Cardamine impatiens (Narrow-leaf Bittercress)
|Also known as:
|part shade, shade; moist woods, thickets, stream banks
|May - July
|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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Elongating clusters of stalked flowers at the top of the plant and at the tips of branching stems, with open flowers in small clusters at the tip and fruit forming below. Individual flowers are white to greenish, tiny with 4 petals but these are often absent or indistinct.
Leaves and stem:
There are both basal and alternate stem leaves. Stem leaves are compound with 13 to 25 leaflets, to ~6 inches long. Leaflets are generally lance to narrowly egg-shaped with an asymmetrical base and have a minute stalk; the edges may be smooth, jagged or sharply toothed. The terminal leaflet is largest, 3/8 to 1½+ inches (1 to 4+ cm) long
Basal leaves are compound with 3 to 11 leaflets that have asymmetric bases and rounded lobes that may be further notched or lobed. Leaves and stems are hairless. The basal rosette is produced the first year and flowering stems are usually produced the second year.
Fruit is a straight slender pod, mostly ascending, up to about 1 inch (1.6 to 3+ cm) long. Ripened pods burst open and can shoot seed several feet from the mother plant, thus it can form dense colonies fairly quickly.
Narrow-leaf Bittercress is a relatively new exotic species in Minnesota, and quite 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. It has been found along waterways and especially along trails, very likely via hikers, bikers and dog walkers spreading weed seed when travelling 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 Prohibited Control 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.
It resembles some other Cardamine species, most notably Pennsylvania Bittercress (Cardamine pensylvanica), but the latter has larger and better defined flowers, lacks the auricles on stem leaf stalks, leaflets often (not always) have no stalk, and stems are usually at least sparsely hairy, especially near the base. Note that I did see reports of C. impatiens on both iNaturalist and EDDMapS that are incorrectly IDed and are actually C. pensylvanica, so the real distribution and abundance of this weed are not known, but that's true for virtually all weeds.
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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?