Descurainia sophia (L.) Webb
Family - Brassicaceae
Stems - To 1m tall, herbaceous, stellate and simple pubescent, from thick taproot, branching above at inflorescence.
Leaves - Alternate, to 14cm long, 6-7cm broad, pinnate, dense stellate pubescent, reduced upward, sessile. Leaflets divided, those divisions again divided or lobed. Ultimate leaf divisions entire.
Inflorescence - Terminal racemes, compact in flower, much elongating in fruit to +30cm long.
Flowers - Petals 4, yellow, 3-4mm long, 1mm broad, spatulate, recurving slightly at apex. Stamens 6, exserted. Filaments to 4mm long. Ovary terete, 2-3mm long. Sepals 4, yellow-green, glabrous, 3mm long, -1mm broad, linear.
Fruit - Silique to 2.5cm long, 1mm in diameter, many seeded. Pedicel to 1.5cm long, filiform.
Flowering - May - July.
Habitat - Waste ground, disturbed sites, roadsides, railroads.
Origin - Native to Europe.
Other info. - D. sophia is becoming common in this state and others. I first found it in Florida. The plant is easy to ID in the field because of the much divided leaves, densely pubescent stems, and ascending long fruits. D. pinnata, a native species, looks similar but has shorter fruits, glandular pubescent stems, and leaves which are slightly less divided.
Photographs taken off Highway 9, Platte County, MO., 5-2-00.