Descurainia pinnata (Walter) Britton

Tansy Mustard

© SRTurner

Family - Brassicaceae

Habit - Annual or biennial forb.

Stem - Erect, 25-50 cm long.

	Stem.
© DETenaglia

Leaves - Alternate, pinnately compound, short petiolate or sessile. Blades 1-10 cm long, 2 or 3 times pinnately dissected, the leaflets toothed and oblanceolate to linear, the upper leaves progressively reduced and less divided.

	Stem and leaves.
© SRTurner

	Leaf.
© SRTurner

Inflorescences - Racemes or less commonly panicles, the flowers often not subtended by bracts.

	Inflorescence.
© SRTurner

Flowers - Sepals 4, lanceolate to ovate, ascending to erect, 1-2 mm long. Petals 4, 1.0-3.5 mm long, pale yellow. Styles absent or less than 0.5 mm long.

	Flowers.
© SRTurner

Fruits - Club-shaped or oblong, 5-10 mm long, 1-2 mm wide, blunt at the tip, the valves with 1 midnerve. Styles 0.1-0.2 mm. Seeds 10-40 per fruit, at least in part in 2 rows in each locule.

	Fruits.
© SRTurner

Flowering - March - July.

Habitat - Forest openings, streambanks, bluffs, glades, prairies, railroads, fields, open disturbed areas.

Origin - Native to the U.S.

Lookalikes - D. sophia.

Other info. - This native mustard is common throughout Missouri, and also across the western 2/3 of the continental U.S. It is easily recognized by its small yellow flowers arranged in the mustard pattern, and its highly dissected foliage. The appearance is similar to the introduced flixweed, Descurainia sophia, but that species has much longer, narrower fruits.

Descurainia pinnata has been subdivided into several infraspecific forms, two of which have been collected in Missouri. The ssp. brachycarpa, which is by far the most common, has glandular hairs on the stems and leaves. This is the form pictured above. In contrast, ssp. pinnata has stems and leaves pubescent with branched, nonglandular hairs.

Photographs taken at Hickory Canyons Natural Area, Ste. Genevieve County, MO, 5-1-2010, near St. Albans, Franklin County, MO, 4-18-2011 and 4-1-2012, Weldon Spring Conservation Area, St. Charles County, MO, 4-6-2012 (SRTurner).