Incised Fumewort: A Fast-Spreading Invasive Plant to Watch For in the Mid-Atlantic

Incised fumewort (Corydalis incisa) is an annual or biennial herb native to East Asia. First found in the United States in Bronx County, New York, in 2005, it has since spread quickly through Pennsylvania, D.C., Virginia, Maryland and North Carolina, with iNaturalist records as far west as Illinois and Tennessee. This guide comes from Sara Tangren of the NatCap PRISM invasive species partnership at the Metropolitan Washington Council of Governments and Yvonne Ng of the National Park Service.

Invasive incised fumewort. Photo: KENPEI, CC BY-SA 3.0, via Wikimedia Commons.

How fast it's spreading

In 2017 the U.S. Department of Agriculture rated it a "high risk" invader, likely both to spread widely and to do real damage. The USDA's assessment noted that it:

• tolerates shade;
• can fertilize itself and produces lots of seed;
• flings its seeds up to three meters from bursting capsules, after which ants or water can carry them farther;
• appears to be spreading as a contaminant in nursery stock;
• forms dense patches and, at some stages, shrugs off hand-pulling and clipping.

How to identify it

It grows up to 2 feet tall. In the National Capital Region, the authors have observed this yearly cycle:

The leaves are compound: split into three leaflets, each split again into three lobed or toothed parts. Look for it along waterways, on rock walls, in disturbed ground, and in moist and floodplain habitats.

Don't confuse it with the native

The native yellow corydalis (Corydalis flavula) grows along riverbanks, rock outcrops and slopes. The two are easiest to tell apart in flower:

The winter leaf differences are real but gradual and inconsistent from plant to plant, fade by spring, and are hard to use unless the plants are side by side.

Reporting a sighting

Good records help track the invasion. Photograph:

• the surrounding landscape, to show context and the size of the infestation;
• a whole plant with flowers and leaves, if it's blooming;
• a whole, typical, undamaged leaf, if it isn't.

Note: whether the plant looks deliberately planted, weedy or escaped; a rough count of patches or the area covered; and anything else that might help.

Sources

Based on "Incised Fumewort (Corydalis incisa)," by Sara Tangren, NatCap PRISM, Metropolitan Washington Council of Governments, and Yvonne Ng, National Park Service, published by the National Park Service; rewritten in hubnx's own words.