Cardamine impatiens (Narrow-leaf Bittercress)
|Also known as:||Bushy Rockcress|
|Life cycle:||annual, biennial|
|Habitat:||part shade, shade; moist woods, thickets, stream banks|
|Bloom season:||May - July|
|Plant height:||6 to 30 inches|
|Wetland Indicator Status:||GP: none MW: FAC NCNE: FAC|
|MN county distribution (click map to enlarge):|
|National distribution (click map to enlarge):|
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Flowers are in rounded clusters averaging ½ inch across at the top of the plant and at the end of branching stems. Individual flowers are white to greenish, tiny with 4 petals but these are typically absent or indistinct.
Leaves and stem:
There are both basal and alternate stem leaves. Stem leaves are compound in groups of 13 or more, to 6 inches long. Leaflets are generally lance to arrowhead-shaped, about 1 inch long with asymetrical bases; the edges may be smooth, jagged or sharply toothed.
Basal leaves are compound in groups of 3 to 11, with rounded lobes that may be further notched or lobed, and asymetrical bases. Leaves and stems are hairless. Flowering stems are usually produced the second year.
Fruit is a straight slender pod, erect to spreading, up to about 1 inch long. Ripened pods burst open and can shoot seed several feet from the mother plant, thus it can form dense colonies fairly quickly and crowd out native plants.
Narrow-leaf Bittercress may resemble some other Cardamine species, most notably Pennsylvania Bittercress, but the latter has larger and better defined flowers while the former has the distinct auricles at the leaf base. This is a new exotic species in Minnesota, and highly invasive. According to the MN Dept. of Agriculture, a single plant was discovered at Riverside Park in 2008; by 2009 they were pulling out truckloads of it. So far it has been found mostly in the Mississippi River Valley, and probably spreads via the river. At Battle Creek Park in St. Paul, it has been found along the dirt bike trails throughout wooded areas. It is very likely that weed seed is transported by bikers and dog walkers when they travel from infested to uninfested areas without cleaning their bike tires, footwear, or animal's feet and coat. This is a continuing problem in the battle against invasive species—always clean your gear!
Narrow-leaf Bittercress is a targeted Early Detection species and needs to be stopped before it becomes more unmanageable. The root system is shallow and it hand pulls easily, but herbicide is recommended for larger infestations. See the MN Dept. of Agriculture's fact sheet for more information on control measures. If you have spotted this plant anywhere in MN, please post a comment below so new infestations can be dealt with as quickly as possible.
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Photos by K. Chayka taken at Battle Creek Park, Ramsey County, and Fort Snelling State Park, Hennepin County.
Have you seen this plant in Minnesota, or have any other comments about it?