Click on image to enlarge. Yellow starthistle is a warm season annual weed. Seedlings are dull green.
Seed leaves are oblong, round at the tip, with smooth edges.
The first true leaves are longer and narrower with short, white hairs on the upper surface. Mature plants are 1 to 3 feet tall. The bases of the grayish leaves extend down the stem. The bright yellow flowers have long stiff spines at their base. There is a parachute seed structure that is carried by the wind.