Narrowleaf bittercress (Cardamine impatiens)

Common Names: Bushy rock-cress

Description:

Narrowleaf bittercress (Cardamine impatiens) is a small white-flowered plant in the mustard family, native to Europe and Asia [1][3]. It was first found in the United States in 1916 and has since spread into shaded woodlands, riverbanks, and floodplains, where it forms dense carpets that crowd out native wildflowers [1][2]. MISIN tracks it as an early-detection species because a single plant can fling thousands of seeds, letting a small patch take over a forest floor quickly [2].

Habit:

Narrowleaf bittercress is a knee-high to waist-high plant, usually up to about 2.5 to 3 feet tall, in the mustard family [1][2]. Its leaves are divided into many small leaflets along a central stalk, like a feather ? the low first-year rosette has 3 to 11 rounded, lobed leaflets, while the taller flowering stems carry 6 to 20 narrow, pointed leaflets [1][2]. The surest clue is at the base of each stem leaf: two narrow, pointed flaps called auricles wrap around and clasp the stem, like little ears grabbing the stalk ? no native bittercress has them [1][2]. The flowers are tiny (about 1/10 inch), white, with four petals that are often so small they look missing [1][2].

It is easiest to spot from late spring into summer (about May to August), when the flowering stems are up and, soon after, the slender seed pods line the stems [1][2]. Look on shaded, moist ground ? forest floors, wooded trails, and stream and river banks [1][2]. First-year plants are just a low rosette of leaves that stays green into winter, so a spot can hold the plant even before the tall stems appear [1][2].

At-a-glance cues:

1. Two narrow, pointed flaps (auricles) clasp the stem at the base of each stem leaf [1][2]
2. Leaves divided feather-like into many small leaflets ? 3 to 11 on the low rosette, 6 to 20 on the flowering stem [1][2]
3. Tiny white four-petaled flowers, the petals often so small they look missing [1][2]
4. Slender, upright seed pods that line the stem and burst open when ripe [1][2]

Leaves:

1. Arrangement: alternate along the stem; feather-like (pinnately compound), divided into many small leaflets [1][2]
2. Rosette leaves: 3 to 11 rounded, lobed leaflets in a low first-year cluster [1][2]
3. Stem leaves: 6 to 20 narrow, pointed, often lance-shaped leaflets [1][2]
4. Base: two narrow, pointed flaps (auricles) that clasp the stem where the leaf attaches ? the key identifying trait [1][2]

Stems:

1. Habit: an upright, herbaceous (non-woody) annual or biennial, up to about 2.5 to 3 feet (0.8 to 0.9 m) tall [1][2]
2. Root: a taproot that is shallow enough to pull up easily [1]
3. Form: first-year plants are a low rosette of leaves; second-year plants send up the leafy flowering stem [1][2]

Flowers:

1. Color: white [1][2]
2. Form: tiny, about 1/10 inch (2.5 mm), with four petals that are often reduced or missing [1][2]
3. Arrangement: in small clusters at the tops of the stems [1][2]
4. Bloom time: late spring into summer, about May to August [1][2]
5. Pollination: the flowers are self-pollinating, so a single plant can set a full crop of seed on its own [2]

Fruit and seeds:

1. Fruit: a long, slender, upright seed pod (a mustard-family silique), up to about 0.8 inch (2 cm) long, lining the stem [1][2]
2. Dispersal: when ripe, the pods burst open and shoot the seeds several feet from the plant [2]
3. Output: a single plant can produce up to about 5,500 seeds [2]
4. Spread: seeds are also carried farther in water and on animals, shoes, and equipment [1]

Habitat:

Narrowleaf bittercress grows on shaded, moist ground ? forest understories, moist woodlands, floodplains, and the banks of streams and rivers ? and it can also turn up in meadows and more open, sunny spots [1][2]. It favors part shade to full shade and moist soil, which lets it thrive on the forest floor where many garden and farm weeds cannot [2].

It is native to Europe and Asia and was first recorded in the United States in 1916 [1][3]. Because it tolerates shade and disturbance, it spreads readily along trails, roadsides, and waterways into otherwise healthy woods [1][2].

