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Santiago Baker
Santiago Baker

Bitter Cress

Little bittercress is a winter or summer annual (and sometimes biennial) broadleaf. In California, it is considered a desirable floral community member in natural settings, but is sometimes weedy in disturbed places such as landscaped areas, orchards, nurseries, turf, and vegetable crops. Little bittercress is found up to an elevation of about 2600 feet (800 m) in the Klamath Ranges, North Coast Ranges, San Francisco Bay region, Sacramento Valley, and likely other California areas, as its range is expanding.

bitter cress

It is not known how narrow-leaved bitter-cress came to the United States from Europe. However, the first record of the plant in New England was from Peterboro, New Hampshire in 1916. The plant then appeared in Connecticut, followed by a subsequent spread across Connecticut, and later reports from Massachusetts (1991), Vermont (1992), and Acadia National Park in Maine (1994).

This community occurs in and immediately adjacent to springs. Springs are places where groundwater flows to the surface, and eventually coalesces into a channel of flowing water. Water flow is relatively constant and uniform in temperature. Golden saxifrage (Chrysosplenium americanum), Pennsylvania bittercress (Cardamine pensylvanica), and the exotic species watercress (Nasturtium officinale) are often the most dominant plant species. Other species may include horsetails (Equisetum sp.), lettuce saxifrage (Saxifraga micranthidifolia), mountain watercress (Cardamine rotundifolia), and spring cress (Cardamine bulbosa). There is often high cover of bryophytes (mosses and liverworts) in and around the spring.

Rapidly invading forested areas along rivers in eastern Minnesota, narrowleaf bittercress is raising concerns about its invasive potential. It is not known how narrowleaf bittercress was introduced to North America from Eurasia. It was first reported in the US in New England in 1916. The first report in Minnesota was in 2008. By 2009, multiple discrete infestations were reported in several counties.

Commonly, narrowleaf bittercress is found in forested floodplains and along rivers and streams in both its native and naturalized ranges. Occasionally, isolated populations occur in dry, sunny areas away from water.

Narrowleaf bittercress can self-pollinate and produces prolific quantities of seed in siliques that can shoot the seed a short distance from the plant when the dried seedpods burst open. Thus, a single plant can quickly form a colony. Seeds can germinate in water and rivers and streams are considered a method of long-range dispersal. Seeds can also be moved by human, animals, and vehicles.

Narrowleaf bittercress is reported in the northeastern United States and New Brunswick and Ontario in Canada. In Minnesota, observant botanists, natural resource specialists, and vegetation management consultants reported narrowleaf bittercress spreading at alarming rates in Hennepin, Ramsey, Washington, and Winona counties. Most infestations are located adjacent to either the St. Croix or Mississippi River.

Narrowleaf bittercress outcompetes desirable vegetation which may result in decreased species diversity and habitat quality. The full impact of narrowleaf bittercress remains unknown due to the newness of most infestations in North America. Narrowleaf bittercress proliferates and spreads very quickly, provoking apprehension that it may prove highly invasive. The experience of other states with this species provides a basis for concern. Narrowleaf bittercress is established in New England. It was recently assessed and ranked as highly invasive plant in New York and a noxious weed in Connecticut and Massachusetts.

For a plant in the mustard family, spring cress bears rather showy flowers. They are visited by a variety of insects, which gather nectar and often pollinate the plant, too. Nearly all the members of the mustard family, including broccoli and radishes, have flowers with four petals.

An inconspicuous native annual or biennial of moist sites, the young stems and leaves of Pennsylvania bitter-cress are edible. Along with non-native bitter-cresses, Pennsylvania bitter-cress is weedy in nurseries and greenhouses.

Wavy bitter-cress is native to Europe and eastern Asia, and introduced in North America. The North American occurrences are made up of two distinct entities--the European and the Asian wavy bitter-cress are genetically different, although there is as yet no reliable way to distinguish between them based on morphology.

Similar to Hairy Bitter-cress but the stems are likely to be hairy, at least in the lower half, and are quite often branched and wavy (flexuous). Flowers are white with 6 stamens (Hairy Bitter-cress has four stamens). The seed pods don't usually extend beyond the flowers, unlike Hairy Bitter-cress.

Narrowleaf bittercress generally grows in forested areas, often near waterways, and has been observed outcompeting native vegetation. Narrowleaf bittercress is fairly new to Minnesota and its distribution and impacts are not thoroughly understood. Any potential sightings should be reported to the Minnesota Department of Agriculture.

When narrowleaf bittercress germinates it grows as a round grouping of leaves (rosette) near the ground. In most cases it stays as a rosette for the first year and then in its second year it sends up a flowering stalk, flowers, and dies. In some cases the first year plant sends up a flowering stalk. Flowering stalks can grow up to 2.5 feet tall and have small white flowers with four white petals or no petals visible.

