Argentina. Jujuy: Sierra Santa Barbara, 2500 m, 11 Ju1 1901, Fries 264 (lectotype designated by Simpson 1979, pg. 56: S!; isolectotype: US!).

Trees 3–8 m tall. Leaves slightly congested at the branch tips, imparipinnate with 2–3 pairs of leaflets, obtrullate in outline, (2.0–)3.7–6.1(–7.2) × (1.8–)2.9–4.1(–5.3) cm; rachises sparsely hispid, points of leaflet attachment with a tuft of long white hairs; stipular sheaths glabrescent or sparsely to densely villous with long hairs; leaflets elliptic in outline, second pair from the terminal leaflet the largest, one of this pair (1.0–)1.6–2.9(–4.0) × 0.6–1.5 cm; margin serrate with 9–13 teeth, apically emarginate, basally unequally cordate; upper leaflet surfaces glabrous; lower leaflet surfaces glabrous or sparsely hispid. Inflorescences pendant, (1.8–)4.2–5.0(–7.3) cm long, bearing 5–12 flowers; floral bracts 2.1–3.1 mm long, narrowly triangular; rachises villous. Flowers 4.4–8.5 mm diam.; sepals 4, ovate, green, densely villous outside; stamens 10–22, anthers orbicular, with a dense tuft of straight white hairs on the upper half; styles fimbriate, 0.9–2.0 mm long. Fruits turbinate, with 2–3 irregular and pronounced thin wings, glabrous; 4.4–7.9 × 5.0–6.8 mm including wings. Diploid, triploid, tetraploid and hexaploid.

Polylepisaustralis is endemic to Argentina, where it is distributed from the northern Andes (Jujuy Province) to the central Sierra de Córdoba (Córdoba Province) Argentina (Fig. 73). It occurs in humid subtropical mountains, as well as in dry forest at 1230–3800 m elevation. The northernmost populations of P.australis have higher genetic differentiation and lower genetic population diversity than southern and central populations (Hensen et al. 2011). Possibly, gene flow in the northern stands is restricted by geographic isolation, whereas the southern and central populations may be connected by effective long-distance pollination (Hensen et al. 2011). Dendroclimatic analyses from central Argentina show that growth of P.australis at intermediate and high elevations growth is more strongly related to temperature than to rainfall (Lanza et al. 2018). Populations at the upper and lower elevational limits of the species are adapted to the respective climatic conditions, which should be considered in conservation action (Marcora et al. 2021). In many regions, P.australis is confined to areas with high rock proportion, to where they have been restricted due to fires and long-term grazing pressure (Suarez et al. 2008). Polylepisaustralis forms shrublands on ridges with poor, leached soils exposed to wind and frost and woodlands in sheltered ravines. The most critical stage of the species regeneration cycle in the shrublands is the transition from seedling to saplings, whereas in the woodlands, it is seed germination (Enrico et al. 2004). Overall, seed germination rates in P.australis are low at 0% to 14% (Enrico et al. 2004; Renison et al. 2004; Menoyo et al. 2009; Pollice et al. 2013). Germination rates are higher in areas with reduced livestock density which have lower insect predation and fungal fructifications (Menoyo et al. 2009). Seed production increases with tree height, with highest seed production in areas without livestock. Seed mass also increases with tree height, but there is no livestock effect (Pollice et al. 2013). Seed viability is associated with relatively undisturbed soils with no erosion, suggesting a connection to nutrients and/or water stress (Renison et al. 2004). Maximum seed dispersal distance in P.australis is 6 m and seedlings are found no more than 10 m from seed trees (Torres et al. 2008). However, extensive pollen flow between isolated fragments reduces the negative effects of seed quality resulting from reproductive isolation and inbreeding (Seltmann et al. 2009b). Seedling establishment is severely affected by livestock, so that there are more seedlings and seed trees in areas with less livestock than in degraded regions with historic and current grazing impact (Renison et al. 2006; Torres et al. 2008; Menoyo et al. 2009; Marcora et al. 2013). Livestock has considerable impact on soil degradation in the mountains of central Argentina (Renison et al. 2010), and these vegetation-soil alterations reduce the soil water storage capacity of P.australis woodlands (Poca et al. 2018). Polylepis forest in central Argentina have high polypore (wood-decay fungi) species richness in mature forest, with numerous threatened and rare species (Postiacaesia, Fuscoporiagilva, Polyporusarcularius and Ceriporiaspissa) found in the presence of large logs (Robledo and Renison 2010). Similarly, there is a high diversity of lichens (Rodriguez et al. 2020). In the southern Yungas (Jujuy Province), the P.australis forests have high bird diversity, but Polylepis specialist bird species are absent, possibly because these are small patches (Bellis et al. 2014). However, active forest restoration measures have locally increased bird diversity and abundance over 20 years (Barri et al. 2021).

