Mustasa is widely distributed in the settled areas of the Philippines, in towns, near houses, etc., planted and spontaneous. It was certainly introduced from the Asia, and is now pantropic in distribution, occurring also in some temperate regions.
The plant is an erect, branched, smooth annual, 0.4 to 1 meter in height. The leaves are oblong-obovate to oblong lanleocate, 5 to 15 centimeters long, or in some cultivated forms much larger, thin, irregularly toothed or subentire, the lower ones sometimes being lobed or pinnatifid. The flowers are yellow and 6 to 8 millimeters long. The pod is ascending, linear-lanceolate, 1.5 to 3 centimeters long, and somewhat contracted between the seeds, and the beak is seedless.
The leaves are eaten in the Philippines as a green leafy vegetable, either fresh or pickled in brine. Marañon shows that the leaves are excellent sources of calcium, phosphorus and iron. Hermano and Sepulveda claim that they are a good source of vitamin B.