Flower:

Stalked flowers in rounded to cylindrical clusters 1 to 1½ inches across at the tips of branching stems and arising from leaf axils. Flowers are ¼ to 1/3 inch across with 4 yellow petals, 6 yellow stamens and a stout style.

4 yellow to yellow-green sepals, about 1/8 inch long, surround the base of the flower. Clusters elongate as the plant matures, with flowers blooming at the tip and fruit forming along the stem below. 

Leaves and stems:

Leaves are basal and alternate. Near the base of the plant they are deeply lobed with a large rounded lobe at the tip and 1 to 4 pairs of small oblong-elliptic lobes widely spaced on the stalk. Basal leaves are up to 2½ inches long and up to 1 inch wide, the stalk ½ to 3 inches long or sometimes longer. Lobe edges can be somewhat wavy and shallowly lobed or with a few coarse teeth.

Leaves become smaller as they ascend the stem and typically have a pair of largish lobes (auricles) at the base of the stalk that clasp the stem and have scattered hairs around the edge. Uppermost leaves may be less finely divided with little or no stalk. Stems are single or multiple from the base, branched in the upper plant, ridged or angled, purplish or green with purple streaks or stripes, and hairless.

Fruit:

Fruits are slender, erect to ascending, green pods up to 1½ inches long that are straight to slightly curved. The pods hold numerous tiny, brown, oval to oblong seeds.

Notes:

American Yellow Rocket is a circumpolar species native to North America and Asia, and is more common in the western states and into Canada. In Minnesota it is primarily found in the Arrowhead region near the rocky shore of Lake Superior. It is far less common here than the look-alike, non-native Garden Yellow Rocket (Barbarea vulgaris). While there are small differences in flower size, leaf shape and fruit arrangement, the most obvious difference is the fringe of sparse hairs on at least some leaf auricles, where Garden Yellow Rocket is completely hairless.