Submodule 5: Most Common Western Rangelands Weeds

Yellow Starthistle

Yellow starthistle (Centaurea solstitialis) develops into a gray-green to blue-green herbaceous plant that grows from 6 in to 5 ft (15 cm to 1.5 m) tall, and has deep taproots. It is a winter annual (or at times a biennial or short-lived perennial) that germinates in late fall or early spring. After germination, it first forms a rosette with deeply lobed leaves that are close to the ground. These leaves are generally less than 2 inches wide but can be up to 8 inches long. In late May or early June, it bolts, producing stems that are winged, erect, and branching. Each ends with a composite inflorescence containing bright yellow florets. Sharp, tan-colored, star-shaped spines surround each flower base can be up to 2 in (5 cm) long and can be very painful if touched. The stems and leaves are covered with cottony wool. Lower leaves are 2 to 3 inches (6 – 7 cm.) long and deeply lobed. Upper leaves are shorter (0.5 to 1.0 in; 1 to 2.5 cm) and narrower, with few lobes.

(photo courtesy Larry Howery)