Pterocactus australis

Segments and spines

Segments are globose or obovoid, with a broader tip, and have a brown-purple surface divided into tubercles. In the 2021 comparison, areoles lack conspicuous wool. The central spine is flat and may reach about 20 mm. The flower forms at the segment apex. [Las Peñas and Bernardello 2021, Table 2]

Historical and field material showed substantial spine variation. Some specimens have strong, spreading spines, while others have flat, papery ones. This variation occurs alongside a low habit in which segments may be sheltered by neighbouring vegetation. [Kiesling et al. 2021]

Patagonia and name history

The species occurs in Argentina and Chile. The typification account describes sites from the Río Negro coast to Santa Cruz, across the Patagonian plateau, and in Chile's Aysén region. Plants were also found near water and in places somewhat moister than the surrounding terrain. [Kiesling et al. 2021]

The historical material came from the expedition of the ship Le Volage, sent to Patagonia to observe the 1882 transit of Venus. Couteaud collected the plant, and J. F. Heimsch made the drawing. Weber described the species in 1898. In the 2021 paper, the illustration was designated as a neotype, with an additional epitype specimen helping interpret the name. [Kiesling et al. 2021]

Microscopic surface and pollen

Epidermal cells may form straight papillae with a striated base and smooth tip. The cuticle between them is relatively smooth. In the anther study, mature pollen was bicellular, with pores across its surface. Among the four species compared, P. australis had the fewest pores. [Faigón et al. 2011] [Gotelli et al. 2009]

Genetic diversity

The material studied had a count of 2n = 44. Two specimens used in the chloroplast analysis did not form a shared exclusive group but fell into the genus's two main lineages. The authors considered historical gene flow and the need to analyse nuclear markers. The chloroplast result leaves the origin of this difference open to explanation. [Las Peñas and Bernardello 2021]