Mustard family (Brassicaceae)
Description: This annual plant becomes about 1½–3½' tall, branching occasionally to abundantly. Initially, it forms a low rosette of basal leaves; this is followed by flowering stalks with alternate leaves. The stems are light green to purplish green, and usually glaucous; there are scattered white hairs along the lower stem(s), while the upper stems are hairless. The basal and lower alternate leaves are up to 8" long and 2" across; they are pinnatifid with several pairs of narrow lobes. The upper leaves are up to 4" long and 1½" across; they are divided into 3 lobes (a terminal lobe and 2 lateral ones) or lanceolate-ovate in shape. The upper surfaces of these leaves are dull green and hairless; their margins are irregularly dentate or shallowly cleft. The basal and lower leaves have long petioles, while the upper leaves have short petioles or they are sessile. The upper stems terminate in long slender racemes of yellow flowers up to 10" long; axillary racemes from the upper leaves are also produced. The flowers are concentrated toward the apex of each raceme, while small siliques (narrowly cylindrical seedpods) develop below. Each flower is a little less than ¼" across; it has 4 yellow petals, 4 green to yellow sepals, a stout central style, and several stamens. The siliques are less than 2/3" (17 mm.) long and stiffly erect or appressed against the central stalk of the raceme; each silique is a little wider at the base than at the apex. The typical variety of Hedge Mustard has pubescent siliques, while var. leiocarpum has glabrous siliques. The pedicels of the siliques are very short (about 1/8" or 3 mm. long). The blooming period usually occurs during the summer for about 2 months; some plants may bloom during the late spring or fall. Siliques become light brown at maturity; each silique splits in half to release several seeds. The small seeds are short-cylindrical in shape, slightly flattened, reddish brown, and about 1 mm. in length. The root system consists of a taproot. This plant spreads by reseeding itself.
Cultivation: The preference is full to partial sun, moist to slightly dry conditions, and fertile loamy soil with a high level of nitrogen. However, this weedy plant readily adapts to other kinds of soil, including those containing clay-loam or rocky material. The fertility of the soil and moisture conditions influence the size of individual plants.
Range & Habitat: Hedge Mustard is common in central and northern Illinois, but it is less common or absent in the southern section of the state (see Distribution Map). Of the two varieties of Hedge Mustard, var. leiocarpum is much more abundant than var. officinale. Hedge Mustard is originally native to southern Europe, but it has since spread to Asia, Africa, North America, and other areas of Europe. Habitats include woodland borders, degraded meadows, fields and pastures, areas along roads and railroads, barnyards, poorly maintained gardens, and waste areas. This weedy plant prefers disturbed areas with fertile soil.
Faunal Associations: Müller (1873/1883) observed the butterflies Pieris rapae (Cabbage White) and Pieris napi (Mustard White) sucking nectar from the flowers of Hedge Mustard; small bees (mainly Halictid) also visit the flowers to suck nectar and collect pollen. The caterpillars of the butterflies Pontia protodice (Checkered White) and Pieris rapae (Cabbage White) feed on many species of the Mustard family (Brassicaceae); caterpillars of moths that feed on crucifers include Eustixia pupula (Spotted Peppergrass Moth), Evergestis pallidata (Purple-Backed Cabbage Worm), Mamestra configurata (Bertha Armyworm), Plutella xylostella (Diamondback Moth), and Trichoplusia ni (Cabbage Looper). Like other crucifers, Sisymbrium spp. attract various beetles, including Entomoscelis americana (Red Turnip Beetle), Phyllotreta cruciferae (Crucifer Flea Beetle), Phyllotreta striolata (Striped Flea Beetle), and Psylliodes punctulatus (Hop Flea Beetle). An insect with a southern distribution, Murgantia histrionica (Harlequin Bug), sucks plant juices from a wide variety of crucifers.
Photographic Location: The Arboretum of the University of Illinois at Urbana-Champaign. The photographed plant is var. leiocarpum because its siliques are glabrous.
Comments: Hedge Mustard is another weedy member of the Mustard family that has been introduced from Europe. It produces long narrow racemes with erect/appressed siliques that are less than 2/3" (17 mm.) in length; this is one of its distinctive characteristics. These racemes often curve upward toward their tips, rather than remaining straight. Other Sisymbrium spp. in Illinois have siliques that are more widely spreading; in most areas of the state, these species are less common than Hedge Mustard.