Reproduction:

Narrowleaf bittercress spreads only by seed, but it makes a lot of seed and flings it hard [2]. When the slender pods ripen, they snap open and shoot seeds several feet from the plant, and a single plant can produce up to about 5,500 seeds ? so one plant can seed a wide patch in a single year [2]. Seeds then travel farther in running water and by hitching a ride on animals, shoes, tires, and tools, which is how the plant reaches new woods and stream banks [1].

The plant is an annual or biennial [1][2]. Biennial plants spend their first year as a low rosette of leaves that stays green into winter, then send up a flowering stem the second year, set seed, and die; some plants race through the whole cycle in a single year [1][2]. The flowers are self-pollinating, so even one isolated plant can produce a full seed crop [2]. Because everything rides on that seed, control means pulling plants before the pods ripen and burst ? and returning for several years to catch new seedlings [1][2].

Impact and Damage:

Narrowleaf bittercress is not known to harm people, pets, or livestock, and it does not sting or burn [1]. Its problem is how it takes over shaded ground [1][2].

On the forest floor, it grows into dense cover that crowds out native wildflowers and tree seedlings, lowering the variety of plants and the quality of woodland wildlife habitat [1][2]. Because it tolerates shade, it can invade otherwise intact, healthy woods ? not just disturbed edges ? and its explosive, high-volume seeding lets small patches expand into large stands fast [1][2]. On floodplains and stream banks, water carries the seed downstream to start new infestations [1]. No dollar figure for its damage in North America has been established.

Similar species:

Narrowleaf bittercress is easily confused with a few other plants, especially other members of the mustard family. These comparisons come from published sources, since MISIN does not yet track look-alikes for it. The clasping ear-like auricles at the base of the stem leaves are the surest way to tell it apart [1][2].

Garlic mustard (Alliaria petiolata) is another invasive mustard that shares a first-year rosette and tiny white four-petaled flowers, but its leaves are simple, heart- to kidney-shaped, and scalloped ? not divided into many leaflets ? and its crushed leaves smell of garlic [1].

Pennsylvania bittercress (Cardamine pensylvanica) is a native bittercress with similar feather-divided leaves and tiny white flowers, but it lacks the narrow, stem-clasping auricles that narrowleaf bittercress has at its leaf bases [1][2].

Hairy bittercress (Cardamine hirsuta) is a common weedy bittercress with a low rosette and tiny white flowers, but it stays small and ground-hugging and also lacks the stem-clasping auricles of narrowleaf bittercress [1][2].

Monitoring and rapid response:

Signs to watch for:

1. Feather-leaved plants up to 2.5 to 3 feet tall on shaded, moist ground ? forest floors, trails, and stream banks ? with narrow ear-like flaps clasping the stem at each leaf base, tiny white flowers in late spring to summer, and slender upright seed pods soon after [1][2].

What you can do:

1. Pull plants by hand ? the shallow taproot comes up easily ? before the seed pods ripen and burst [1][2]. Late spring through early summer, before pods mature, is the best time.
2. Bag the pulled plants and put them in the trash; do not compost them and don't leave them on the ground, since pods can still ripen and fling seed [1][2].
3. Because ripe pods shoot seed several feet and seeds travel in water and on gear, brush seeds off your boots, tools, and pets before leaving an infested spot [1].
4. Check the same area each year for several years and pull new plants and rosettes, since seeds keep sprouting after the first cleanup [1][2].
5. For crews and land managers: find and remove small, outlying patches first ? especially upstream and along trails ? before they seed into clean woods, and coordinate repeat visits across the whole site because water and foot traffic keep moving seed [1][2].

When to call a professional:

1. Large, well-established stands, or infestations spread along a stream or river where hand-pulling can't keep up [1][2].
2. For chemical control options, contact a licensed applicator or your local cooperative extension office.

Report sightings to MISIN. Help track this species' spread by submitting observations through the MISIN web site or the MISIN mobile app (Android, iOS, Windows, and macOS). Photos at multiple angles paired with a precise GPS location are the most valuable data for confirming new occurrences and triggering rapid-response review.

Credits:

1. Minnesota Department of Natural Resources. Narrowleaf bittercress (Cardamine impatiens). dnr.state.mn.us
2. University of Minnesota Extension. Narrowleaf bittercress. extension.umn.edu
3. USDA NRCS PLANTS Database. Cardamine impatiens L. plants.usda.gov

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