The linear leaves of Athanasia filiformis are scattered up the woody stems. Ascending more on upper stem parts, they may also curve in, their tips pointed. The narrow leaves may be covered in dust-like or mealie grey hairs. Leaf dimensions are 1 cm to 3 cm long by 1 mm to 2 mm wide.

The flowerheads cohere in nearly flat-topped clusters at stem-tips. Each yellow flowerhead comprises many tiny, five-lobed disc florets and, being Athanasia, no rays. A few rows of chaffy bracts form the involucre that holds the florets of each head tightly together. A flowerhead is about 5 mm in diameter.

Flowering happens in spring and summer (Vlok and Schutte-Vlok, 2010; Bond and Goldblatt, 1984; iSpot).