The spicy mustard plant that also pulls heavy metals out of soil
Brown mustard seasons dishes from Punjab to Okinawa and gives its name to a condiment spicier than the yellow kind. The same plant also soaks up lead and cadmium from contaminated ground, storing the metals in its own cells until it is harvested and hauled away, a cheaper clean-up than digging out the dirt.
Brassica juncea goes by a long list of names, among them mustard greens, Indian mustard, Chinese mustard and leaf mustard. Its cultivars fall into four subgroups, and its leaves, stems and seeds are all edible. It is grown both for greens and for mustard oil, and it bites harder than its milder cousins kale, broccoli and collards, so cooks often blend them.
Its culinary range is enormous. In northern India and Pakistan the greens become sarson da saag. A thick-stemmed variety is pickled into Nepali achar and the Chinese zha cai, while in Japan the leaf called takana is pickled and tucked into rice balls. Gorkha communities in Darjeeling and Sikkim cook it with pork, and in Nepal goat meat is pressure-cooked with the greens and dried chillies. On Taiwanese New Year's Eve the leaves appear at reunion dinners as a symbol of long life.
The oil has a complicated status. Because it may contain erucic acid, mustard oil cannot be imported into the United States as a cooking oil, yet the essential oil is generally recognised as safe there. Russia takes the opposite view in practice: it is the country's main mustard crop, used for canning, baking and margarine, and most Russian table mustard comes from it.
Farmers have tested it as a weed suppressor. Sown in autumn and tilled in during spring, it cut weeds in later chile pepper crops by as much as 56%. But it suffers in cold, can boost root-knot nematodes and hosts a leafhopper that spreads viruses, so it has not caught on. The metal-scavenging trick has a bonus: covering polluted ground with plants also reduces erosion and the spread of contamination between sites.
Source: Brassica juncea
