Flower:

Elongating racemes with a rounded cluster at the end of the stem and maturing seed capsules along the stem below. The bright yellow flowers are about 1/3 inch across, the four petals are oval to round, broad at the tip with a narrow tapered base on a short stalk. Behind the flower are 4 narrow yellow sepals. The airy spray of blooming racemes typically cascades from its own weight.

Leaves and stems:

Leaves are variable. Lower leaves are up to 10 inches long and 4 inches wide, with a broad rounded lobe at the tip with several deep lobes towards the leaf stalk, the edges coarsely toothed. Leaves become stalkless, smaller, few-lobed to narrow, lance-like and unlobed above into the flowering branches. Leaf color is typically green but can have purplish markings and hues.

Early basal leaves and lower stem can be smooth but are typically rough with sparse bristly hairs on upper and lower surfaces, the stems often with a waxy bloom on the surface. The main stem is unbranched in the lower plant but axillary branches proliferate in the upper plant.

Fruit:

Fruit is a smooth pod, about ½ inch long with a short beak at the tip. Pods are erect, holding close to the stem.

Each pod holds an average of four seeds which can be dark brown to black with a rough textured surface.

Notes:

Black Mustard has been cultivated for thousands of years and is thought to be the mustard seed referred to in a parable by the biblical Jesus. It has fallen out of favor for varieties of Indian mustard (Brassica juncea) that produce more mechanically harvestable seed. It is a common weed of waste places and arid grasslands throughout the world. It is likely under reported in Minnesota.