Pennsylvania Bitter Cress
Mustard family (Brassicaceae)
Description: This native plant is a winter annual or biennial up to 2½' tall that branches occasionally. A few basal leaves are produced during the fall, while alternate cauline leaves develop along the stems during the following spring. These leaves are up to 3½" long and ½" across (if not larger); they are pinnately compound with 3-15 leaflets. The leaflets are linear, oblanceolate, obovate, or orbicular in shape, becoming more narrow on the upper leaves; their margins are usually undulate, shallowly lobed, or dentate with a few blunt teeth. On each leaf, the terminal leaflet is as wide or wider than the remaining leaflets. Both the leaves and stems are green and glabrous. The upper stems terminate in racemes of small white flowers. Each flower is about 1/8" long, consisting of 4 white petals, 4 light green sepals, a stout pistil, and several stamens. The pedicels are longer than the flowers and rather stout. The blooming period occurs from early spring to early summer and lasts about 2 months. Each flower is replaced by a cylindrical seedpod (or silique) that is up to 1½" long. The siliques are stiffly erect and they spread outward slightly from the central stalk of their racemes. The tips of young siliques typically surround the flowers and partially obscure them. Each silique contains a row of small seeds. The root system consists of a tuft of shallow fibrous roots. This plant spreads by reseeding itself.
Cultivation: The preference is light shade to partial sun, moist conditions, and a rich loamy soil. This plant develops quickly during the spring when the weather is cool and moist.
Range & Habitat: Pennsylvania Bitter Cress occurs occasionally in most areas of Illinois; it tends to be less common or absent in the NW corner of the state (see Distribution Map). Habitats include wet to mesic deciduous woodlands (especially floodplain woodlands), swamps, shady seeps and springs, the bottom of cliffs, and areas along woodland paths. Occasionally, this species is found in more disturbed areas that are moist and partially shaded.
Faunal Associations: Occasionally, small bees or flower flies visit the flowers, otherwise they attract few visitors. The caterpillars of Evergestis pallidata (Purple-Backed Cabbage Worm Moth) are known to feed on Cardamine spp. (Bitter Cresses). Information about floral-faunal relations with birds and mammals is currently unavailable.
Photographic Location: Along a woodland path at Allerton Park in Piatt County, Illinois.
Comments: This spring wildflower of woodlands is not very showy and often overlooked. It has a similar appearance to other Bitter Cresses with small white flowers, including Cardamine hirsuta (Hairy Bitter Cress) and Cardamine parviflora arenicola (Small-Flowered Bitter Cress). Hairy Bitter Cress, an introduced species, is hairy toward the base and it has abundant basal leaves while the flowers are blooming. Pennsylvania Bitter Cress has very few, if any, basal leaves while the flowers are blooming, and its foliage is completely hairless (at least in Illinois). Small-Flowered Bitter Cress is usually a little smaller in size than Pennsylvania Bitter Cress and it has more narrow leaflets (up to ¼" across). The terminal leaflets of this species are about the same size as the non-terminal leaflets. Small-Flowered Bitter Cress is usually found in habitats that are drier and sunnier than Pennsylvania Bitter Cress, although it is occasionally found in moist woodlands and wetlands as well.