Ethiopian Mustard

Brassica carinata is a tall annual, often 1.5 to 2 meters, with thick stems, bluish-green waxy leaves and clusters of bright yellow flowers. The pods are slender and keeled, holding many tiny round seeds that are dark brown to blackish and roughly 1.5 to 2 millimeters across. Seeds are pungent when crushed, with a sharp, hot mustard flavor and an oily richness. In Ethiopia the leaves are cooked as greens and the seeds are ground as a condiment, while commercial growers press them for oil. Compared with other mustards the plant tolerates heat and drought relatively well, which makes it attractive for dry regions.

Brassica carinata is an allotetraploid species that arose from natural hybridization between black mustard (Brassica nigra) and cabbage-type Brassica oleracea, and it is thought to have originated in the Ethiopian highlands and nearby areas of northeastern Africa. It has been cultivated there for a very long time and is still grown as a local vegetable and oilseed. The species name carinata comes from Latin carina, meaning keel, which refers to the keeled shape of the seed pod. The common names Abyssinian mustard and Abyssinian cabbage refer to Abyssinia, the old name of Ethiopia.

Ethiopian mustard has deep roots in the agriculture of the Ethiopian highlands, where farmers have grown it for greens and oil for centuries alongside crops such as teff, barley and enset. Locally the leaves, known by names such as gomenzer, are cooked with spices and eaten with injera, while the seeds are ground for sauces and the oil is used in cooking and lighting. It also spread to parts of East Africa, and to Mediterranean and Asian regions on a smaller scale.

Outside Africa the plant was long a scientific curiosity: Nagaharu U's 1935 work on the relationships among cultivated Brassica species, known as the triangle of U, helped explain how carinata arose from two parent species. In the late twentieth and twenty-first centuries, interest grew in carinata as a non-food oilseed because its oil is rich in erucic acid, which suits industrial uses, and because the plant performs better than canola in hot, dry conditions. Breeders in Canada, the United States, Europe, Australia and South America have developed varieties for biofuel feedstock, including aviation fuel, and the crop is also being studied for its meal as animal feed and for green manure.

In Ethiopia the cooked leaves are a common vegetable, and ground seeds are used as a hot condiment or mixed into spice pastes. The seed oil is traditionally used for cooking in some areas and for lamp fuel. Commercial varieties are grown for industrial oil used in biodiesel, jet fuel feedstock, lubricants and bioplastics. The leftover meal is used as animal feed after processing to reduce glucosinolates. In some regions the plant is used as a cover crop or biofumigant, because its residues can help suppress soil pests. Edible varieties with low erucic acid are under development.

Like other mustard greens, Ethiopian mustard leaves supply vitamins A, C and K, folate, calcium and fiber. Seeds and meal contain glucosinolates, sulfur compounds that give the pungent taste and have been studied for potential protective effects, but in high amounts they can affect the thyroid. Traditional oils high in erucic acid have been linked in animal studies to heart problems, so industrial varieties are not intended for food oil. Human studies on the plant are limited.