1. Isatis tinctoria Linnaeus, Sp. Pl. 2: 670. 1753.
Dyers woad Dyers woad
Plants glaucous, usually glabrous, sometimes pubescent proximally. Stems (3-)4-10 (-15) dm. Basal leaves: petiole 0.5-5.5 cm; blade oblong or oblanceolate, (2.5-)5-15(-20) cm × (5-)15-35(-50) mm, base attenuate, margins entire, repand, or dentate, apex obtuse. Cauline leaves: blade usually oblong or lanceolate, rarely linear-oblong, base sagittate or auriculate, apex acute. Fruiting pedicels 5-10 mm. Flowers: sepals 1.5-2.8 × 1-1.5 mm, glabrous; petals 2.5-4 × 0.9-1.5 mm, base attenuate; filaments 1-2.5 mm; anthers 0.5-0.7 mm. Fruits black or dark brown, often broader distal to middle, (0.9-)1.1-2(-2.7) cm × 3-6(-10) mm, base cuneate, margins sometimes slightly constricted, apex usually subacute or rounded, rarely subemarginate; locule with distinct midvein, lateral veins inconspicuous, 3-6(-10) mm; apical wing 3.5-5(-7) mm wide. Seeds light brown, 2.3-3.5(-4.5) × 0.8-1 mm. 2n = 14, 28.
Flowering Apr-Jun. Roadsides, fields, pastures, sagebrush hillsides, prairies, railroad embankments, waste places; 300-2200 m; introduced; B.C., Nfld. and Labr. (Nfld.), Ont., Que.; Calif., Idaho, Ill., Mo., Mont., Nev., N.Mex., N.Y., Oreg., Utah, Va., Wash., W.Va., Wyo.; Europe; c, sw Asia; n Africa; introduced also in South America (Chile, Peru).
Isatis tinctoria has been cultivated since ancient times as a source of a blue dye (woad) obtained by fermenting the ground leaves and proximal portions of the plant.