Peru. Arequipa: Pampa behind train station, Arequipa to Puno line, 3800 m, Weberbauer 4881 (holotype: B destroyed; isotype: WRAT!).

Trees 2–12 m tall. Leaves slightly congested at the branch tips, imparipinnate with pair of leaflets, obtrullate in outline, 2.0–2.8 × 1.6–2.5 cm; rachises densely tomentose, points of leaflet attachment with a tuft of long hairs; stipular sheaths apically truncate, densely tomentose on the outer surfaces; leaflets broadly obovate in outline, second pair from the terminal leaflet the largest, one of this pair 1.2–1.6 × 0.6–0.9 cm; margin crenate with 5–8 teeth, apically obtuse or emarginate, basally unequally attenuate; upper leaflet surfaces strongly rugose, glabrous; lower leaflet surfaces densely tomentose with whitish hairs 0.8–1.0 mm long, mixed with a dense layer of very short, white pannose hairs. Inflorescences pendant, 4.2–7.8 cm long, bearing 4–5 flowers; floral bracts 4.6–4.9 mm long, narrowly triangular, densely tomentose on the outer surface; rachises tomentose. Flowers 6.7–9.9 mm diam.; sepals 4, ovate, green, densely tomentose outside; stamens 11–15, anthers orbicular, with a dense tuft of straight white hairs on the upper half; styles fimbriate, 2. 1–3.5 mm long. Fruits turbinate, with 2–3 irregular flattened ridges with a series of spines, densely villous; 4.5–6.2 × 4.9–7.5 mm including spines. Tetraploid.

Polylepisrugulosa is distributed in Peru from western Arequipa, southern Cusco, Moquegua and western Tacna to northern Chile (Arica and Parinacota) (Fig. 103). It occurs in very dry Andean habitats with rocky soils at 2900–4550 m elevation. In Peru, average tree height of P.rugulosa is 1.0–1.5 m, with diameters typically less than 10 cm and tree density of 583 individuals ha^-1 (Rodríguez 2018). The highest density of adult trees and seedlings was found at 4300 m elevation (38% slope) and the lowest density and coverage at 4180 m elevation (20% slope), suggesting a preference for areas with steeper slopes or higher presence of rocks and shrubs. Seedling density was significantly higher under the crowns of Polylepis trees than under isolated bushes (Rodríguez 2018). Polylepisrugulosa populations in the pre-altiplano zone on the western slopes of the Andean Cordillera of northern Chile have an age structure that suggests highly episodic seedling establishment, due to sequences of wet years (Rundel et al. 2003). The maximum photosynthetic capacity of P.rugulosa in the wet season is 6.4 μmol m^-2s^-1, although it can maintain relatively high rates of photosynthesis throughout the year (Rundel et al. 2003). Furthemore, P.rugulosa responds to elevation by changing in morphology (short trees with small leaves) and ecophysiological responses (decreased transpiration rate, higher nutrient concentration and enrichment in the ¹³C isotope suggesting more water stress) (Macek et al. 2009). In a population at 3700 m elevation, P.rugulosa had 34% higher total chlorophyll content during the morning hours, apparently due to de novo synthesis of both Chla and Chlb (García-Plazaola et al. 2015). In a dendrochronological study in Parinacota (Chile), average radial growth of P.rugulosa was 0.7 mm a^-1 (Silva 2012). Growth of P.rugulosa is determined by precipitation during the wet season of the preceding and growth years (Jomelli et al. 2012). Based on Amplified Fragment Length Polymorphisms (AFLP), extensive gene flow has been found to occur within and between Chilean populations (Schmidt-Lebuhn et al. 2006b). Polylepisrugulosa patches harbour specialized and endangered bird species (Miranda and Cardozo 2008; Samata et al. 2019).

