Description: This adventive 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 narrowly ovate, lanceolate, or oblanceolate, and
occasionally pinnately lobed. The margin of each basal leaf is coarsely dentate
toward its tip and ciliate toward the base. The alternate leaves on the
flowering stalks are much smaller in size and widely spaced. Each of these
leaves is lanceolate or linear in shape, smooth or slightly dentate along the
margin, and sessile or clasping at the base with 2 small pointed lobes. The
flowering stalks are usually light green with fine pubescent hairs. Each stalk
terminates in a raceme of tiny white flowers. These flowers bloom only toward
the tip of the raceme and are short-lived. Each flower is about 1/10" across
and consists of 4 white petals and 4 greenish white sepals. Plants that are
winter annuals bloom during the spring to mid-summer, while summer annuals
bloom from mid-summer to fall. Each flower is replaced by a seedpod that is
triangular-obcordate, flattened, and about ¼" long. Each seedpod is
divided into 2 cells and contains about 20 seeds. The seedpods are ascending to
spreading along the raceme on slender pedicels about ½" long. The raceme
elongates with maturity and can become up to 1½' long on large plants.
The small seeds are yellowish or reddish brown, oval-oblong, 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 moisture amounts. It is somewhat
aggressive.
Range & Habitat:
Shepherd's Purse is a common plant that occurs in every county of Illinois (see
Distribution
Map). It is adventive from Europe. Habitats include fields and pastures,
areas along railroads and roadsides, gardens and lawns, construction sites,
vacant lots, and waste ground. It is found in
highly disturbed areas.
Faunal Associations: The nectar and pollen of the
flowers attract short-tongued bees (mainly Halictid and Andrenid) and various
kinds of flies (including Syrphid, Thick-Headed, Tachinid, Flesh, & Bottle
flies). Less often, the flowers may attract skippers and White 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).
Photographic Location: A lightly
mulched area near shrubbery in a parking lot at Urbana, Illinois. The size of
the plants in the lower photograph is quite large for this
species.
Comments: Shepherd's Purse
is an easy plant to identify among members of the Mustard family because of the
distinctive shape of the 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 unlobed with a few coarse
teeth.