woad (isatis tinctoria) - a hardy biennial/perennial (depending on zone) dye plant in the brassica family. grows up to 3ft tall with small yellow flower clusters. can grow in most soil, full sun or part shade. used in TCM for a wide array of medicinal attributes. yields a blue dye that can also be used as a wood preservative. native to central-western asia. hardiness zone 6-9