Flower:

Elongating clusters of stalked flowers at the top of the plant and the ends of branching stems, with a small cluster of a few to several flowers blooming at the tip and fruit forming below. Flowers are pale yellow to nearly white, ¼ to 1/3 inch across, the 4 petals rounded, spatula shaped, narrowed at the base, the tip half widely spreading. In the center are 6 yellow stamens and a short style.

The 4 sepals are erect, narrowly lance-oblong with a blunt point at the tip, about half as long as the petals, green to reddish tinged, and sparsely covered in stiff, curved white hairs. Flower stalks are short but enlongating up to 3/8 inch in fruit, and similarly hairy.

Leaves and stems:

Leaves are deeply divided, oblong or widest near the tip (oblanceolate) in outline, pinnately lobed with 3 to 10 major lobes per side, the lobes mostly narrow, the edges shallowly lobed and rounded or angled at lobe tips, and the terminal lobe largest. Basal and lower leaves are 1 to 11 inches long, 1/3 to 4 inches wide, becoming smaller as they ascend the stem. Surfaces and leaf stalks are sparsely covered in stiff, curved, appressed white hairs. Stems are branched or not, erect to ascending, and sparsely to moderately covered in stiff, curved, appressed white hairs.

Fruit:

Fruit is a smooth, slender, 4-sided pod, ¾ to 1½ inches long with a short beak at the tip. Fruit stalks are ascending with the pods straight to slightly curved upward and seeds arranged in one row.

Seeds are reddish brown, 1 to 1.5 mm long, and have slight honeycomb texture.

Notes:

When looking at just the flowers, one might think all yellow mustards look alike, but Dog Mustard is distinguished from the others by its pale yellow flowers, narrow and erect sepals, deeply lobed leaves, ascending fruit, and the stiff hairs on sepals, leaves, stalks and stems. The leaf size can be quite variable, especially lower and basal leaves, and may be affected by moisture and other environmental conditions. Some populations we encountered had quite robust plants while others were small and spindly. The leaf shape and hairs will still be there. Dog Mustard is likely under-reported in Minnesota.