The EOO for Polylepisrugulosa is estimated as 35,293 km², the AOO is assessed at 172 km² and it is known from 24 locations. The extent of P.rugulosa forests in Arequipa (Peru) is estimated at 76,566 ha, where large forests are found around Ampato Volcano (20,114 ha), Pichupichu Volcano (5,395 ha) and at the high Andes of Yura (Esquerra 3,249 ha and Palca 1,071 ha) (Jururo 2018). Only small extents of P.rugulosa forest are currently protected in Chile within Lauca and Volcán Islunga National Parks, Las Vicuñas National Reserve and in Peru in Chili-Quilca (Arequipa) in the buffer zone of Salinas y Aguada Blanca National Reserve. The species was categorized as VU (A1c) in the World List of Threatened Trees (Oldfield et al. 1998). In Peru, it has been categorized as VU (SERFOR 2006) and, in Chile, as VU (Benoit 1989; Miranda and Cardozo 2008). Polylepisrugulosa has been harvested for fuel in the early 20^th century and is severely impacted by the mining activity in Chile (Rundel et al. 2003). We assess P.rugulosa as Vulnerable (B1a+B2a, C1).

Polylepisrugulosa is similar to P.subtusalbida, but has just one lateral leaflet pair and broader leaflets (0.6–0.9 mm wide) with crenate margins, whereas the latter has 1(–2) pairs and narrower leaflets (0.4–0.6 mm wide) with serrate margin. Polylepisrugulosa also has longer inflorescences (4.2–7.8 cm) with 4–5 flowers and 11–15 stamens (P.subtusalbida 1.8–3.7 cm, 3–4 flowers and 19–21 stamens). Mendoza and Cano (2012) considered that both P.rugulosa and P.subtusalbida occur in southernmost Peru, but according to our assessment of these species, only P.rugulosa occurs in this region, whereas P.subtusalbida is endemic to central Bolivia. For additional morphological similarities, see under P.besseri.

Chile. Arica and Parinacota: Putre, 3500 m, 02 May 1987, Fjeldså s.n (AAU!). Tarapacá: Región de Tarapacá, Strasse von Zapahuira zum Portezuelo de Chapiquiña, s.d., Hellwig 513 (G).

