This is an annual weed, reproducing by seeds. The stems are erect, 1-4 ft. high, hollow, and glabrous. The leaves are alternate with spiny and deeply lobed margins. Lower leaves are petiolate while the upper leaves are sessile. Leaf veins may be purple.
Flower heads are numerous, yellow, and appear in corymbs.
The seeds are flat achenes, approximately 3 mm long, ribbed lengthwise, brown, with a pappus of white hair at one end. This weed germinates anytime between spring and fall when conditions are suitable. Annual sow-thistle thrives where moisture is available, especially disturbed areas resulting from overgrazing, natural processes or cultivation. This weed may compete with other desirable plant species. The seeds are easily disseminated by the wind due to the pappus of white hair at one end.