Flixweed  (Descurainia sophia)

Flixweed, sometimes called tansy mustard, is a winter or summer annual or biennial broadleaf. It is found throughout California to about 8500 feet (2600 m) and inhabits agricultural land and other disturbed areas. Flixweed can be fatally toxic to cattle when the flowering plants are consumed in quantity. Flixweed populations appear to be increasing in the Mojave Desert.

Habitat

Roadsides, fields, vineyards, orchards, agronomic crop fields, gardens, disturbed desert areas, canyon bottoms, and disturbed, unmanaged places.

Seedling

Cotyledons (seed leaves) are hairless, lance to football shaped, and small, up to 1/3 of an inch (7 mm) long. The stalk below the cotyledon is usually inconspicuous and covered with minute, branched hairs. The stalk stubs remain when the cotyledons are shed. The first leaf pair often appear opposite to one another on the stem. The first leaves are stalked, have three lobes, and are covered with tiny, branched hairs. Later leaves are one or two lobed and are alternate to one another along the stem.

Young plant

Young plants exist as basal rosettes until the flower stem develops.

Mature plant

Mature flixweed can reach over 2 feet (0.8 m) tall. Stems may be branched, starting from the middle of the main stem or above, or unbranched. Leaves are alternate to one another along the stem and are divided into leaflets (leaflets are either lobed or divided again). Leaves are sparsely to densely covered with tiny, branched hairs or a mixture of branched and simple hairs.  The similar Sisymbrium species, tumble mustard and London rocket, have simple hairs rather than the branched hairs of flixweed. Flixweed has very finely divided leaves whose leaflets are often finely divided once or twice again. However, most Sisymbrium species have undivided, lobed leaves or leaves divided into leaflets that may be lobed, but are not divided again.

Flowers

Flowers bloom from March through August, depending on the region. Erect branches have long flowering stems with yellow flower clusters.

Fruits

Fruits consist of linear, nearly cylindrical pods, about 2/5 to 1-2/5 inches (10–35 mm) long and less than 1/25 of an inch (1 mm) wide. They are straight or slightly curved upward, with a tiny beaklike tip.

Seeds

There are roughly ten to twenty seeds per pod. Seeds are tiny, less than 1/17 of an inch (1.5 mm), orange brown, and become sticky when moistened.

Reproduction

Reproduces by seed.

Related or similar plants

• Tumble mustard, Sisymbrium altissimum
• London rocket, Sisymbrium irio

More information

• Broadleaf ID illustration
• Calflora's distribution map
  
• For agriculture: UC IPM Pest Management Guidelines