Helianthemum apenninum flowers from March to July, and may grow up to 50 cm tall. The flowers are pentamerous, up to 30 mm across, and are white with yellow centres and yellow stamens. The three outer sepals are hairy and striped; the 2 inner sepals are very small. The flowers grow in clusters of 3 to 10 on a stem.
The leaves are linear to lance-shaped, 30 mm long, in opposite pairs. They are covered with greyish or whitish hairs, especially on the underside, and the edges are rolled under.