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.
The leaves are both basal and stem. Basal leaves do not form rosettes and wither away very early. The lower stem leaves resemble the basal, up to 6 inches long and pinnately divided into 5 to 19 leaflets (7 to 13 the normal). These leaves are stalked and often have sparse hair. The leaflets are elliptic to ovate. The terminal leaflet the largest. The upper stem leaves are also divided but the leaflets are fewer and much narrower. The underside of the leaf rachis may have some very short fine hair. Leaves do not clasp the stem or have auricles.
The inflorescence is a terminal raceme, rather loosely organized of stalked flowers, without bracts. The raceme elongates as flowers open, typical of Mustard family plants. Smaller racemes rise from the upper leaf axils.
The flowers are each held on an ascending stalk, are 4-parted, are up to 1/4 inch long, with a tubular calyx that has 4 oblong sepals with obtuse tips; sepals are green at the base and shade to purple at the tip. The four petals are white, much longer than the sepals, spatulate in shape and have rounded tips. The reproductive parts include six stamens where two inner pairs have filaments (white) longer than an outside pair. Anthers are ovate. There is a single style with a globose shaped stigma.
Seed: Mature flowers produce a linear dry pod (called a silique), usually ascending, that contains oblong brown seeds. The pod splits open with a twist to eject seeds. Cardamine seeds usually require at least 60 days of cold stratification for germination.
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.
Names: "Bitter-cress" refers to the taste of the leaves, being less succulent and more bitter than the common water-cress (Nasturtium officinale) frequently used for salads and pots (Fernald - Ref.#6). The genus Cardamine is derived from the Greek kardamon, the Greek name for a certain cress (also in the Mustard family). The species name pensylvanica, refers to our state of Pennsylvania where the plant was originally typed. The author names for the plant classification are as follows: First to publish was ‘Muhl’ who is Gotthilf Heinrich Ernst Muhlenberg (1753-1815) a U.S. citizen and German educated botanist who produced several catalogues of plants after retiring as a Lutheran pastor. His work was updated by ‘Willd.’ which refers to Carl Ludwig Willdenow (1765-1812), German botanist, a founder of the study of the geographic distribution of plants. He was director and curator of the Botanic Garden of Berlin.
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.
Above: The upper section of the plant with the inflorescence almost fully expanded. Drawing from Britton, N.L., and A. Brown. 1913. An illustrated flora of the northern United States, Canada and the British Possessions. 3 vols. Charles Scribner's Sons, New York.
Below: The flowers have 4 spreading petals, 3 pairs of stamens and a blunt tipped style. Seed pods are long and thin containing a row of flattened seeds.
Below: Two examples of lower stem leaves.
Below: 1st photo - upper stem leaves. 2nd photo - the underside of the leaf rachis. 3rd photo - a stem section showing sparse short hair.
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.
References: Plant characteristics are generally from sources 1A, 32, W2, W3, W7 & W8 plus others as specifically applied. Distribution principally from W1, W2 and 28C. Planting history generally from 1, 4 & 4a. Other sources by specific reference. See Reference List for details.
Identification booklet for most of the flowering forbs and small flowering shrubs of the Eloise Butler Wildflower Garden. Details Here.
Friends of the Wild Flower Garden, Inc. Text and photos are by G. D. Bebeau unless otherwise credited. "www.friendsofthewildflowergarden.org"