Black Mustard is an erect annual plant growing on stiff stems to 8 feet high, sometimes with wide branching near the top. Upper stems are usually smooth while the lower stem may have some hair near the base.
The leaves vary from bottom to top. Lower leaves are pinnatifid in the shape of lyre or simple deeply lobed. The terminal lobe will be much larger. These can be quite large, up to 10 inches long and they are on long stiff stalks. Leaves in the inflorescence are usually not stalked, more elliptic to lanceolate in shape, like the lower leaves but reduced and less lobed and the margins may be toothed.
The inflorescence consists of terminal erect racemes that are rounded and the inflorescence can get quite long on large plants - up to 2 feet. They elongate as the flowers open from bottom to top, while seed pods form from the earlier flowers.
The flowers are 4-parted, 1/4 to 1/3 inch wide with 4 (usually) yellow petals that are ovate with rounded tips and a clawed base; 4 (usually) green to yellow, long and narrow sepals, six stamens with yellow anthers, grouped into pairs, and a pistil with a single style that has a blunt tip.
Seed: Mature flowers produce a 2-valved slender linear 4-sided seed pod (called a 'silique') with a slender beak. The pod is about 2/3 inch long on a 1/3 inch stalk. The pod is held appressed to the stalk of the raceme (not spreading) and usually contains 5 to 7 dark brown seeds, 1 to 1.5 mm long. These are dispersed when the pod splits open along the lines of the 2 valves.
Habitat: Black Mustard has a taproot but is an annual and re-seeds itself. On good soil in full sun with moist conditions the plant reaches its maximum potential. In poorer conditions it may be much shorter. It will be found along ditches and other waste places where it is undisturbed. If spreads into large stands if not disturbed.
Names: The genus Brassica, is the Latin name for cabbage, which is in this genus. The species, nigra is Latin for 'black' referring to the seed color. A synonym name is Sinapis nigra L. The author names for the plant classification are: First to classify was - '(L.)' - which is for Carl Linnaeus (1707-1778), Swedish botanist and the developer of the binomial nomenclature of modern taxonomy. His work was ameded by ‘W.D.J.Koch’ which is for Wilhelm Daniel Joseph Koch (1771-1849), German botanist, Professor of Botany at Erlangen, author of several publications on European plants, who furthered the work of Linnaeus on this plant.
Comparisons: Several plants may be confused with Black Mustard, particularly Charlock Mustard, Sinapis arvensis L. but there the seed pods are knotty or wavy and not appressed to the raceme stalk. Black Mustard is quite tall compared to others.
Above: 1st photo - The inflorescence is a terminal raceme and others rising from the leaf axils. 2nd photo - The yellow petals have tips rounded to a blunt point.
Below: 1st photo - Detail of the yellow-green sepals, the clawed base of the petals, stamens and pistil. 2nd photo - Seed pods forming below and flowers above open.
Below: The terminal lobe of the leaf is much larger than the other lobes. Margins have coarse teeth.
Below: Comparison of the shapes of various stem leaves.
Below: 1st photo - A plant with many flower racemes. 2nd photo - Stems are stiff, stout with slight angles and fine hair near the base. 3rd photo - The seed pods (siliques) are appressed to the stem.
Below: 1st photo - A large 7 foot plant. 2nd photo - Each mature seed pod holds 5 to 7 seeds which turn dark brown at maturity. While the pod is of two valves, note the obvious 4-angles to the pod, with the dry stalk at one end and the beak at the other.
Notes: Black Mustard is native to Eurasia and has become naturalized in North America. The plant is found throughout the U.S. and southern Canada and is most abundant near the West Coast. It has been recorded in a dozen Minnesota counties including Hennepin where the plants pictured above were found.
Uses: Seeds of Black Mustard are used in condiments and for the oil contained in the seeds. The plant is cultivated for that purpose. The plant has an ancient history being recorded by the Greeks and Romans. The seeds themselves do not have an odor. Many members of the genus Brassica have all had some uses as food crops.
References: Plant characteristics are generally from sources 1A, 32, W2, W3, W7 & W8 plus others as specifically applied. Distribution principally from W1, W2 and 28C. Planting history generally from 1, 4 & 4a. Other sources by specific reference. See Reference List for details.
Friends of the Wild Flower Garden, Inc. Text and photos are by G. D. Bebeau unless otherwise credited. "www.friendsofthewildflowergarden.org"