Seriphium plumosum has tiny leaves tufted up its erect, branching stems. The leaves are grey, granular and hairy. The plant is from 30 cm to 1,2 m tall.
The flowerheads grow in dense clusters at stem-tips. Each purple to brown flowerhead is one-flowered, the bisexual flower of the discoid type, i.e. no ray florets. The involucre comprises several rows of tiny bracts.
Flowering occurs mainly from mid-autumn to early winter (Leistner, (Ed.), 2000; Bond and Goldblatt, 1984; iNaturalist).