When narrowleaf bittercress germinates it grows as a round grouping of leaves (rosette) near the ground. The rosette leaves have 3-11 leaflets that are round with lobes. In most cases it stays as a rosette for the first year and then in its second year it sends up a flowering stalk, but in some cases the first year plant sends up a flowering stalk. The flowering stalks can grow up to 2.5 feet tall. Leaves are alternate (come off the stem one at time at each leaf node). Leaves have 6-20 leaflets that are more linear and less lobed than the rosette leaflets. At the point where the leaf attaches to the stem there are small green growths called "auricles" that grasp the stem and look like two small points extending away from the stem.

When narrowleaf bittercress germinates it grows as a round grouping of leaves (rosette) near the ground. In most cases it acts as a biennial and stays as a rosette for the first year and then in its second year it sends up a flowering stalk, flowers, and dies. In some cases it acts as an annual and the first year plant sends up a flowering stalk. Narrowleaf bittercress is commonly found in forest understories and near waterways, but can occasionally be found in more open, sunny areas.

Narrowleaf bittercress is native to Europe and Asia and it is not clear how it was introduced to the United States. It was first found in the northeastern United States in 1916 and first confirmed in Minnesota in 2008. Narrowleaf bittercress seeds can be spread by water, humans, animals, and equipment.

Narrowleaf bittercress is a Minnesota Department of Agriculture Prohibited Noxious Weed on the Control List meaning that efforts must be made to prevent the spread of seeds or other propagating parts. Additionally no transportation, propagation, or sale is allowed.

Pennsylvania Bitter-cress is a native annual or biennial forb growing 6 to 24 inches high on an erect to spreading stem that is usually unbranched but may do so at the top. Stems may have a few hairs and may take on a reddish color in full sun.

Habitat: Pennsylvania Bitter-cress grows from a fibrous root base lacking rhizomes. It propagates by re-seeding. It requires moisture, rich soils, full to partial sun is needed up to flowering. These habitats include wetlands, ditches, stream banks, moist bottomlands and moist uplands.

Comparisons Pennsylvania Bitter-cress is of the same genus as two of our favorite Spring flowers - Two-leaved Toothwort, C. diphylla, and Cut-leaved Toothwort, C. concatenata. The flowers on those two species are similar but they are perennial, have rhizomes, and the leaves differ. The imported Watercress, Nasturtium officinale, grows in the same areas but has more glossy deep green leaves and the leaflets are more broad. Yellow Rocket, Barbarea vulgaris, is a similar looking but larger plant, and there the flowers are yellow and the leaves clasp the stem with auricles.

Notes: Pennsylvania Bitter-cress is not indigenous to the Garden but native to the area. Eloise Butler's records show that she obtained plants of this species on April 12, 1915 from Minnehaha Park in Minneapolis. It has presumably been in the wetland ever since. It is native to the majority of counties in Minnesota with most exceptions being in the SW quadrant. The plant has an extensive range in North America, being found everywhere except the very far north of Canada and in Arizona.

There are 6 native species of Cardamine found in Minnesota: C. bulbosa, Spring cress; C. concatenata, Cut-leaved Toothwort; C. impatiens, Narrowleaf Bittercress; C. parviflora, Small-flowered Bittercress; C. pensylvanica, Pennsylvania Bittercress; and C. pratensis, Cuckoo Flower. Some sources include C. diphylla but the U of M reports there are no collected specimens.

  • Small, rosette-based annual up to 25 cm tall

  • Leaves are deep green, lobed and sparsely hairy. Each leaf has two or three pairs of rounded leaflets with a larger terminal lobe

  • Upright flower stems carry few leaves and many tiny white flowers in small clusters

  • Flowers are 4-5 mm across with four petals, each twice as long as the four sepals, and four stamens with yellow anthers

  • Flowers are followed by small, slender, upright pods 15-25 mm long. Two valves split explosively and coil upwards, spreading the seeds up to a metre from the parent plant.

  • Similar speciesWavy bitter cress (Cardamine flexuosa) is similar but often slightly larger with a wavy erect stem and six stamens in the flower. It is scattered throughout New Zealand and found in wetter environments than bitter cress

  • The native New Zealand bitter cress (Cardamine debilis) is similar to bitter cress but has larger flowers, each with six stamens. It is found throughout New Zealand, in a range of forest or tussock habitats

  • Cuckoo cress (Cardamine pratensis) is a rhizomatous perennial herb up to 60 cm tall. It has larger pink flowers and is found in wet places and along river banks in Northland, Auckland, Waikato, Manawatu and Horowhenua in the North Island and in Westland and Southland in the South Island.



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