Descurainia sophia (L.) Webb ex Prantl
CC = *
CW = 5
MOC = 11
Family - Brassicaceae
Habit - Annual or biennial forb.
Stem - Erect, 25-80 cm long, moderately to usually densely pubescent with many-branched, nonglandular hairs.
Leaves - Alternate, pinnately compound, short petiolate or sessile. Blades 1-15 cm long, moderately to usually densely pubescent with many-branched hairs, 2 or 3 times pinnately dissected, the leaflets toothed and oblanceolate to linear, the upper leaves progressively reduced and less divided.
Inflorescences - Racemes or less commonly panicles, the flowers often not subtended by bracts.
Flowers - Sepals 4, lanceolate to ovate, ascending to erect, 2.0-2.5 mm long. Petals 4, 2.0-2.5 mm long, pale yellow. Styles absent or less than 0.5 mm long.
Fruits - Siliques, 15-25 mm long, 0.5-1.2 mm wide, tapered and pointed at the tip, the valves with a prominent midnerve, the septum with 2 or 3 longitudinal veins, the fruits and their stalks ascending. Styles absent to 0.2 mm. Seeds 20-40 per fruit, in 1 row in each locule.
Flowering - May - July.
Habitat - Fields, roadsides, pastures, open disturbed areas.
Origin - Native to Eurasia.
Lookalikes - D. pinnata.
Other info. - This introduced mustard is uncommon in Missouri, known from only a few widely scattered locations. It is much more common to our west, occurring in nearly every county of every state in the western half of the continental U.S. The plant is easily identified by its small, pale yellow flowers and its frilly, highly dissected foliage. The stems and leaves are usually somewhat canescent (grayish due to hairiness). The far more common species in Missouri is tansy mustard, Descurainia pinnata, which differs by having much shorter fruits.
Photographs taken near Three Forks, Gallatin County, MT, 6-11-2015, and in Rocky Mountain National Park, Larimer County, CO, 7-10-2019 (SRTurner).