The leaves of common groundsel are alternately arranged and feature deeply lobed margins with irregular teeth. They vary from being sparsely hairy to hairless, and the upper leaves attach directly to the stem while the lower leaves possess short petioles. Leaf undersides, particularly the basal leaves, are often purplish. Seedlings exhibit long, narrow cotyledons with smooth edges. Leaf size typically ranges up to 4 inches (10 cm) long.

The flowers of common groundsel are small and disk-shaped, resembling dandelions. They form in numerous terminal clusters at the tips of branching stems and upper leaf axils. The flower heads, which lack petals, can have a drooping appearance while developing and measure approximately 0.3 inches (8 mm) in diameter. These blooms are yellow and emit a mild, unremarkable scent. The blooming period typically spans late winter to early spring.

The stem of common groundsel is typically single or branched, with a hollow and fleshy structure. It boasts a distinctive purple coloration, which can aid in identification. The stem is relatively thick and robust, providing support for the plant. This characteristic hue and texture make the stem easily recognizable, especially during the plant's active growth period. Branching patterns can vary, with some plants featuring multiple offshoots from the main stem, enhancing its overall structural complexity.

The fruit of common groundsel is an achene, a small, dry, one-seeded fruit that does not open to release the seed. Typically they measure just a few millimeters in length, with a narrow and elongated shape that tapers to a point. Upon maturity, each achene is adorned with a pappus—a tuft of silky white hairs—which aids in wind dispersal. These hairs can be up to 1 inch (2.54 cm) long, providing the fruit with a distinctive appearance resembling a miniature parachute. The color of the achene itself is usually a shade of light brown, and the surface is finely ridged, adding to the fruit's characteristic textured feel.