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asp-of-Jerusalem, dyer's woad, woad

Habit 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.

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.

Fruiting pedicels

5–10 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.

Isatis tinctoria

Phenology Flowering Apr–Jun.
Habitat Roadsides, fields, pastures, sagebrush hillsides, prairies, railroad embankments, waste places
Elevation 300-2200 m (1000-7200 ft)
Distribution
from FNA
CA; ID; IL; MO; MT; NM; NV; NY; OR; UT; VA; WA; WV; WY; BC; NF; ON; QC; Europe; c Asia; sw Asia; n Africa [Introduced in North America; introduced also in South America (Chile, Peru)]
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Discussion

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.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Source FNA vol. 7, p. 568.
Parent taxa Brassicaceae > tribe Isatideae > Isatis
Name authority Linnaeus: Sp. Pl. 2: 670. (1753)
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