Peru. Arequipa: Arequipa, Cerca a Chiguata. SE de Arequipa, 3000–3500 m, 23 September 1966, Arenas 34 (USM!); Dist. Pocsi; Tuctumpaya, 3200 m, 03 April 2003, Cáceres 3212 (USM!); El Cimbral-Chiguata, 3900 m, 09 November 1996, Cáceres 47 (CUZ!); Arequipa/Puno:. Sihuata-La Cumbre, 3800–4000 m, 13 November 1947, Ferreyra 2594 (GOET!, MO!, US!, USM!); Chiguata, arriba de Miraflores, 3800 m, 10 November 2002, Quipuscoa 2810 (F!); Chiguata, 16°23'11"S, 071°20'19"W, 4000–4250 m, 13 February 2003, Quipuscoa 2857 (F!); Simbral, carretera de Chiguata-Juliaca, 3500–4000 m, 30 May 1999, Roque 880 (USM!); road to Chacayani to Chiva, 16 January 1977, Simpson 8570c; 8570d (USM!); Hacia el Cimbral, 3750 m, 11 April 1959, Vargas 12687 (CUZ!); Chiguata-Cimbral, 3700–4000 m, 13 October 1976, Vargas 22849 (CUZ!). Caylloma, Huambo. Dist. de Huambo, 4000 m, 03 October 1990, Rodriguez 2 (USM!); Dist. de Huambo, 4000 m, 01 August 1990, Rodriguez 3 (USM!); Huambo, Dist. Huambo, 3800–4200 m, 01 August 1990, Rodriguez 4 (USM!); 5 (USM!). Cayma, Estancia Cabrarias. Chacani. Norte de Arequipa, 3500–4000 m, 14 January 1966, Arenas 12 (USM!); Nevado Chachani, along dry stream-beds in open rocky valley, 4000–4200 m, 14 April 1925, Pennell 13295 (F!, US!); Volcan Chachani, on the road to the summit. Km 32 on the road from Chachani to Chivay in shallow ravines, 16 January 1977, Simpson 8570 (A!, MO!); 8570b (USM!). Chiguata, 10 km above Chihuata (W slope of Misti), 16°24'S, 071°24'W, 4270 m, 07 April 1987, Boertmann 144; 145; 146; 147 (AAU!). Condesuyos, alturas cordilleranas, 4200–4600 m, 24 April 1967, Vargas 19466 (CUZ!). Cotahuasi, Camino a Cotahuasi, 3735 m, 30 June 2004, Cáceres 3824 (USM!). Huambo, Huambo (Quebrada Sau Sau), 4000 m, 29 August 1987, Espinoza 7 (USM!). La Union, Dist. Cotahuasi; vista del condor, 3200 m, 05 June 2002, Cáceres 5457 (USM!). Orcopampa, Orcopampa-Huancurama, 3875 m, 17 August 1987, Huamani 11 (USM!). Pampacolca, Chuquibamba-Pampacolca, 4000m, 13 August 1987, Huamani 8 (USM!). Yura, Yura-Huanca, 3200 m, 09 June 1999, Roque 1048 (USM!); Quebrada Chontahuayco y Monte Barranco, 4020 m, 01 August 1987, Espinoza 1 (USM!); 4050 m, 11 August 1987, Espinoza 5 (USM!); Nevado de Coropuno, 06 May 1987, Fjeldså s.n (AAU!); Between lake Salinas and Arequipa, 3962 m, 01 February 1943, Sandeman 3816 (F!). Cusco: Ushcopata Valley, above Sicuani, 3700 m, 09 April 1913, Cook 123 (US!). Moquegua: Gral. Sanchez Cerro, Dist. Ubinas, Zona Silvestre Querapi, 3880 m, 25 January 2004, Blanchard s.n (USM!); Dist. Ubinas, Tassa, camino en Mollemoco, 3800 m, 12 July 2006, Montesinos 1185 (USM!); Ladera de Mollemoco, Tassa Dist. Ubinas, 16°11'00"S, 070°42'00"W, 3690 m, 01 June 2011, Montesinos 3175 (USM!). Mariscal Nieto, Entre Chuculay y Qda. Cuellar, 3550–3600 m, 16 December 1995, Arakaki 257 (USM!); Carumas, 16°52'18"S, 070°39'49"W, 4086 m, 09 October 2014, Boza 3010 (USM!, Z!); Torata, Quebrada Cuellar, 16°57'57"S, 070°41'02"W, 4224 m, 09 October 2014, Boza 3011 (USM!, Z!); Between Torata and Carumas, km 75–76 from Moquegua to Puno, 3600 m, 14 February 1983, Dillon 3347 (F!, MO!, US!); ca. 67 km NE of Moquegua on road to Carumas, 3680 m, 15 November 1986, Dillon 4807 (F!, USM!); Cordillera above Torata, forming grove along brook, 3900–4000 m, 14 February 1925–15 February 1925, Weberbauer 7470 (F!, US!). Torata, Ponton Cuellar, 16°59'15"S, 070°41'38"W, 3950 m, 12 April 2005, Aedo 11309 (USM!). Tacna: Candarave, Candarave, Comunidad Viltahuira, 3600 m, 25 October 2000, Cáceres 82 (USM!); Candarare, Yucamani, 3100–3400 m, 09 December 1997, La Torre 1987 (MO!, USM!); Tarata, Susapaya, 3950–4100 m, 06 December 1997, Arakaki 762 (MO!, USM!); Ticaco, 17°25'26"S, 070°03'27"W, 3458 m, 10 October 2014, Boza 3012 (USM!, Z!); Poma, 3900–4430 m, 04 December 1997, Cano 7962 (MO!, USM!); Cordillera Barroso, 4200–4580 m, 26 March 1998, Cano 8166 (MO!, USM!); 8167; 8245 (USM!); Ticaco, 3600–4000 m, 31 March 1998, Cano 8334 (USM!); Ticaco (Quebrada Ticalaco), 3300–3800 m, 16 June 1998, Cano 8420 (USM!); Cerros al SE de la Cordillera barroso, 4000–4270 m, 28 March 1998, La Torre 2153 (USM!); 4 km northeast of Tarata, 3840 m, 27 January 1952, Pearson 33 (F!); Entre Tarata y Chila, 3850 m, 31 January 1984, Rivas s.n (USM!); De Tarata a Chila, 3590 m, 01 January 1984, Rivas s.n (USM!); Bajando a Tarata, 4300 m, 06 April 1959, Vargas 12557 (CUZ!); bajando Tarata, 4300 m, 06 April 1959, Vargas 12557 (CUZ!); bajando Tarata, 3900–4100 m, 05 August 1967, Vargas 19927 (CUZ!); Candarave, 21 February 2009, Morales 1 (CUZ!); Cala-cala, 4100 m, 21 October 1976, Bernardi 16739 (F!); Pampa Arrieros Arequipa-Puno, 1901–1929, Weberbauer 4841 (B, F!, MO!).