Mustard family (Brassicaceae)
Description: This plant is usually a winter annual, although sometimes it is a summer annual. It consists of a rosette of basal leaves up to 9" across, from which one or more flowering stalks develop that are little branched and up to 2½' tall (although individual plants can be much smaller than this). The basal leaves are up to 4½" long and ¾" across; they are elliptic, lanceolate, or oblanceolate, and pinnately lobed. The alternate leaves on the flowering stalks are much smaller in size and widely spaced; they are lanceolate, elliptic or linear in shape, and either smooth or slightly dentate along their margins. The bases of the alternate leaves are either sessile or they clasp their stalks with auriculate (ear-like) lobes. Both the basal and alternate leaves are medium to dark green and mostly hairless, although the lower sides of their central veins are often covered with appressed hairs. The terete stalks are light green to dark reddish purple (usually the latter), and they are usually glabrous above and appressed-hairy below.
Each stalk terminates in a raceme of small flowers. These flowers bloom only toward the tip of the raceme and are short-lived. Each flower is a little less than 1/8" across and consists of 4 white petals, four greenish sepals, a pistil with a single style, and several stamens. Plants that are winter annuals bloom during spring to mid-summer, while summer annuals bloom from mid-summer to fall. The flowers are replaced by seedpods that are obcordoid, compressed (flattened), and a little less than ¼" long. Each seedpod is divided into 2 cells and contains about 20 seeds. The slender pedicels of the seedpods are about ½-¾" long and ascending. The raceme elongates with maturity and can become up to 1½' long on large plants. The small seeds are yellowish to reddish brown, ovoid-oblongoid in shape, and shiny; they can remain viable in the ground for several years. The root system consists of a taproot. This plant spreads by reseeding itself.
Cultivation: Shepherd's Purse is typically found in full sun, mesic to dry conditions, and almost any kind of soil, including cracks in pavement. The size of this plant varies considerably with the fertility of the soil and availability of moisture. It is somewhat aggressive in reseeding itself.
Range & Habitat: Shepherd's Purse is a common plant that occurs in every county of Illinois (see Distribution Map). It was introduced into North America from Europe. Habitats include fields and pastures, areas along railroads and roadsides, gardens and lawns, construction sites, vacant lots, dirt paths, and waste ground. These habitats can be either sandy or non-sandy. Shepherd's Purse is found in highly disturbed areas, often where the soil surface has been exposed.
Faunal Associations: The nectar and pollen of the flowers attract short-tongued bees (mainly Halictid and Andrenid) and various kinds of flies (including Syrphid, Tachinid, thick-headed, & bottle flies). Less often, the flowers may attract skippers and small butterflies. The caterpillars of some White butterflies have been observed feeding on the foliage of Shepherd's Purse, including Pontia protodice (Checkered White), Pieris rapae (Cabbage White), and Anthocharis midea (Falcate Orangetip). Some Pyralid moths feed on the foliage of this and other members of the Mustard family, including Eustixia pupula (Pyralid Moth sp.) and Evergestis pallidata (Purple-Backed Cabbageworm Moth). Other insect feeders include the aphids Forda formicaria and Geoica squamosa, the stinkbug Holcostethus limbolarius, and several leaf beetles (Entomoscelis americana, several Phyllotreta spp., and Psylliodes convexior). The Prairie Vole (Microtus ochrogaster) feeds on the leaves of this plant to a limited extent.
Photographic Location: Along a bike path on the campus of the University of Illinois in Urbana, Illinois.
Comments: Shepherd's Purse is an easy plant to identify among members of the Mustard family because of the distinctive shape of its seedpods. This shape apparently resembles the leather purse of shepherds during the Middle Ages. The hairiness of the flowering stalks and the shape of the leaves is rather variable across different populations of plants. Sometimes the basal leaves are deeply lobed, while on other occasions they are shallowly lobed.