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.