Name and species circumscription
Austrocactus decorus is the name accepted in Plants of the World Online, checked on 10 October 2026. [2-WWW]
Stems and strong spines
The plant branches and forms a clump with age. Stems are upright or spreading, shortly cylindrical to columnar, usually up to 20 cm and sometimes 40 cm long, and up to 8 cm in diameter. Around ten ribs divide into prominent, almost round tubercles. Oval areoles are covered with felt. [Böhnert et al. 2025, p. 401]
Seven central spines are very strong and awl-shaped, with a thickened base and fine hairs. Three point outwards and four spread sideways. Around ten radial spines also have a strong, awl-shaped structure and lie in pairs on either side of the areole. They are slightly curved. These features distinguish the plant from A. subandinus, in which some radial spines are much thinner and translucent. [Böhnert et al. 2025, p. 394, 401, 403, 407]
Flowers, fruits and seeds
The funnel-shaped flower is around 6 cm long and similar in diameter. The broadly spatulate tepals are yellow at the base, and beige, lemon-yellow, golden or orange above. The style is whitish to pale pink, and the 9–11 stigma lobes pale yellow to flesh-coloured. The pericarpel bears little white wool and long white bristles. [Böhnert et al. 2025, p. 403]
The shortly oval fruit, around 16 × 18 mm, is green and finely grooved in its upper part. On ripening, it dries and then opens irregularly from the base. The seeds resemble a comma, are dark brown to black and measure around 3 × 2 × 1 mm. [Böhnert et al. 2025, p. 403]
Sites and two growth forms
The revision describes the species in the Chos Malal, Ñorquin and Pehuenches departments of Neuquén Province. It occupies rocky slopes and ridges in open, low shrubby vegetation. Near Chos Malal, plants have stronger, vertically growing stems. In southern Ñorquin, they are smaller and more spreading. [Böhnert et al. 2025, p. 403]
Both forms were included in the genomic-marker analysis. They were associated with A. hibernus, forming a separate lineage also recognisable morphologically. Observations of potential hybrids with A. elegans in the southern part of the Tromen reserve remain a hypothesis requiring further study. [Böhnert et al. 2025, p. 403]