Dyer's Woad bright yellow,4-petal, flowers in a branched group that is flat/umbrella-shaped.Dyers woad is member of the Mustard family. It is a non-native winter annual, biennial or short-lived perennial, 1 to 4 feet tall. The leaves are alternate, simple, petiolate, bluish-green with a whitish vein on the upper surface of the blade. 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.
Currently not widespread in Colorado, Dyers woad is a serious problem in Utah.
Large, tall bunch of Dyer's Woad Flowers on a wild hillside

Dyer's woad flowers, green seed pods and dried brown seed pods hanging in a bunch along a stem.

Hillside covered in invasive yellow Dyer's woad flowers after a wildfire.