Stems of lenecio lemmonii
are purplish near the ground, green higher up, and bear closely-spaced leaves at alternate intervals, clasping or heart-shaped at the base. Leaves have a pronounced midvein and fainter side veins, and are lined with sharp, irregular teeth. Plants are generally hairless, apart from little tufts of white hairs on the upper side of the leaf axils.
The inflorescence is an open, flat-topped cluster of 4 to 12 flowerheads, which have about 8 or 13 yellow ray florets (occasionally zero), and several dozen ray florets. The involucre is surrounded by 21 equal-length phyllaries, all green except for the very tips which are black. Below these are 3 to 5 (or more) thin, much shorter bractlets, generally not spreading. Flowerheads are about one inch in diameter, and the rays are relatively broad, and indented at the tip.