Brassica nigra
“The plant is a tyrant and a nuisance, – the terror of the farmer;
it takes riotous possession of a whole field in a season;
once in, never out;
for one plant this year, a million next;
but it is impossible to wish that the land were freed of it.
Its gold is as distinct a value to the eye as the nugget gold is in the pocket.”
Helen Hunt Jackson (Ramona,1884)
Sinapis nigra
Black mustard (Brassica nigra) is a tall, many branched, often weedy-looking annual plant. It often reaches six feet and may occasionally double that height. Lower leaves are supported by petioles. Lower leaves are large, to ten inches (25 cm) long and lobed or divided into three or five pinnate lobes of which the terminal lobe is distinctly larger than the others. Higher on the stem, leaves become smaller and less divided with toothed margins, and the petioles become smaller or absent. Stems and leaves, especially the lower leaves may have stiff white hairs on the under surface especially along the veins. The upper surface is generally smooth. Plants die in summer, leaving the skeletal stems standing until battered down by winter winds and rain. This dried vegetation is flammable.183
Bright yellow flowers occur in small clusters on small stems at the ends of the main branches. All together, several mustard plants can produce a brilliant display. Open flowers surround the base of each rounded cluster, with buds of decreasing sizes developing in the middle. Symmetrical flowers are about 1/2 inch (1 to 1.6 cm) across with four sepals and four petals. Petals are paddle-shaped, flaring outward from an erect claw. There are six stamens, two shorter than the others; anthers are hot-dog-bun shaped, and both anthers and pollen are light yellow. There is one pistil, about the same length as the stamens. The ovary is superior; the style is reduced to a short beak and there is a small capitate stigma. As flowering progresses, the flower stalk lengthens with new flowers on top and maturing fruit below, appressed to the leafless stem.
The elongate fruit are dry, two-chambered pods an inch (2.5 cm) or less in length, ending in a short, seedless beak that is often separated from the pod by a constriction above the uppermost seed. On maturity the pods split into two valves releasing seeds that are attached to a central membrane. Tiny rounded seeds are dark reddish or grayish with reticulated surfaces.
Black mustard is thought to be native to the middle-East,353 southern Europe or southern Asia41 where it has been cultivated for thousand of years. Since then, uses of mustard have evolved and the plants have spread globally. Black mustard is currently found throughout Canada and the United States where it is considered a noxious weed in 44 of the 48 lower states.
In California, black mustard is widespread, and plants have been reported from many vegetation types up to 7000 feet (2100 m). It is most common near the coast and associated with coastal sage scrub, especially in disturbed areas such as roadsides, past or presently cultivated areas and areas cleared for fire.
In the reserve it is ubiquitous along the trails and the dike. In spite of eradication efforts, black mustard still marks areas of old farms and homesteads such as at Santa Carina and on Stonebridge Mesa.
Black mustard is dicot angiosperm in the mustard family (Brassicaceae), a family of major economic importance that has very broad distribution. It contains many well-known species and cultivars including common vegetable crops such as cabbage, cauliflower, broccoli, turnips, water cress and radish, and ornamentals such as sweet alyssum and stock. Rapeseed, the source of canola oil, is in the mustard family. There are also invasive weeds such as black mustard, wild radish and sea rocket.
Members of the mustard family are characterized by four petals in a cross shape (from which came the former family name Cruciferae, or cross-bearing); and by six stamens, four long and two short. Mustard seed pods come in different shapes. When mature, they split open from both sides, exposing the seeds on a central membrane.
Sixteen species in the mustard family have been reported from the Reserve.48 Eight of these are non-native weeds, including black and field mustard (Brassica rapa), wild radish (Raphanus sativus), sea rocket (Cakile maritima) and stock (Matthiola incana). Others include lovely spring natives such as milkmaids (Cardamine californica) and western wallflowers (Erysimum captatum).
Sinapis nigra
Black mustard flourishes in disturbed areas59 and rarely invades established native vegetation.174,353 Re-occupation of a black mustard stand by native plants is slow. Several factors have been implicated in maintaining this strong spatial dominance of black mustard.
Like the related wild radish, black mustard lacks the symbiotic, or mutualistic, relationship with soil fungi – a “mycorrhizal association”161 – that characterizes many of our native plants and facilitates their uptake of water and nutrients from the soil.41,153,155 In the absence of the soil fungi, mycorrhizal plant growth is impeded.59,155 Because black mustard lacks this mycorrhizal dependence, the absence the mutualistic partners does not restrict its growth, giving it a competitive advantage over native plants in areas where the soil has been disturbed.
In addition, black mustard produces allelopathic compounds that may inhibit the germination of surrounding plants.183,355Compounds leaching from dead stalks and leaves have been shown to reduce germination of non-native annual grasses in California grasslands and may also inhibit native plants.
Black mustard may also reduce the re-establishment of new native plants by shifting herbivory away from the mustard patch to other plants.356 The seeds of black mustard are too small for most seed-eating mammals. A stand of black mustard offers physical refuge to a variety of small mice and rabbits but mammals must forage elsewhere. The amount of seedling production of a native bunch grass, Stipa pulchra, is strongly dependent on the distance from a mustard patch, approaching zero at the edge of the patch and effectively eliminating the possibility that the bunch grass will recolonize the mustard habitat.
In spite of persistent eradication effort in the Reserve, black mustard returns each year – an ornery guest that refuses to take the hint.
Several species of mustard, including black mustard, have been cultivated for thousands of years. Egyptian Pharaohs put mustard seeds in their tombs to accompany them into the afterlife. Romans ground the seeds to flavor wine or vinegar and French monks mixed ground seeds with “must” (unfermented wine), giving rise to the name “mustard”.354 It has also been used medicinally for a wide variety of ailments from toothaches to frostbite prevention.41,354
Today, the greatest use of black mustard is for mustard seed, primarily ground and mixed with oil and vinegar to make table mustard. It was estimated that the global production of mustard seed (all species) in 2010 was over 59 million metric tons.353
A special relationship with mustard has developed among the wineries of California, where mustard is used as a cover crop and to provide control of soil nematodes. There it has become a tourist-attracting icon, giving the vineyards their brilliant, magical, spring color.357
It is said that the early Franciscan padres scattered mustard seeds along El Camino Real making a golden trail between the missions of Alta California that would guide weary travelers to shelter. It is not known whether this often-repeated story is true, but it makes a lovely image – in spite of the disastrous ecological consequences.
