Leaves of isocoma rusbyi
are narrow, generally widest in the middle or slightly above. Edges are not toothed but may be somewhat wavy. Leaves have a light-colored midvein and a pair of parallel side veins. Leaves and stems are hairless. Plants often form thick clumps, with dozens of stems growing close together. Stems are reddish brown towards the base.
Flowerheads are produced in small, compact clusters at the top of the stem. The involucre is ringed by between 15 and 25 differently-sized phyllaries, in several rows. Phyllaries have a faint midvein, are sometimes glandular (as are the leaves), and may be either glabrous or lightly hairy. The yellow disc florets number between 19 and 25, and their corollas are about a quarter of an inch long at maturity.