Brassica juncea, commonly known as brown mustard or Indian mustard, is a fast-growing annual herb native to central Asia. It is a member of the Brassicaceae family and has been cultivated for centuries across Asia and Europe for its leaves, seeds, and oil. The plant is characterized by its lyrate-pinnatifid leaves, yellow flowers, and elongated seed pods (siliques), typically reaching 3–12 feet in height. It is highly valued as a leafy vegetable, a source of cooking oil (mustard oil), a spice (mustard seed), and as a cover crop in agriculture due to its soil-improving properties.

Despite its usefulness, Brassica juncea poses several ecological risks in regions where it is not native. It has become widely naturalized around the world, including in Hawaiʻi, where it can escape cultivation and invade disturbed areas, roadsides, and natural ecosystems. It is considered an environmental weed that can outcompete native plants. The plant is highly adaptable, tolerates a wide range of soils and climates, produces many seeds, and can hybridize with related species. While not toxic to humans, its seeds can be harmful to livestock if consumed in large quantities. Care should be taken to prevent its spread into natural areas.