Description from Flora of China
Isatis indigotica Fortune; I. oblongata de Candolle var. yezoensis (Ohwi) Y. L. Chang; I. tinctoria var. indigotica (Fortune) T. Y. Cheo & K. C. Kuan; I. tinctoria var. yezoensis (Ohwi) Ohwi; I. yezoensis Ohwi.
Herbs biennial, (30-)40-100(-150) cm tall. Stems branched above, glabrous and somewhat glaucous, or hirsute, often paniculately branched. Basal leaves rosulate; petiole 0.5-5.5 cm; leaf blade oblong or oblanceolate, (2.5-)5-15(-20) × (0.5-)1.5-3.5(-5) cm, base attenuate, margin entire, repand, or dentate, apex obtuse. Middle cauline leaves sessile; leaf blade oblong or lanceolate, rarely linear-oblong, (1.5-)3-7(-12) × (0.2-)0.8-2.5(-3.5) cm, base sagittate or auriculate and with acute or obtuse auricles, margin entire, apex acute. Fruiting pedicels slender, considerably thickened and subclavate at apex, 5-10 mm. Sepals oblong, 1.5-2.8 × 1-1.5 mm, glabrous. Petals yellow, oblanceolate, 2.5-4 × 0.9-1.5 mm, base attenuate, apex obtuse. Filaments 1-2.5 mm; anthers oblong, 0.5-0.7 mm. Fruit black or dark brown when mature, oblong-oblanceolate, elliptic-obovate, or rarely oblong, (0.9-)1.1-2(-2.7) cm × 3-6(-10) mm, often broader above middle, glabrous or pubescent, winged all around, base cuneate, margin sometimes slightly constricted, apex subacute, rounded, or rarely subemarginate; locule 3-6(-10) mm, with a distinct midvein and inconspicuous lateral veins; apical wing 3.5-5(-7) mm wide. Seeds light brown, narrowly oblong, 2.3-3.5(-4.5) × 0.8-1 mm. Fl. Apr-Jun, fr. May-Jul. 2n = 14, 28*.
The above first record of Isatis tinctoria from Xizang is based on Falconer s.n. (K). Isatis tinctoria is a European and probably Asian species very polymorphic in fruit shape, shape and size of auricles of cauline leaves, and the amount of indumentum. It has been cultivated since ancient times as a source of a dark blue dye (woad) obtained by fermenting the leaves and lower portions of the plant. Glabrous forms with oblong fruit and poorly developed or obtuse leaf auricles have been recognized as I. indigotica. By contrast, glabrous or hairy forms with cuneiform or oblong-triangular fruit and well-developed, often acute leaf auricles are called I. tinctoria. However, every conceivable morphological intermediate between the two forms occurs in China, as well as elsewhere in Asia, Europe, and North America, where they are introduced and naturalized.
The roots and leaves are used for medicinal purposes and a source of dye, and the seed oil is used in industry.
Fields, pastures, roadsides, waste places; 600-2800 m. Fujian, Gansu, Guizhou, Hebei, Henan, Hubei, Jiangxi, Liaoning, Nei Mongol, Shaanxi, Shandong, Shanxi, Sichuan, Xinjiang, Xizang, Yunnan, Zhejiang [Japan, Kazakhstan, Korea, Mongolia, Pakistan, Russia, Tajikistan, Uzbekistan; SW Asia, Europe; naturalized elsewhere].