The EOO for Polylepisaustralis is estimated as 151,750 km², the AOO is assessed at 604 km² and it is known from 73 locations. Polylepisaustralis has the most extensive forest in the southern sector of the Quebrada del Condorito National Park and surrounding private fields in Córdoba Province. The best-preserved stands are located near the town of Los Molles at 1500–2650 m (Renison et al. 2013). In many stands of P.australis, there is evidence of fire that is set to induce grass regrowth as feed for livestock (Renison et al. 2002, 2006, 2013; Argibay and Renison 2018). Fire, logging and browsing affect P.australis forests and a reduction of such disturbances would increase the area covered by these forests and the vitality of the trees (Renison et al. 2011, 2013; Cáceres et al. 2021). However, moderate livestock densities are compatible with forest conservation, if properly managed (Giorgis et al. 2020). Polylepisaustralis is also affected by the invasion of exotic woody species, such as Pinus sp. planted in large areas in Córdoba Province, as well as other species like Cotoneasterfranchetii, Betulapendula, Rosarubiginosa, Rubusulmifolius, Salixviminalis and S.aff.fragilis (Renison et al. 2013). Vegetation cover is very low in P.australis forests, so that it is common to observe bare roots as an evidence of soil erosion (Cingolani et al. 2008; Renison et al. 2010, 2013). Nevertheless, P.australis can regenerate even under such conditions, possibly due to the long history of fire in the region (Cingolani et al. 2014; Torres and Renison 2017). Polylepisaustralis has been subject to reforestation activities in Córdoba since 2002 (Renison et al. 2002; Aráoz and Grau 2010; Renison et al. 2013). Seedling growth is six times slower in sowing experiments than the growth of planted P.australis (Landi and Renison 2010). Thus, planting and not seeding has become the preferred method to re-establish this species. In addition, the construction of terraces with Poastuckertii as a nursery plant has been suggested. Moreover, biparental inbreeding depression is found especially in plants that cross with nearby neighbours (Seltmann et al. 2009a). This is more important to progeny fitness and mortality than to germination. Additionally, crosses between fragments have higher reproductive output than within-fragment crosses. We assess P.australis as Least Concern (B1a+B2a).

Polylepisaustralis is easy to recognize by its glabrous leaflets (sometimes the lower leaflet surface can be sparsely hispid) and by its winged fruits, a character shared only with P.neglecta. Specimens of P.australis can resemble those of P.neglecta in leaflet shape, size and margin, but leaflet apices are emarginate in P.australis and acute in P.neglecta. Further, P.australis differs from P.neglecta by it simple and villous inflorescences with 5–12 flowers, whereas P.neglecta usually has branched and glabrous inflorescences with 14–27 flowers.

Polylepisaustralis is morphologically quite variable, as evidenced by the large number of varieties recognized by Bitter (1911). More recent studies have shown that P.australis also has high variability of ploidy levels (Schmidt-Lebuhn et al. 2010; Kessler et al. 2014). In a study of 361 individuals, Kessler et al. (2014) found that, in the Andean part of the distributional range of the species, most populations are purely diploid (except at the southernmost tip of the Andean range), whereas in the isolated Sierra de Córdoba, tetraploids dominate, but there are also diploid and triploid plants and even a single hexaploid plant was found. This diversity of ploidy levels raises several important questions. First, the degree to which the di- and tetraploids are reproductively isolated and might, therefore, be treated as distinct taxa, is unknown. Soltis et al. (2007) have proposed that populations of a species with different ploidy levels should be treated as distinct species if there is evidence of reproductive isolation or if they are morphologically or ecologically distinct. In the case of P.australis, the different geographical ranges of the two main ploidy levels suggest that they have independent evolutionary trajectories. If this is confirmed, since the type collection of the species comes from the purely diploid part of the range, the unnamed form would be the tetraploid one. Following Soltis et al. (2007), a suitable name would be Polylepistetra-australis. Second, it is unknown whether the triploid individuals are only first-generation hybrids between di- and tetraploids or are also able to reproduce by apomixis, as is common in many Rosaceae. Indeed, the low rate of seed germination of many individuals (Enrico et al. 2004; Renison et al. 2004; Menoyo et al. 2009) may be linked to the triploid ploidy level, but this also remains to be explored.

