Plants of Southern California: Analysis Pages: Mustard (Brassica nigra and Hirschfeldia incana): How To Tell The Difference
Many people are confused about the difference between black mustard, Brassica nigra, and shortpod mustard, Hirschfeldia incana (older name was Brassical geniculata), both non-natives and quite invasive, displacing native plants. These are both somewhat variable plants, so it is indeed difficult to distinguish them at times. However, the vast majority of the time, it is very easy to distinguish them using the following characteristics:
- Height. The general rule is that if you are looking up or level to the top of the plant, it is black mustard. If you are looking down to the top of the plant, it is shortpod mustard. See pix of dead black mustard stalks from Spring 2001 towering over Tom's 5' 2" wife at Crystal Cove State Park in April 2002. (April 2002 was the severe-drought year; essentially no annuals germinated that year.)
In very low rainfall years, black mustard won't achieve its usual height. But even then, the difference in height is clear. See pix of a black mustard plant placed next to a shortpod mustard plant from Laurel Canyon, Orange County, on 9 May 2004, when the rainfall was only half-normal. The black mustard was growing just tens of feet away from the shortpod mustard, and it still achieved a height of ~5-6 feet, compared to the ~3 foot height of the shortpod mustard. Tom pulled the black mustard out of the ground easily (see below) to place it next to the shortpod mustard. The difference in height is readily apparent.
The great height of black mustard is even mentioned in the Bible.
- Leaves. Shortpod mustard has its leaves mostly hugging the ground in a basal rosette, and the leaves are usually lobed. Black mustard has virtually no leaves hugging the ground; most of its leaves are along the stem and are mostly unlobed. The comparison pix from Laurel Canyon shows how clear the difference is. Note the cauline leaf on the black mustard stem that is above the entire shortpod mustard plant. A blowup of the lower portion of the stem shows that the black mustard stem is naked at flowering time, without any lower leaves at all, in dramatic contrast to the leafy rosette that is still present in shortpod mustard in bloom.
- Plant duration. Black mustard is an annual, and hence an individual plant will die at the end of each growing season. If the ground is not too hard, it can be pulled out of the ground easily, since annuals do not have extensive root systems. Shortpod mustard is a perennial, although it can flower the first year from seed. Individual plants will rarely die at the end of each year, but instead will persist, with the root system getting stronger and stronger. Except for first-year plants, it cannot be easily pulled from the ground. Instead, the stems will break above the roots, allowing the plant to grow again the next year.
- Location. Black mustard only grows near the coast at fairly low elevations, where it is usually the most common mustard. Shortpod mustard grows everywhere up to at least 6500 feet, and is the most common mustard, or only one, above elevations of ~500-1000 feet.
Out of our 75 trail plant lists we've done in Southern California, black mustard is only found on six, and on only four trails in abundance: Santa Monica Mountains: Lower Hondo Canyon; Orange County: Crystal Cove State Park: Reef Point, Green Route; Laurel Canyon. All of these trails are within five miles of the coast, and are at low elevation. In contrast, shortpod mustard is found on 40 trails, essentially on every trail below 7000 feet elevation, including all of the ones where black mustard is found.
- Stem and leaf hairiness. Shortpod mustard usually has a significant number of short hairs along its stem; black mustard has few to none. The hairs of shortpod mustard are dense, soft and white, and are most noticeable on the leaves. The scattered hairs on black mustard are stiff and bristly.
- Bud hairiness. Jon Rebman supplied the tip that shortpod mustard always has at least a few hairs on its buds, whereas black mustard has none.
There is a difference in the flower color, but it is impossible to use in the field unless you have both plants side by side, as in this pix from Laurel Canyon. The shortpod mustard flower, on the right, is paler yellow than the black mustard flower on the left.
I have learned that some hikers like to munch on the flowers of "black mustard", so it is of interest to know whether both species are equally edible. Fortunately, they both are. From the web:
Black mustard: "The seeds of this plant and the leaves are both edible. There are many nutritional properties of merit in Brassica nigra; for example vitamin A, vitamin B complex, vitamin C and calcium can all be found. See the full list of nutritional values for more. Black mustard is typically used as a flavoring. This plant is most frequently used fresh." (Source: Crescent Bloom)
Mustard seed is commonly ground into a powder and used as a food flavouring and relish [4, 5, 17, 27, 34]. This is the black mustard of commerce, it is widely used as a food relish and as an ingredient of curry". Known Hazards: When eaten in large quantities, the seed and pods have sometimes proved toxic to grazing animals ." Source: GardenBed.com
Shortpod mustard: "Edible Uses: Leaves; Seed. The young plant is eaten with oil and lemon juice in parts of Greece . The leaves of young plants are eaten raw [61, 177]. Seeds - raw or cooked . They can be ground into powder then mixed with water and eaten ." Source: Plants For A Future
One final comment: don't believe what you read in the floras, like the Jepson Manual, about the sizes of these plants. The heights and leaf lengths are often much, much larger than the sizes given in the floras. As a budding botanist, one of Tom's first uses of his newly-purchased Flora of Southern California by Munz was to try to figure out if the mustard in his back yard was shortpod or black. He tried to use the leaf size to discriminate them, went to his unwatered back yard and measured a leaf size that was far greater than was reported in the flora for either species.
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Last update: 17 August 2011