Mustard family (Brassicaceae)
Description: This adventive plant is a winter or early spring annual about ½2' tall. It is more or less erect and branches occasionally. The round stems are light green and sparsely covered with short glandular hairs. The alternate leaves are greyish or bluish green and up to 2½" long and 2/3" across. They are narrowly ovate or oblanceolate, dentate and slightly undulate along the margins, and sparsely covered with short glandular hairs. The tip of each leaf is blunt or acute; it tapers gradually to a petiole-like base. The upper stems terminate in racemes of flowers up to 1' in length. Only a few flowers bloom at the apex of each raceme, while the siliques (slender seedpods) develop below. The central stalk of each raceme has a tendency to zigzag between the flowers. Each flower is about ½" across and ½" long. It consists of 4 narrow petals that are pink to purplish pink, 4 linear sepals that are purplish pink and slightly hairy, several stamens, and a pistil. The throat of this flower is quite narrow; its calyx is cylindrical, while the petals are widely spreading and form a cross. The blooming period occurs from mid-spring to mid-summer and lasts about 2-3 months. There is no noticeable floral scent. Each flower is replaced is replaced by a stout silique that curves upward and tapers to a beak. The pedicel of each silique (or flower) is quite stout and about 1/3" long. Each silique is about 11½" long when fully mature. The seeds have a smooth surface and are slightly flattened. The root system consists of a stout taproot. This plant spreads by reseeding itself.
Cultivation: The preference is full sun and mesic to dry conditions. Blue Mustard tolerates different kinds of soil, but it is more commonly found in poor soil that contains clay or gravel because of the reduced competition from other plants.
Range & Habitat: Blue Mustard is an uncommon plant that occurs primarily in NE Illinois and scattered counties elsewhere (see Distribution Map). It is originally from Asia and can be found as an adventive plant in the drier Western states, where it is more common. In Illinois, local populations usually don't persist. Habitats include areas along railroads and roadsides, stock yards, and nursery grounds. Disturbed areas are preferred.
Faunal Associations: The nectar of the flower is accessible to long-tongued bees, beeflies, butterflies, skippers, and moths. The mouthparts of other insects are too short. Little is known about this plant's relationships to birds and mammalian herbivores. The foliage is not considered to be toxic; it is possible that the seeds can pass through the digestive tracts of livestock, facilitating the dispersal of this plant to new areas.
Photographic Location: Along a roadside near Urbana, Illinois, where there was scant vegetation. This plant abruptly disappeared about a month after it was photographed. Judging from the tire tracks in the mud, it may have been run over by a truck.
Comments: Usually, members of the Mustard family have small white or yellow flowers with nectar that is accessible to insects with short mouthparts. Blue Mustard is distinctive in that each flower has narrow pink or purplish pink petals, a tubular calyx, and a small throat. Other members of the Mustard family with pink or purple flowers include Hesperis matronalis (Dame's Rocket), Lunaria annua (Money Plant). However, the flowers of Dame's Rocket and the Money Plant are larger (more than ¾" across) and their petals are more rounded. Another species in the Mustard family with similar flowers is Iodanthus pinnatifidus (Purple Rocket). However, this latter species has light blue-violet flowers, glabrous stems, and broader leaves toward the base of the plant that are pinnately lobed or ovate with serrated margins. The siliques of Purple Rocket lack a beak and they are more straight than the siliques of Blue Mustard.