The inflorescence of senecio rapifolius
is a branched, somewhat elongated cluster containing between 20 and 60 or more heads. Individual flowers are small, about a quarter on an inch across, and easily distinguished from many similar species because they have disc florets only, typically around a dozen, surrounded by 8 phyllaries which are linear, colored light green, sometimes with brownish tips.
Leaves grow mainly around the base; they are long -stalked, have a prominent center vein that may be purplish in color, and are lined by large, ragged teeth. Stems also usually have a purple tint. This species inhabits rocky, partly wooded locations at moderate elevations in mountainous areas.