Isatis tinctoria

Keys to Identification

• Dyers woad is a member of the mustard family. It is a winter annual, biennial or short-lived perennial, 1 to 4 feet tall. The leaves are bluish-green with a whitish vein on the upper surface. The flower has a flat top with yellow petals. The fruit is a purplish-brown pod containing one seed.
• Dyers woad has a thick tap root that can exceed 5 feet in depth. It is found in disturbed sites and spreads to range and croplands by seed from late spring to mid-summer.

This information courtesy of the Colorado Natural Areas Program

Family

Mustard (Brassicaceae)

Other Names

Woad

USDA Code

ISTI

Legal Status

Colorado Noxious Weed List A

Not common in Colorado – Notify your county weed supervisor if you discover this plant

Identification

Lifecycle

Winter annual, biennial, or short-lived perennial

Growth form

Forb

Flower

Flowers are bright yellow and clustered. Late spring.

Seeds/Fruit

Seedpods are black or purplish-brown, one-celled, with a single seed.

Leaves

There are two types of leaves, basal and stem. The basal rosette leaves are 3-4 in, oblong, lance-shaped, and connected to the stem by a petiole. The upper stem leaves are simple, alternate, bluish-green, with a whitish nerve on the upper surface of the blade. These leaves clasp the stem with ear-like projections, and decrease in size toward the top of the stem. All leaves have a slight pubescence and are nearly entire, but occasionally toothed.

Stems

Mature plants are 12-48 in tall.

Roots

It has a thick taproot that may grow 5 ft long.

Seedling

No information available.

Similar Species

Exotics

None known.

Natives

None known.

Impacts

Agricultural

Dyer’s woad reduces forage production in crop and rangelands.

Ecological

Dyer’s woad is an aggressive weed that infests disturbed and undisturbed sites and then spreads outward into crops and rangeland. The BLM projects that infestations of dyer’s woad increase 14% annually, and the Forest Service believes that it has increased several fold on Intermountain forests during the past three decades. There is some evidence that dyer’s woad produces allelopathic chemicals.

Habitat and Distribution

General requirements

Dyer’s woad appears to be well adapted to the physical and environmental conditions of the Intermountain states. It is especially well suited to dry, rocky, soils common to many steep hillsides throughout the western United States. Infestations are frequently observed in rugged inaccessible mountain terrain. Dyer’s woad is also commonly found on disturbed sites, along roadsides, waste areas and rights-of-way.

Distribution

Not yet widespread in Colorado however small populations have been sighted.

Historical

In Europe, dyer’s woad has been cultivated as a source for blue dye and for medicinal properties since the 13th century.

Biology/Ecology

Life cycle

Established dyer’s woad plants begin growth early in the year. The plant has a deep tap root as well as roots near the soil surface. Early growth plus the two-tiered root system probably account for its competitive ability. Undisturbed dyer’s woad plants behave as biennials or winter annuals and typically require portions of two growing seasons to produce seed. Dyer’s woad germinates in the fall or early spring. The seedlings develop rosettes that produce large taproots during the first year. During the winter the plants undergo vernalization. The following spring, new leaves grow from the crown bud in the rosette, and bolting begins. Flowering occurs in late spring, with the exact timing dependent upon elevation.

Mode of reproduction

Reproduces by seed.

Seed production

Hundreds of seedpods, each containing one seed, are produced anywhere from 4-6 weeks after flowering begins.

Seed bank

Seeds do not remain viable in the soil for long periods of time.

Dispersal

No information available.

References

Evans, J.O. 1991. The importance, distribution, and control of Dyer’s woad (Isatis tinctoria). Noxious Range Weeds. Edited by L.F. James, J.O. Evans, M.H. Ralphs, and R.D. Child. Westview Press, Boulder.

McConnell, E.C., J.O. Evans and S.A. Dewey. 1999. Dyer’s woad. In: R.L. Sheley and J.K. Petroff (eds.) Biology and management of noxious rangeland weeds. Oregon State University Press, Corvallis. pg. 231-237.

Whitson, T.D.(ed.), L.C. Burrill, S.A. Dewey, D.W. Cudney, B.E. Nelson, R.D. Lee, R. Parker. 1996. Dyer’s woad. Weeds of the West. Western Society of Weed Science, in cooperation with the Western United States Land Grant Universities Cooperative Extension Services, Newark CA. pg. 228.