Name and species circumscription
Austrocactus pauxillus is the name accepted in Plants of the World Online, checked on 10 October 2026. [2-WWW]
The underground part and small above-ground stem
The plant forms a clump of upright stems. Underground sections are almost cylindrical, while above-ground parts are almost spherical, up to 3 cm high and 1.5–3 cm in diameter. The epidermis is dark green, becoming brownish green in sunlight. Seven or eight ribs divide completely into rounded tubercles. [Böhnert et al. 2025, p. 407]
Small oval areoles are slightly sunken. They initially have a small amount of cream-coloured felt and later become bare. Three central spines project from young areoles and lie against the stem on older ones. They may be curved or hooked. Eight to ten radial spines form a comb-like arrangement. They are translucent and needle-like. [Böhnert et al. 2025, p. 407]
A flower larger than the small stem
The funnel-shaped flower measures around 4 cm long and similar in diameter. The lanceolate tepals are pointed, pastel yellow and often faintly reddish in their upper part. The style is yellowish, and the eight stigma lobes are cream-coloured to pale yellow. The dark green pericarpel has few scales and fine white hairs. [Böhnert et al. 2025, p. 407]
The spherical fruit reaches 10–12 mm in diameter. It is dark green and thin-walled, with scales and soft yellowish to white wool. It opens irregularly after drying. Seeds are more round-oval than distinctly comma-shaped, black to brownish black, around 2 × 2.5 mm. [Böhnert et al. 2025, p. 407]
Volcanic fissures and size in cultivation
The revision describes sites on the Mendoza–Neuquén border, east of Domuyo volcano, at elevations of 2350–2500 m. The plant occupies fissures in volcanic rocks and gravel beds, often near a small species of Ephedra. [Böhnert et al. 2025, p. 407]
The authors consider A. pauxillus probably the smallest species in the genus in the wild. In collections, however, plants can grow considerably larger. Stem size alone in a cultivated specimen is therefore insufficient for identification. In tree analyses, the species occupied the earliest-diverging position in section Hiberni, while principal component analysis gave an ambiguous picture of similarity. [Böhnert et al. 2025, p. 390–391, 401, 407]