Dyers' Greenweed, Dyers' Broom, Genista, a yellow dye plant that grows abundantly around Europe and the Mediterenean. From fresh yellows to goldens, and greens using ferrous sulfate. Genista has a good lightfastness, and was used a lot in the South of France in the dye houses.
Dye at around 30% wof.
Adding 1% of calcium carbonate to the dye bath will give clearer yellows.