Exploring the science of plants, from the field to the lab

Detecting an Invasive Plant Before It’s Too Late

Posted in Interesting Plant Stories on July 3, 2014 by Daniel Atha

Daniel Atha is a Research Associate at The New York Botanical Garden. Jessica Schuler is Director of the Botanical Garden’s Thain Family Forest. Sarah Lumban Tobing is a Project Manager for Forestry, Horticulture and Natural Resources at the New York City Department of Parks and Recreation.

Purple keman (Corydalis incisa)
Purple keman (Corydalis incisa)

The latest threat to our local environment comes from an Asian plant that resembles wild chervil when young and has the potential to out-compete native species.

A member of the fumitory family, Corydalis incisa, or purple keman, is native to China, Korea, and Japan. It was first discovered growing wild in North America during the 2005 Bronx Park BioBlitz, north of The New York Botanical Garden.

A rapid survey of the same area in May revealed populations on both sides of the Bronx River and extending throughout the annual floodplain, consisting of both first-year seedlings and second-year flowering and fruiting plants. Within one heavily infested area, 32 seedlings were counted in an area of 100 square centimeters (a little more than 15 square inches).

Also this year, we found a previously undocumented infestation, 7.5 miles northeast in the Bronx River Reservation of Westchester County, representing the second known population in North America and the first report of the species for Westchester County.  The sighting was immediately reported to Westchester County Parks Department and we are now working with Brenda Bates of the Conservation Division to document and monitor the plants.

Continuing the survey work here at the Botanical Garden, we found scattered individuals of mostly second-year plants around the Magnolia Way Bridge at the north end of the Garden. No plants were found further south in the Garden, perhaps because the banks are rocky and unsuitable for germination.

Purple keman thrives on fine, alluvial sediments, competing with native riparian understory plants including Virginia knotweed (Polygonum virginianum), white snakeroot (Ageratina altissima), jewelweed (Impatiens capensis), wood nettle (Laportea canadensis) and woody seedlings. The very aggressive lesser celandine (Ranunculs ficaria) and Japanese knotweed (Reynoutria japonica) were also present and abundant.

It is not known how the species became established in the wild, but given the plant’s limited range and its biological traits, we suspect that they were first cultivated in Westchester County near the Bronx River. The plants spread by seeds that are ejected when the plants’ fruits burst open, and in this case the seeds were likely dispersed downriver during floods.

When very young, purple keman plants resemble wild chervil (Anthriscus sylvestris), mugwort (Artemisia vulgaris), Canadian honewort (Cryptotaenia canadensis), and Clayton’s sweetroot (Osmorhiza claytonii), all of which may grow abundantly in the same habitat. The plants quickly flower, fruit, disperse their seeds and then die back, leaving no trace—except for the tiny seeds.

The Garden, the New York City Department of Parks and Recreation, the Bronx River Alliance, and the Westchester County Parks Department are working in collaboration with the Lower Hudson Partnership for Regional Invasive Species Management (Lower Hudson PRISM) to assess the extent of the invasion and determine how it should be monitored and managed in the future.

Forest staff weeded the plants in the Garden this year and will continue to monitor and manage the species in the future. New York City Parks staff members are making plans to hand-pull second-year plants before they fruit and disperse their seeds next year.

Through these efforts, all known populations of Corydalis incisa in North America have been documented with herbarium specimens that will be archived in the William and Lynda Steere Herbarium and be available online through the C. V. Starr Virtual Herbarium, providing a permanent record for current and future research and management.

Locations were entered into New York State’s interactive web-based invasive species mapping database called iMapInvasives. Led by the New York Natural Heritage Program, iMapInvasives is used for the collection, distribution, and analysis of invasive species observation, survey, assessment, and treatment data. The program enables managers to coordinate early detection and rapid response through e-mail alerts and provides data that can be used in GIS modeling.

If you would like to take action and become trained to use this interactive citizen science database, you are invited to a training session at the Garden on July 7, 2014. Register for this program here. Everyone is encouraged to participate in Invasive Species Awareness Week (July 6–12), a statewide initiative to promote knowledge and understanding of invasive species and to stop their spread by engaging citizens in a range of activities across the state.

This work on Corydalis incisa is just one example of how we can work together to promote conservation and stop the spread of invasive species.


Kris Thompson said:

I live in southeastern Nebraska and have about 50 square feet of unidentified low-growing Corydalis on a steep bank in dry shade.
It had already flowered and started producing seed heads before I noticed it.
Is there somewhere that I can post images of it to try to identify what species it is?
We already have our hands full battling Lonicera maackii, so if this is another invasive I’d like to get it before it spreads further.