Green-Flowered Peppergrass
Lepidium densiflorum
Mustard family (Brassicaceae)

Description: This plant is usually a winter annual; less often, it is a summer annual or biennial. It overwinters as a low rosette of basal leaves up to 6" across. Individual basal leaves are up to 3" long and " across; they are variably pinnatifid and hairless to mostly hairless. During the spring and early summer, this plant develops branching stems with alternate leaves. A robust specimen is about 1' tall, 2' across, and rather bushy in appearance; however, specimens at barren sites are typically less branched and smaller in size. The stems are light green to reddish green and glabrous (or nearly so). The alternate leaves are up to 2" long and " across; they are medium green, linear to linear-oblong in shape, smooth or slightly dentate along their margins, glabrous, and sessile. Unlike the basal leaves, none (or very few) of the alternate leaves are pinnatifid.

The upper stems terminate in elongated racemes that have abundant flower buds, flowers, and seedpods (silicles). These racemes eventually become about 3-4" long. The flower buds at the apex of each raceme are often slightly pink or red, particularly in bright sunlight. The greenish flowers are about 1/8" (3 mm.) long and inconspicuous. Each of these flowers has 4 tiny white petals (or none), 4 linear green sepals, a pistil with a single style, and 2 or more stamens. The petals, if present, are smaller than the sepals. The slender pedicel of each flower is about " long. The blooming period usually occurs from late spring to mid-summer, although some plants will bloom later in the year. Each flower is replaced by an orbicular 2-celled seedpod (or silicle) about 1/6" (4 mm.) long and across; this seedpod is flattened and it has a tiny notch at its apex. Each cell of this seedpod contains a single seed. The seedpods are light enough be blown about by the wind, thereby distributing the seeds. The root system consists of a taproot.

Cultivation: This weed prefers full sun, mesic to dry conditions, and fertile loamy soil, although it also adapts readily to rocky or sandy soil. The size of individual plants is strongly affected by soil fertility and moisture conditions.

Range & Habitat: Green-Flowered Peppergrass is occasional to locally common in central and northern Illinois, while in southern Illinois it is less common. It was introduced accidentally into North America from Eurasia. Habitats include degraded prairies and glades, cultivated and abandoned fields, areas along railroads and roadways, vacant lots, and waste areas. This plant typically occurs in disturbed habitats where the topsoil is exposed. It does not invade high quality natural habitats to any significant degree.

Faunal Associations: Generally, the flowers of Lepidium spp. (peppergrasses) attract small bees (Halictid, masked, little carpenter bees) and various flies (especially Syrphid flies). These insects seek nectar and pollen from the flowers. The caterpillars of the butterflies Anthocharis midea (Falcate Orangetip) and Pontia protodice (Checkered White) occasionally feed on peppergrasses, as do the caterpillars of Eustixia pupula (Snout Moth sp.). The foliage of this group of plants has a peppery taste from mustard oils in varying degrees, which may provide some protection from mammalian herbivores.

Photograph Location: A cultivated field near Champaign, Illinois.

Comments: This is one of many members of the Mustard family that has been introduced from Eurasia. In Illinois, Green-Flowered Peppergrass is primarily an agricultural weed. Distinguishing this species from other Lepidium spp. (peppergrasses) can be difficult. Key characteristics to look for include the following: 1) The petals of the flowers are shorter than the sepals and inconspicuous, or they are absent altogether, 2) the flower buds are often slightly pink or red in bright sunlight, 3) the alternate leaves of the stems are rarely pinnatifid, 4) the foliage is hairless, or nearly so, and 5) the crushed foliage lacks a foul odor. The only other species in this genus that has petals smaller than the sepals (or that are absent altogether) is Lepidium ruderale (Stinking Peppergrass). This latter species is rarely seen in Illinois. Unlike Green-Flowered Peppergrass, it has pinnatifid alternate leaves and foul-smelling foliage. Other members of the Mustard family can be distinguished from the peppergrasses by the shapes of their seedpods or their yellow flowers.