Descurainia pinnata (Tansy Mustard)
|Also known as:||Pinnate Tansy Mustard, Western Tansy Mustard|
|Life cycle:||annual, biennial|
|Habitat:||sun; dry, sandy or rocky soil; roadsides, railroads, plains, prairies, outcrops, bluffs, gravel pits|
|Bloom season:||May - July|
|Plant height:||8 to 24 inches|
|Wetland Indicator Status:||none|
|MN county distribution (click map to enlarge):|
|National distribution (click map to enlarge):|
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Elongating racemes 2 to 12 inches long of stalked flowers at the tips of branching stems, with a small, flattish cluster of flowers blooming at the tip and fruit forming below. Flowers are up to 1/8 inch across with 4 spreading to ascending, spoon-shaped, yellow petals alternating with 4 egg-shaped yellow sepals that are slightly shorter than the petals. In the center is a stout style surrounded by 6 yellow stamens about as long as the petals. Stalks are very slender, erect to ascending, and up to about 2/3 inch long. Sepals and flower stalks are variably covered in glandular hairs, sometimes non-glandular hairs.
Leaves and stems:
Leaves are once or twice pinnately compound, broadly lance-oblong in outline, basal and the lowest leaves stalked, up to 6 inches long and 2½ inches wide, feathery with numerous, deeply to shallowly lobed divisions, becoming smaller, stalkless, and less lobed as they ascend the stem. Surfaces and stalks are variably covered in glandular hairs, especially the leaf underside.
Flower stalks become ascending to widely spreading in fruit, usually forming an angle 60 degrees or less with the stem. Fruit is a straight to slightly curved, spreading to ascending pod called a silique, up to about ½ inch long, shorter than the stalk, slender but distinctly plumper than the stalk, and somewhat broader at the tip than the base (inconspicuously club shaped). Inside are 2 rows of 10 to 20 seeds each, with visible constrictions between the seeds.
Tansy Mustard is most often found in sandy or gravelly areas with soil disturbance, such as roadsides and along railroads, but can occur in less disturbed habitat as well. Very similar is the non-native Herb Sophia (Descurainia sophia), which is most easily distinguished by the lack of glandular hairs and longer, more slender fruit. Also similar is Richardson's Tansy Mustard (D. incana), a species not seen in Minnesota since 1936, which is hairy but not glandular, has once pinnately lobed leaves, and mostly erect fruits, appressed to the stem. Depending on the reference, there are between 4 and 10 subspecies of D. pinnata; of the 4 most commonly recognized, 3 are limited to the southwestern or southeastern US, with subsp. brachycarpa widespread in North America, including Minnesota, and described above. Distinguishing characteristics with the other 3 subspecies are overall hairiness, glandular or not, whether or not stems branch at the base, and the angle of the fruit stalk relative to the stem.
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Where to buy native seed and plants ↓
- Tansy Mustard plant
- unbranched Tansy Mustard in sand prairie habitat
- Tansy Mustard in rock outcrop habitat
- roadside Tansy Mustard
- emerging in spring
- more flowers, with a pollinator
Photos courtesy Peter M. Dziuk taken in Dakota and Renville counties.
Have you seen this plant in Minnesota, or have any other comments about it?