Flower:

Flowers are in rounded clusters at the tip of branching stems at the top of the plant. The blooming stems elongate as the plant matures, with blooms just at the top. Individual flowers are yellow, ¼ to 1/3 inch across, with 4 rounded petals and 4 yellow-tipped stamens.

Leaves and stem:

Leaves are up to 4 inches long and ¾ inch wide, toothless or with a few small teeth, tapering to a point at each end, and little or no leaf stem. 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 main stem is 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. The pod angles up at its stem joint.

Notes:

There are a number of yellow mustards that grow in Minnesota. Ways to distinguish them are the shape of the leaves and the size of the flowers. Wormseed Wallflower has flowers 1/3 inch across or less, leaves that are not divided or lobed, and a distinctly ribbed stem.