks their growth, early pollinators miss out on their usual food sources, which can throw the ecosystem out of balance.

Distinguished by its kidney-shaped glossy green leaves and small yellow flowers with between 8 and 12 petals, Lesser Celandine (Ficaria verna) often is mistaken for marsh marigold and swamp buttercup, both of which are native plants. Marsh marigold (Caltha palustris) has rounder leaves similar to wild ginger, sports yellow flowers with between five and nine petals, and grows in clumps rather than spreading like ground cover. Swamp buttercup (Ranunculus septentrionalis) has groups of three leaves, five-petaled yellow flowers, and grows in bushy clumps.  

In folk or botanical medicine, Lesser Celandine goes by the name “pilewort,” referring to its use as an external remedy for hemorrhoids or “piles.” Studies have found that people who take Lesser Celandine internally risk acute liver toxicity. Not surprisingly, the Food and Drug Administration has not approved Lesser Celandine for medicinal use.

The National Park Service reports that Lesser Celandine thrives in open woods, floodplains, and meadows, preferring sandy soils and spreading via its tuberous roots and little cream-colored bulblets at the plant’s base. But whatever it “prefers,” Lesser Celandine seems to love Evanston lawns, gardens, and other open spaces, and undoubtedly local landscaping companies are getting the S.O.S. from their clients.

“I would say this year seems like we’re getting more phone calls about it,” says Steve Neumann, owner of Evanston-based Logic Lawn Care, which specializes in organic fertilization and natural weed control. While Lesser Celandine typically starts to bother homeowners at this time of year, Mr. Neumann assures that relief is on the way. “It’s literally going to disappear in a couple of weeks, and then it’s out of sight out of mind until next year,” he says.

Chicago Botanic Garden in Glencoe advises removing Lesser Celandine “as soon as possible, including all cultivars, and/or do not add to collection in the future.” They also suggest wild ginger (Asarum canadense) and twinleaf (Jeffersonia diphylla) as alternatives to plant in its place.

Gardeners and homeowners wanting to vanquish the unwanted intruder have several options, including manual removal and chemical control. Small patches can be dug out by hand before the plant dies back; Ms. Kreith advises pulling the whole root base and catching as many bulblets as possible. “If you leave any of those tuberous roots, it will come back,” she says. Place dug up plants in a plastic bag and dispose of them in the regular trash or an incinerator rather than a yard waste bin or compost heap, to keep them from taking hold somewhere else.

Larger patches might need an herbicide such as glyphosate, which Ms. Kreith says should be applied with a paint brush rather than spraying so it won’t kill nearby plants. Glyphosate, famously known as the main ingredient in Roundup, is a systemic herbicide that kills plants down to the roots. It is most effective when applied before the Lesser Celandine patch is about half in bloom, when the plant is vulnerable and still establishing itself. Ms. Kreith advises wearing protective gear and clothing, and reading the label carefully.

Mr. Neumann’s company prefers natural weed control, and is successfully treating Lesser Celandine and other unwanted plants with an iron-based organic herbicide.

“It’s not a one-time one-year solution, but it dramatically suppresses the plant so it has to start over as a smaller plant the next year,” he says. It can take two to three years to fully eradicate a patch of Lesser Celandine, but natural herbicides – also known as bioherbicides – are safer for the soil and for animals that might come into contact with it.  Home gardeners should be able to find weed control with chelated iron either at garden centers or online.

Because Lesser Celandine will be dying back soon, Mr. Neumann advises removing or killing off as much as possible now, then making a reminder to watch for it in the same locations early next spring. Take a few photos now to remember how it looks, and spray or dig it up as soon as it starts emerging in 2018. He reiterates that it will take several years to fully eradicate this particular invader.

The Urban Ecology Center in Milwaukee notes that Lesser Celandine has no natural local enemies – animals, birds, insects, bacteria, fungi, etc. – to keep it under control in our part of the world. Such organisms would eat or otherwise help control Lesser Celandine in its native habitat. Since May is Illinois Invasive Species Awareness Month, this is a good time to identify it in a lawn or garden and start getting rid of it.

The U.S. Department of Agriculture’s website invasivespeciesinfo.gov offers advice on how to prevent the spread of invasive species, provides a lengthy list of smartphone apps for monitoring them, and lists sources for reporting invasive species to state agencies.