King County weed specialists recently responded to a report of a new forest invader called small-flowered jewelweed found along Novelty Hill Rd just east of Redmond Ridge. This central Asian species is a widespread invasive plant in European forests, but is still highly localized in North America. According to a 2013 USDA-APHIS report, it is being reviewed for possible listing as a Federal noxious weed and was listed as a pest plant under “Not Authorized Pending Pest Risk Analysis (NAPPRA) regulations”.
Previously, small-flowered jewelweed was known to occur in only one other place in Washington State, a small patch near the Woodland Park Zoo in Seattle. Thanks to the tip from University of Washington botanist David Giblin, King County weed specialists were able to control this new patch on Novelty Hill Rd the same season it was discovered.
Scientifically known as Impatiens parviflora, small-flowered jewelweed is in the balsam or touch-me-not family. For photos and more information see the UW Burke Museum Herbarium website.
This new location in King County is a reason for concern. In 2013, a large population of small-flowered jewelweed was found in Portland, Oregon by Peter Zika and it is also known to occur in British Columbia, so it is likely that this species is in more places than we realize in our state. The Washington State Noxious Weed Board is asking for everyone to keep an eye out for this plant throughout the state. See their Facebook post for more information.
The good news is that this finding is an excellent example of successful early detection and rapid response. The patch was first discovered earlier this summer by botanist Alexander Wright and the species identification was confirmed by David Giblin, who then reported it to the King County and Washington State Noxious Weed Boards in late August. County employees Mattia Boscolo from the Noxious Weed Program and Garrett Zwar from the Roads Division met at the site the following week and controlled all the plants, preventing further spread. They will follow up later this fall and again next year to look for additional plants in the area.
Small-flowered jewelweed is a short, shade-tolerant herbaceous plant that prefers somewhat moist forests or forest edges. It looks like a stunted version of the noxious weed policeman’s helmet (Impatiens glandulifera) but with delicate, pale-yellow flowers instead of large pink flowers.
Interestingly, at the Novelty Hill site, the small-flowered jewelweed was growing with another species of Impatiens called spotted jewelweed (Impatiens capensis), also not native to Washington and fairly invasive as well, and may even have been out-competing the spotted jewelweed. Although similar looking, the two jewelweeds are fairly easy to tell apart. Spotted jewelweed flowers are larger and distinctly orange with reddish-brown spots, compared with the small, pale-yellow flowers of small-flowered jewelweed. The leaves are also shaped differently, with spotted jewelweed having more rounded, scalloped-edged leaves and small-flowered jewelweed having more pointed, saw tooth edged leaves.
WSU Extension researcher Tim Miller reported seeing small-flowered jewelweed in Prague this summer and said it looked very bad where he saw it. Indeed, according to information from CABI.org, Impatiens parviflora (called small balsam in Europe) is “one of few plants to successfully invade undisturbed forest vegetation”. Originally introduced intentionally in gardens as a botanical novelty, it is now widespread and well-established in much of Europe.
Like other touch-me-nots, small-flowered jewelweed spreads by seed, which are explosively ejected up to 10 feet away. Seed also float in fast-moving water and are helped further by being carried on animals and birds, footwear, vehicle tires, and with timber. In Central Europe, it is often found in managed forests and timber plantations as well as more natural, undisturbed forests.
If you notice small-flowered jewelweed growing in Washington, please report it to the Washington State Noxious Weed Control Board or your local county weed board. In King County, you can email us directly at firstname.lastname@example.org or use our online report-a-weed form. Help us stop this new invader before it gets out of hand!