Argentina. Catamarca: Andalgalá, East slope of Nevados de Aconquija, Estancia “Yunca Suma”, Los Queñoales, 27°22'S, 066°02'W, 2400 m, 20 February 1966, Hawkes 3547 (MO!). Córdoba: Calamuchita, Sierra Grande (Falda E), al pie del Cerro Champaquí, 2200 m, 26 September 1952, Hunziker 9942 (MO!); La Cumbrecita, 31°55'S, 064°15'W, 1450 m, 17 December 1978, Solomon 4200 (MO!). Punilla, Dpto. Punilla, cerca del río Yatain, 18 November 1971, Ancibor 2150 (MO!); Tanti, Ruta n° 20, km 757, 26 April 1963, Ariza 1604b (CORD); Cerro Los gigantes, 50 km west of Córdoba, 2000–2050 m, 27 January 1974, Conrad 2455 (MO!); Barranca de Río Yuspe (Puente), 1780 m, 16 December 1949, Meyer 15627 (GOET!). San Alberto, Pampa de Achala, 2200 m, 13 December 1945, Hunziker 1398 (MO!); Pampa de Achala, ca. 40 km E Mina Clavero on road to Córdoba, 1900 m, 13 November 1991, Kessler 3347 (AAU!, GOET!, MO!); 3348 (GOET!, MO!); 3349; 3350 (AAU!). Jujuy: Capital, Lagunas de Yala, 2100–2300 m, 18 November 1986, Charpin AC 20520 (MO!). Jujuy, Jala-Reyes, 30 October 1982, Zardini 1587 (MO!). Sierra La Barbara, 2500 m, 11 July 2001, Fries 264 (US!). Valle Grande, Camino a Altos de Calilegua, 2400 m, 31 October 1974, Cabrera 25659 (MO!). Salta: Guachipas, Alto del Poronguito, 1900–2000 m, 07 February 1983, Novara 3157 (MO!). Santa Victoria, 15 km. from Santa Victoria towards La Quiaca, 22°15'S, 065°04'W, 3300–3400 m, 05 April 1979, Bothmer 6466 (MO!); Santa Victoria, ruta 5, alturas 10 km al W del pueblo, 2900 m, 14 May 1987, Novara 6695 (GOET!, Z!); Santa Victoria, por el camino 5–10 km al W del pueblo, 2700–3000 m, 10 November 1988, Novara 8210 (Z!); Santa Victoria Oeste, 22°15'00"S, 064°58'00"W, 21 January 1983, Zardini 1676 (MO!); La Huerta, 31 January 1983, Zardini 1903 (MO!); San Luis: Junín, Sierra de Comechingones, al este de Merlo, ruta prov. 5, 1200 m, 16 December 2000, Leuenberger 4764 (GOET!); 5 km al este de Merlo (El Mirador), 26 January 2001, Scarpa 435 (SI). Tucumán: Chicligasta, Saladillo, 1000 m, 18 May 1948, Meyer 14063 (MO!); 1800 m, 10 March 1924, Venturi 3010 (Z!); 2000 m, 13 December 1925, Venturi 3990 (MO!). Tafí, Quebrada de los Alisos Tafi del Valle, 01 January 2012, Castillón 89344 (US!); Tafí del Valle, 2000 m, 24 September 1949, Palacios 19Ar106 (MO!); Tafí del Valle, 26°47'28"S, 065°43'48"W, s.d., Palacios s.n (MO!); Localidad La Cienaga, 2800 m, 29 January 1950, Sleumer 204 (GOET!). Trancas, 01 August 2017, Schreiter 321 (MO!); Tafi del Valle, 19 December 1965, Walter 614 (GOET!).