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.