Flowers in long narrow spikes, yellowish green. Dark green wavy edged leaves.
Common names include dyer’s rocket, dyer’s weed, weld, woold, and yellow weed. this species was the most widely used source of the natural dye known as weld. The plant is rich in luteolin, a flavonoid which produces a bright yellow dye. The yellow could be mixed with the blue from woad (Isatis tinctoria) to produce greens.
It prefers waste places. Good weld for dye must have flowers of a yellow or greenish color, and abound in leaves; that which is small, thin-stemmed, and yellow is better than that which is large, thick-stemmed, and green; that which grows on dry, sandy soils is better than that produced on rich and moist soils.