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Published In: Species Plantarum 2: 670. 1753. (1 May 1753) (Sp. Pl.) Name publication detailView in BotanicusView in Biodiversity Heritage Library

Project Name Data (Last Modified On 8/11/2017)
Acceptance : Accepted
Project Data     (Last Modified On 7/9/2009)
Status: Introduced


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1. Isatis tinctoria L. (woad)

Map 1357

Plants perennial herbs, terrestrial. Stems (30–)40–100(–150) cm long, erect, usually unbranched at the base, many-branched above, glabrous and often glaucous, sometimes sparsely pubescent with unbranched hairs toward the stem base. Leaves mostly 2–15 cm long, the basal and lower stem leaves short-petiolate, the median and upper leaves sessile, clasping the stems, with rounded or acute auricles. Leaf blades oblong or oblanceolate, unlobed, the margin entire or toothed. Inflorescences often several-branched panicles, the lower branches subtended by reduced leaves. Sepals 1.5–2.8 mm long, oblong. Petals 2.5–4.0 mm long, not lobed, yellow. Styles absent. Fruits oblong to oblanceolate or sometimes elliptic-obovate, indehiscent, winged all around, (9–)11–20(–27) mm long, about 3 times as long as wide or less, the seed-bearing portion thickened but somewhat flattened, with a distinct midnerve, the replum absent at maturity, the stalks slender, reflexed, thickened and club-shaped at the tip. Seed 1 per fruit, 2.3–3.5(–4.5) mm long, oblong, light brown. 2n=28. April–June.

Introduced, known thus far only from Jackson County (native of Europe, introduced widely in North America, most abundantly in the western U.S.). Gardens.

This species was used traditionally as the source of woad, a blue dye extracted from the fermented plants. It can become a persistent weed in gardens.



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