Black mustard is a coarse annual weed, either branched or not.
The flowers very small, yellow, the 4 petals arranged like a cross, about ⅜ inch wide. Arranged in clusters at the tips of the plant stems.
Blooms April–November.
The leaves are on long petioles (leaf stems), highly variable, often irregularly lobed to the midrib, generally ovate, some with teeth.
The fruits are long seedpods (called siliques) that form at the bottoms of the flower clusters as flowering continues at the tops of the clusters.
Similar species: There are 4 species of Brassica recorded growing out of cultivation in Missouri. All originated as introduced crop plants. In addition to black mustard, there is brown, leaf, Indian, or Chinese mustard (Brassica juncea); rutabaga or rapeseed (the source of canola oil) (Brassica napus); and field mustard or turnip (Brassica rapa). Because of their many growth forms and hybrids, these can be hard to identify in the wild.
Height: to 5 feet.
Scattered statewide.
Habitat and Conservation
Grows in fields, waste places, roadsides, and other disturbed areas. Introduced; native to Eurasia.
Status
Nonnative, introduced plant. Native to Eurasia. Introduced as a crop plant.
Human Connections
Until it was recently replaced by brown mustard (Brassica juncea), black mustard was the chief source of seed used in making table mustard, a preparation that also contains extracts from another species, white mustard (Sinapis alba).
Seed extracts from these plants are also used medicinally and in the preparation of some scented soaps.
The genus Brassica includes many important agricultural plants, including broccoli, cabbage, kale, collards, cauliflower, and more. Some kinds are used medicinally or in pharmaceuticals. Many kinds of mustards have escaped from cultivation; all are immigrants with a great variety of leaf shapes.
This species has been cultivated in the Old World for thousands of years. It may be the species Jesus was thinking of when he told his “parable of the mustard seed” in the book of Matthew.
Ecosystem Connections
Although black mustard has escaped cultivation nearly throughout North America, it is not considered a serious invader because it is an annual, mainly grows only in disturbed soils, and does not threaten native habitats or displace native plants.
The familiar cabbage white butterfly was also imported to North America from Europe, apparently in a shipment of cabbage. Its larvae eat mustard plants and are serious crop pests. Our native white butterflies, including the falcate orangetip and checkered white, use mustards as host plants, too.
