Acaena exigua is a small perennial rosette herb in the rose family (Rosaceae) with narrow, fern-like, divided leaves and slender flowering stalks 5 to 15 cm (2 to 5.9 in) long. The narrow, oblong leaves are usually 10 to 25 mm (0.4 to 1.0 in) long with 6 to 17 leaflets 1 to 4 mm (0.04 to 0.16 in) long and 1 to 2 mm (0.04 to 0.08 in) wide. The leaflet on the end is wider (to 3 mm (0.12 in). The upper surface of the leaves is glossy with conspicuous veins; the lower surface is whitish. The flowers lack petals and are arranged in short, dense spikes 5 to 10 mm (0.2 to 0.4 in) long held on slender, sparsely leafy stalks 5 to 15 cm (2 to 6 in) tall. The base of the flower is urn-shaped, sometimes with very short spines or bristles, and encloses a single cone-shaped dry fruit (achene) 1 mm (0.04 in) long.