The genus in two taxonomic treatments
Plants of the World Online accepts 16 species of Austrocactus. Böhnert and colleagues' 2025 revision recognises 17. The difference concerns the rank of one plant. Austrocactus coxii subsp. longicarpus is a subspecies in POWO, while the revision's authors recognise the separate species A. longicarpus. They support its distinctness with morphology and its position on the phylogenetic tree. Atlas descriptions retain the POWO name and assign the revision's results precisely to the subspecies studied. [Böhnert et al. 2025, p. 393, 401, 406–407] [2-WWW] [2-WWW]
The former Austrocactus patagonicus and A. dusenii fall within A. bertinii. The name A. gracilis refers to the nominate subspecies of A. coxii. In collections, it was also sometimes misapplied to plants from near Zapala, later described as A. longicarpus. Identifying such a specimen requires linking its name to its origin, flower structure and the way its fruit opens. [Böhnert et al. 2025, p. 396–397, 406–409] [2-WWW] [2-WWW]
Stems, areoles and underground parts
Stems may grow upright, spread over the ground or form compact clumps. In most species, the ribs are divided into tubercles, with round or oval areoles on their tips or in depressions. These are short shoots producing spines and flowers. Young areoles have felt or wool, whose amount changes with age. Central spines differ from radial ones in strength, orientation and sometimes hooked tips. In some species, the distinction between these two groups remains unclear. [Böhnert et al. 2025, p. 393–394, 403, 407]
Root system structure varies. The revision describes fibrous and fleshy roots, less often a distinct taproot. The creeping stems of A. coxii subsp. coxii and A. hibernus subsp. hibernus produce adventitious roots. A. spiniflorus is particularly different. It has a strong tuberous root, rhizomes and underground stem sections, while the ribs of its above-ground stems remain smooth, without division into tubercles. [Böhnert et al. 2025, p. 391, 403, 409, 413–414]
Flowers and fruits as identification features
Flowers are funnel-shaped, bell-shaped or broadly bowl-shaped. The exterior of the floral tube and the lower covering around the ovary, called the pericarpel, bear scales, wool, hairs, bristles or thin spines. Stamens are arranged in two series. The style projects above them and ends in a stigma divided into lobes. Its colour, from pale yellow to deep violet, is an important feature in the identification key. The revision does not establish the role of these colours in pollinator choice. [Böhnert et al. 2025, p. 393–394]
The fruit may be spherical, barrel-shaped, elongated or club-shaped. Species differ in the amount of wool and bristles and in fruit consistency after ripening. In many, the fruit dries and opens from the base. In A. coxii subsp. longicarpus, it splits lengthwise. Fruits of both A. hibernus subspecies are succulent, and the mature fruit of A. spiniflorus is yellow and highly mucilaginous. The mostly flattened seeds resemble a comma and have a sculptured seed coat. [Böhnert et al. 2025, p. 393, 403, 406, 409, 413–414]
Patagonia and the Andes
The genus occurs in Argentina and Chile. The revision presents both widely distributed plants of the Patagonian steppes and local mountain endemics. A. aonikenkensis occupies sandy and gravelly plains from the coast to the Andean foothills. A. ferrarii grows in gravel beds and rock fissures in the Sierra del Tontal. A. praecox, A. elegans and A. pauxillus are associated with volcanic substrates, while A. subandinus was also found on limestone rocks. Differences between these sites form part of each species' biology. [Böhnert et al. 2025, p. 396, 399, 401, 403, 407]
The distribution compilation used 764 field observations assigned to taxa following the revision. Most observations came from Elisabeth and Norbert Sarnes, and many lacked a separate herbarium specimen. Herbarium data supplemented this material. The map therefore represents extensive fieldwork, with uneven documentation of sites. Each species' detailed description follows the range established in the revision, and its name status follows current POWO. [Böhnert et al. 2025, p. 387–388, 391]
Relationships established from genomic markers
The study included 44 Austrocactus samples representing recognised species and morphological forms. DNA mostly came from first-generation plants raised from wild-collected seeds. The ddRADseq analysis compared DNA fragments scattered across the genome. Trees were calculated by maximum likelihood and by a quartet method under a coalescent model, which considers the history of separation of gene copies. Both approaches confirmed the common ancestry of the genus and its sister relationship to Eulychnia. [Böhnert et al. 2025, p. 387–390]
In the authors' classification, A. spiniflorus forms the separate subgenus Spiniflori. The remaining species belong to subgenus Austrocactus and three sections. Coxiani groups plants with strongly woolly fruits, Hiberni groups species with mostly pale stigmas, and section Austrocactus groups species with purple stigmas and less woolly fruits. This is the 2025 revision's arrangement, in which A. longicarpus belongs to Hiberni. POWO's retention of this taxon in A. coxii shows that the current database circumscription and proposed phylogenetic classification still differ partly. [Böhnert et al. 2025, p. 393–394, 401, 407, 411–413] [2-WWW]