Brassicaceae: Descurainia pinnata
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Family Name
Brassicaceae
Common Name
Western tansymustard, stingweed
Description
Descurainia pinnata is an annual or short-lived perennial herbaceous plant growing from a fibrous root system, typically 10 to 60 centimeters tall, with slender, often branched stems, often covered with soft, spreading hairs. Leaves are alternate, pinnately divided or deeply lobed into thread-like, narrow segments with short and inconspicuous petioles.; basal leaves are larger, up to 10 cm long, deeply divided with linear lobes 1–3 mm wide, while upper leaves are smaller and less divided, usually 2 to 6 cm long. Flowers are small, yellow, arranged in loose racemes blooming from spring through late summer (April–August). Each flower is about 3 to 5 millimeters in diameter, with four yellow petals roughly 1.5 to 3 millimeters long and 0.7 to 1.5 millimeters wide, and four green sepals approximately 2 to 3 millimeters long and 0.5 to 1 millimeter wide. There are six stamens per flower, four longer and two shorter (tetradynamous), inserted around the superior ovary. The pistil consists of a single ovary with a slender style and a capitate stigma. The fruit is a slender, curved silique about 15 to 40 millimeters long and 1 to 2 millimeters wide, containing numerous small seeds. Fruits mature from mid to late summer. Western tansymustard is native to South Dakota and grows in disturbed soils, dry prairies, roadsides, sandy or gravelly sites, and open woodlands statewide.
Horticulture Notes
Seed Collection: Seeds are mature when siliques turn brown and dry; seeds can be collected by shaking dry plants in late summer.
Germination: Seeds germinate readily without dormancy; best sown in spring in well-drained soils.
Vegetative Propagation: Not propagated vegetatively; reproduces via seed.
Soils: Prefers dry to moderately moist, well-drained soils, including sandy and gravelly substrates.
Light: Thrives in full sun.
Water: Drought-tolerant once established; requires minimal supplemental water.
Additional Notes
Western tansymustard is native to South Dakota, is known for its resilience in disturbed and dry habitats and provides early-season nectar and pollen for native bees and butterflies. It is sometimes included in reclamation or restoration seed mixes for disturbed and arid sites.