(Isatis tinctoria)
Description
This distinctive plant belongs to the mustard family and can be a winter annual, a biennial or a short-lived perennial. It can grow up to four feet in height and has bluish-green leaves covered with fine hairs. Leaves are alternate with a prominent cream colored mid-vein, especially noticeable on the rosettes. When this plant bolts, it can produce up to 20 stems, and it grows and sets seed very quickly. Yellow flowers bloom from May to August, depending on climate and they are similar in appearance to common mustard flowers. Flowers are found in clusters at the end of the branch tips. When flowers go to seed, the large blackish- blue seed pods are very distinquishable. This plant spreads primarily by seed and has a taproot that can reach up to five feet in depth.
Key Features
The key identifying characteristic of dyers woad is the dark seed pod at seed set. Areas infested with dyers woad resemble areas affected by wildfire due to these dark pods.
Habitat
Dyer’s woad prefers dry, rocky soils common to many side hills. It can be found in rocky and sandy soils with very little water availability. It is found in dry pastures, uncultivated fields, roadsides, waste areas, rights-of-ways, forest, and rangeland.
Currently found in the following counties:
Beaverhead,Carbon, Flathead, Gallatin, Missoula, Park, Silver Bow
IWM
Interesting Facts
The use of dyer’s woad dates from ancient times when Romans stained their body with the plant. Dyer’s woad was introduced into North America during the colonial period and was used before indigo dye became available. It apparently then spread, through contaminated alfalfa seed shipments, to the West, where it has become a nuisance in range, cropland, and forest.
Commonly Confused Plants
- Common mustard
Photo Credits: Steve Dewey, Utah State University, www.bugwood.org; Joseph M. DiTomaso, University of California - Davis, www.bugwood.org; Becky Kington