Mustard family (Brassicaeae)
Description: This perennial wildflower is 4-12" tall and unbranched, except for possibly 1-2 flowering side stems near the apex. The erect central stem is light green to purplish green, terete, and hairy. At the base of each plant, 1-2 basal leaves are commonly present; they are about 1" long and across, cordate-orbicular, and bluntly dentate or undulate along their margins. Each basal leaf has a long slender petiole. The alternate leaves are up to 2" long and 1" across; they are oval-ovate to oblong, bluntly dentate or undulate along the margins, and ciliate. At the base, the alternate leaves are sessile or slightly clasp the central stem. The alternate leaves become slightly shorter and more narrow as they ascend the stem. The central stem terminates in a raceme of flowers. The flowers and buds are concentrated toward the apex of the raceme, while cylindrical seedpods (siliques) develop along the remainder of the raceme. Each flower is about ½–¾" across, consisting of 4 petals, 4 sepals, several stamens, and a single stout style of the pistil. The petals are pale purple or purple-tinted white and obovate in shape. The sepals are purple, hairy, and membranous-white along their margins. The petals are much longer than the sepals. The blooming occurs during mid-spring and lasts about 2 weeks. The flowers are fragrant. Each flower is replaced by an ascending silique up to 1" long. The 2-valved siliques are green to purple; each silique contains a single row of seeds and it has a stout pedicel up to 1" long at its base. Eventually, the silique splits in half lengthwise to release the seeds. The root system is fibrous and tuberous.
Cultivation: This wildflower develops early during the spring when it receives dappled sunlight from its location underneath deciduous trees. It likes an evenly moist site with fertile loamy soil and abundant leaf mold. By the beginning of summer, it has already died down and released its seeds.
Range & Habitat: The native Purple Cress is occasional in NE and east central Illinois, but it is rare or absent elsewhere in the state (see Distribution Map). Habitats include moist deciduous woodlands, low wooded valleys, and areas along shaded seeps and springs, particularly where limestone comes close to the surface of the ground. This conservative species is normally found where the original ground flora is still intact. It is one of the spring wildflowers in woodlands that is threatened by the spread of Alliaria petiolata (Garlic Mustard).
Faunal Associations: Records about floral-faunal relationships for this species are limited. Insect visitors of the flowers are probably similar to those of a closely related species, Cardamine bulbosa (Spring Cress), which blooms only a little latter and occupies similar habitats. These insects include various kinds of bees (honeybees, mason bees, Andrenid bees, Halictid bees), bee flies (including Bombylius major, the Giant Bee Fly), other miscellaneous flies, and butterflies that appear during the spring. Most of these insects suck nectar from flowers, although some of the bees and flies also seek pollen. An oligolectic flea beetle that prefers woodland habitats, Phyllotreta bipustulata, feeds on the foliage of Purple Cress; it also feeds on the foliage of Dentaria spp. (Toothworts). Mammalian herbivores rarely feed on this wildflower because its foliage is short-lived and unpleasant-tasting (bitter and spicy).
Photographic Location: Along a shaded seep in Vermilion County, Illinois.
Comments: This is another lovely spring wildflower of the woodlands. Purple Cress is similar to Cardamine bulbosa (Spring Cress), except that the latter has flowers with white petals and green sepals. Spring Cress also has a glabrous central stem, while Purple Cress has a hairy stem. In contrast to Dentaria spp. (Toothworts) and many other Cardamine spp. (Bitter Cress species), both of these wildflowers lack compound leaves that are pinnately or palmately divided. Another species of the Mustard family, Iodanthus pinnatifidus (Purple Rocket), produces pale purple flowers on long racemes in damp wooded areas. However, Purple Rocket is a larger plant that blooms later in the year (late spring to mid-summer). Other common names of Cardamine douglassii are Purple Spring Cress and Northern Bitter Cress.