Flower:

Flowers are in rounded clusters at the top of the plant and the tip of stems arising from leaf axils in the upper plant. The blooming stems elongate as the plant matures, with blooms just at the top and fruit developing below. Individual flowers are yellow, from less than ¼ inch up to 1/3 inch across, with 4 rounded petals and 6 yellow-tipped stamens, 2 of which are shorter than the others.

Leaves and stem:

Leaves are up to 4 inches long and ¾ inch wide, spreading to ascending, narrowly lance-elliptic, toothless or with a few small teeth, tapering to a point or blunt at the tip, and little or no stalk. Surfaces are covered in minute star-shaped hairs. Attachment is alternate. Leaves become somewhat smaller as they ascend the stem; those near the flowers may be much smaller. There is also a basal rosette of leaves that withers away by the time seed starts forming. The stem is angled, ribbed and covered in very short hairs.

Fruit:

Fruit is a slender, straight 4-angled pod about 1 inch long containing a single row of seeds. Pods are spreading, ascending from the stalk, or nearly erect.

Notes:

There are a number of yellow mustards in Minnesota. Typical ways to distinguish them are the shape of the leaves, the size of the flowers, and the shape and arrangement of the fruits. Wormseed Wallflower has flowers 1/3 inch across or less, leaves that are not divided or lobed, and also has a distinctly ribbed stem. Of the 2 other yellow mustards with similar leaves—both of which are native, Western Wallflower (Erysimum asperum) has flowers ¾ to 1 inch across and fruits to 3 inches long; Small-flowered Wallflower (Erysimum inconspicuum) has flowers 1/8 inch or less.