This plant is a summer annual about 6-20" tall that branches
frequently; large specimens can be as wide as they are tall, resembling
a tumbleweed in shape. The rather stout stems are light green, terete
to slightly angular, and glabrous. Alternate leaves occur along these
stems that are 1-2" long and ¼-½" across; they are medium green,
glabrous, and oblanceolate with margins that are coarsely
crenate, shallowly lobed, or undulate. Small upper leaves often have
smooth margins. The leaves are slightly succulent with a thick texture.
The upper stems terminate in racemes of flowers about 2-10" long.
Individual flowers are up to ¼" across, consisting of 4 lavender to
white petals, 4 green sepals, 6 stamens, and a pistil with a
single style. The oblong-lanceolate sepals are about ¼" long and
glabrous, while the oblong petals spread widely during the short
period when a flower is in bloom. The ascending pedicels
The blooming period occurs from mid-summer
into the fall, lasting about 3 months. Only a few flowers are in bloom
at the same time toward the apex of the racemes. The flowers are
replaced by elongated seedpods (silicles) about ½-¾" long. Each seedpod
has a lower segment (up to ¼" long) that is ovoid-cylindrical in
shape, and an upper segment (up to ½" long) that is lanceoloid with a
long tapering beak. Between these two segments, the seedpod is slightly
constricted. The upper segment contains a single seed, while the
lower segment contains either a single seed or none. At maturity, the
upper segment of each seedpod becomes detached from the lower segment,
while the lower segment persists on the dried remains of the plant. The
upper segment can float on water, and it is often carried off by the
waves of the lake or sea. Eventually, the upper segment is deposited at
another beach, thereby introducing its seed to a new area. The seed of
the lower segment usually germinates in proximity to its mother plant,
colonizing the same beach.
The preference is full sun, moist to dry-mesic conditions, and very
sandy soil. This plant also adapts to gravelly or rocky shorelines.
The native Sea Rocket is a rare plant
in Illinois that
is state-listed as 'threatened.' Its distribution is restricted to the
shoreline of Lake Michigan in the NE section of the state (see
consist of sandy beaches and, to a lesser
extent, gravelly or rocky shorelines. Outside of the state, Sea Rocket
can be found along the shore lines of other Great Lakes (except the
northernmost areas); a closely related subspecies of Sea Rocket is also
found along the Atlantic coast.
is known about floral-faunal relationships for this plant. Similar to
other flowering plants in the Mustard family, Sea Rocket's flowers
are probably cross-pollinated by small bees, flies, beetles, and small
to medium-sized butterflies. There is a native flea beetle,
, that feeds primarily, if not exclusively,
on the foliage of Sea Rocket: its larvae form mines through the
leaves. Other flea beetles that feed on the foliage of this plant
(introduced from Europe), Phyllotreta
, and Phyllotreta
(Clark et al., 2004). Larvae of
a moth, the Rubbed Dart (Euxoa
also referred to as the Sandhill Cutworm, feed primarily on
the underground parts of Sea Rocket and many other plants in sandy
areas (Covell, 1984/2005).
A sandy beach at Indiana Dunes State Park in NW
This member of the Mustard family is quite unique and easy to identify:
it has slightly succulent leaves and unusual seedpods with 2 segments.
Rocket is a pioneer species of sandy beaches, colonizing areas that
only a few plant species can tolerate. Because its succulent leaves can
store water, it is able to withstand the desiccating effect of sunlight
and sand. The root system helps to bind and stabilize the sand, while
the decayed remnants of foliage add organic material and nutrients to
the impoverished soil. This enables other plants to colonize the beach,
beginning the process of ecological succession.