Invasive Plant Profile: Black Mustard

Black Mustard (Brassica nigra). Photo courtesy of Keir Morse.

A variety of lush greenery and brightly colored flowers can be found while hiking through the Irvine Ranch Natural Landmarks, but not all of the blooms we see are native to the land. Brassica nigra, or the black mustard, is an invasive plant that can reach up to six feet tall in a single growing season. Its bright yellow, four-petaled flowers bloom from April to July.

This winter annual plant is native to tropical regions of North Africa, temperate regions of Europe, and parts of Asia. In California, this invasive weed is common in coastal areas at lower elevations. In disturbed areas such as roadsides, fields, and grasslands this plant forms single-species stands.

Black mustard is cultivated for its black or dark brown seeds, which are commonly used as a spice. Like other mustard species, it produces many seeds each season, grows profusely and produces allelopathic chemicals that prevent the germination of native plants. Black mustard leaves behind dry fuel at the end of each growing season and once it spreads, fire frequency increases in chaparral and coastal sage scrub, converting these habitats to annual grassland.

Irvine Ranch Conservancy and its partners, OC Parks, City of Irvine and the City of Newport Beach, work diligently to help stop the spread of black mustard on the Landmarks. Volunteers interested in helping with the removal of black mustard and other invasive plants can sign-up for stewardship activities on LetsGoOutside.org.  

For more information about the Landmarks, visit IRConservancy.org or follow the Landmarks on Facebook, Instagram and Twitter.

---