Weld is the dried plant Reseda luteola, a species of wild mignonette, formerly largely cultivated in Europe.
Various, Encyclopaedia Britannica, 11th Edit...(2010)
Weld, Reseda luteola, is an annual plant growing in waste places.
Mairet, Ethel M., Vegetable Dyes—Being a Book of Reci...(2010)