Brassica nigra (Black Mustard)

Plant Info
Also known as:
Family:Brassicaceae (Mustard)
Life cycle:annual
  • Weedy
Habitat:sun; fields, waste areas, roadsides, disturbed soil
Bloom season:June - August
Plant height:2 to 8 feet
Wetland Indicator Status:none
MN county distribution (click map to enlarge):Minnesota county distribution map
National distribution (click map to enlarge):National distribution map

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Detailed Information

Flower: Flower shape: 4-petals Cluster type: raceme Cluster type: round

[photo of flowers] 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: Leaf attachment: alternate Leaf attachment: basal Leaf type: lobed Leaf type: simple

[photo of leaves] 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.

[photo of early rosette] 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 type: capsule/pod

[photo of 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.

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


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.

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More photos

Photos by K. Chayka taken in Ramsey County. Photos courtesy Peter M. Dziuk taken in Ramsey and Hennepin counties.


Have you seen this plant in Minnesota, or have any other comments about it?

Posted by: Vickie - Apple Valley
on: 2013-05-20 19:54:07

2nd year this has appeared in my wooded area. Wasn't sure if it was Wintercress.

Posted by: Dave - maple grove
on: 2016-07-03 23:55:35

Found in a new flower garden planted late last summer. Cone flowers, daffodils and hostas were planted. Came back from Florida and found this plant was 6 feet tall and in full bloom. Found several smaller plants in another flower bed a short distance away. Came in with the new plants or the mulch is my best guess.

Posted by: Wanda Martens - Mound
on: 2018-08-04 12:22:08

Found growing for first time in my front yard along with sunflowers, asters, milkweed etc. July 2018. Don't see anywhere in neighborhood. Assuming birds brought into yard.

Posted by: Gary - Carlton County
on: 2018-10-18 16:52:31

This plant showed years ago at my place in some poorly prepared compost from another part of the county. It is still here but only grows where the soil has been disturbed such as in gardens.

Posted by: Deborah A. Burt - Minneapolis
on: 2021-05-24 19:43:36

Showed up on my boulevard spring 2021 after the city removed a stump and placed black fill - full of weeds.

Posted by: JON NICHOLSON - New Hartford Twp., Winona County
on: 2022-08-14 12:55:43

I may have this, but Picture This identifies it as Brassica juncea (mentioned above in the "Notes". I think my plants may be juncea. The most notable thing about these plants is that the flowers are sweetly aromatic. Could that distinguish between nigra and juncea? I don't seem to be able to find any references to this sweet, perfumy aroma.

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