Weld (Reseda luteola)

This tall biennial with its yellow to green spikes has been used for thousands of years as a dye, producing a bright yellow.  This was mixed with woad (Isatis tinctoria, a blue dye) to make greens, such as Lincoln Green.  It will grow in moist areas but prefers dry, sandy soils, which also gives the plant a richer yellow when dried for dyeing.