Description: This adventive
winter annual is about 1-2' tall, branching occasionally. The variable stems
are round, angular, or ridged; they are rather stout and have short appressed
hairs. The basal leaves form a low rosette spanning about 6" across. They are
broadly linear (usually broadest toward the middle), and dentate with widely
spaced teeth or shallowly lobed along the margins. Like the stems, they have
short appressed hairs. The cauline leaves alternate along the stems. They are
similar to the basal leaves, although less likely to be lobed, and span up to
3" in length and 2/3" across. Sometimes the leaves have a shiny upper surface
and their margins are curly or undulate. The upper stems terminate in racemes
of flowers. Each flower is about ¼" across when fully open and about
1/3" long. It consists of 4 petals that are yellow or bicolored (white near the
throat of the flower, yellow toward the tips of the petals), 4 green sepals
that are linear-lanceolate, and several stamens with dull brown anthers, and a
pistil with a stout style. The petals are longer than sepals, and they become
very narrow toward the base of the flower. The pedicel of each flower is about
1/3" long and quite stout. The blooming period occurs from mid-spring to early
summer and lasts about 1-2 months. Each flower is replaced by a silique
(slender seedpod) that is 2-4" long when fully mature and cylindrical in shape.
This silique may be angular or round in cross-section. The siliques are widely
spreading to ascending and almost resemble slender stems. The small seeds are
oblongoid and brown. The root system consists of a taproot that is often stout.
This plant spreads by reseeding itself.
Cultivation: This adaptable plant prefers full sun,
slightly moist to dry soil, and tolerates different kinds of soil; it often
occurs in fertile loam or clay loam. Most vegetative growth occurs during the
spring.
Range & Habitat: Treacle
Mustard occurs occasionally in scattered counties throughout Illinois (see
Distribution
Map). It may be locally common in some areas. Habitats include fields,
construction sites, vacant lots, areas along railroads and roadsides, and
miscellaneous waste areas. It prefers areas where the soil has been recently
disturbed. Treacle Mustard is native to Eurasia.
Faunal Associations: Little is known about this
particular plant's relationships to fauna. The flowers probably attract various
kinds of small bees, flies, and White butterflies, like other members of the
Mustard family. Some Erysimum spp., such as Erysimum
cheiranthoides (Wormseed Mustard), have bitter-tasting foliage and seeds
that probably discourage their consumption by mammalian
herbivores.
Photographic Location:
Disturbed soil near a parking lot where construction activity was taking place
at the Champaign County Courthouse in Urbana, Illinois. The upper photograph
shows the form of Treacle Mustard with plain yellow flowers. The siliques in
the upper photograph are still immature and not fully grown.
Comments: Other common names for this plant are
'Spreading Wallflower' and 'Bushy Wallflower.' It is in the same genus as the
native Erysimum capitatum (Western Wallflower), which has much showier
flowers (about ¾" across). Generally, Erysimum spp. have flowers
with long narrow sepals and cylindrical siliques. The size of the flowers for
this group of plants is highly variable. Treacle Mustard differs from other
Erysimum spp. in Illinois by its long spreading siliques (about 2-4" in
length) on short stout pedicels (about 1/3" long). Other Erysimum spp.
have shorter siliques (less than 2" in length) on slender pedicels; their
siliques are often held more erect and closer to the central stalk of the
raceme. The Western Wallflower also has long siliques (up to 4" in length), but
its flowers are much larger than those of Treacle
Mustard.