The leaves of Triumfetta sonderi are simple and alternate, growing on short petioles. Small stipules are present on the stems next to the petiole bases.
The leaf-shape is narrowly ovate, tapering to a slightly rounded tip and broadly tapering at the base. Both leaf surfaces are covered in rough hairs with tips split into star-shapes. The leaf margins are finely and irregularly toothed; the serrations tend to disappear near the leaf base. The leaves curve up slightly along their margins, rather than folding along the whitish midribs. A few lateral veins from the midribs are spaced, curving in, becoming less visible near the margins.
The creamy yellow or reddish stems are also covered in dense hairs (Van Wyk and Malan, 1997; Germishuizen and Fabian, 1982).