This species differs from Polylepislanata (Kuntze) M.Kessler & Schmidt-Leb. in having slightly narrower leaflets, crenate leaflet margins with more teeth per side, shorter inflorescences with more stamens and longer styles. Further, it also has a distinct geographical distribution with a very different climatic niche.

Peru. Cusco: Urubamba, Mantanay, 13°12'03"S, 072°09'20"W, 3350–3800 m, 7 Sep 2002, J. Farfan et al. 281 (holotype: CUZ!; isotypes: AMAZ, HUT, MO!, USM!).

Trees 4–20 m tall. Leaves slightly congested at the branch tips, imparipinnate with 2–3 pair of leaflets, obtrullate in outline, (4.1–)5.1–7.1 × 2.0–4.9 cm; rachises densely lanate, points of leaflet attachment with a tuft of long hairs; stipular sheaths apically truncate, densely lanate on the outer surfaces; leaflets obovate in outline, second pair from the terminal leaflet the largest, one of this pair 1.6–2.6 × 0.6–1.1 cm; margin crenate with 6–11 teeth, apically emarginate, basally unequally cordate; upper leaflet surfaces sparsely lanate; lower leaflet surfaces densely lanate with whitish hairs 1.3–1.5 mm long. Inflorescences pendant, 5.0–8.8 cm long, bearing 5–11 flowers; floral bracts 5.0–7.5 mm long, narrowly triangular, densely lanate on the outer surface; rachises glabrous to villous. Flowers 8.2–11.0 mm diam.; sepals 4, ovate, green, densely lanate outside; stamens 23–27, anthers orbicular, with a dense tuft of straight white hairs on the upper half; styles fimbriate, 3.3–4.1 mm long. Fruits turbinate, with 2–3 irregular flattened ridges with a series of spines, densely pilose; (7.3–)10.3–15.1 × 6.0–8.2 mm including spines. Octoploid, perhaps also tetraploid.

Polylepissacra is distributed from central Peru in Huarochiri (Lima) and northern Junín to southern Peru in Abancay (Apurimac) and Cusco (Fig. 92). The species occurs in relatively dry valleys at 3300–4600 m elevation. It often co-occurs with P.subsericans and P.rodolfovasquezii in the Vilcanota Mountain range (Cusco), but generally occurs at lower elevations than these two species. At 4300 m elevation, a stand of P.sacra had a mean maximum tree height of 18.5 m, whereas a stand at 3980 m was only 15.9 m tall, presumably because of drier conditions in the arid valley bottom (Kessler et al. 2014). Average morphological and physiological features of P.sacra estimated at Vilcanota are a leaf area of 6.27 cm², specific leaf area of 81.20 cm² g^-1, leaf thickness of 396.84 μm, epidermal cell length of 33.58 μm, chlorophyll parenchyma cell length of 95.77 μm, 11.02 stomata/mm², rhytidome thickness of 3.75 mm, water content of 16.3%, relative water content of 77.6% and water saturation deficit of 22.1% (Arroyo 2015, as P.racemosa). The Cordillera Vilcanota has a high floristic diversity with over 144 plant species (Servat et al. 2002). The Polylepis forests in the region hold up to 60 species of birds (Yanacocha) (Servat et al. 2002) with a high number of endemic bird species (Fjeldså et al. 1999; Fjeldså 2002a) including the endangered species Cinclodesexcelsior, Anairetesalpinus and Leptasthenuraxenothorax and the near-threatened species Leptasthenurayanacencis, Asthenesurubambensis, Conirostrumbinghami (= Oreomanesfraseri) and Xenodacnisparina (Servat et al. 2002).

We name this species after the Sacred Valley of the Incas stretching from Pisac to Ollantaytambo in Cusco (Peru) where the species is well distributed.

The EOO for Polylepissacra is estimated as 62,397 km², the AOO is assessed at 120 km² and it is known from 15 locations. In Cusco, it is protected within the Private Conservation Areas Network of the Vilcanota Mountain range. It has been subject to reforestation activities since 2001 by ECOAN, a non-profit NGO dedicated to the conservation of endangered species and threatened Andean ecosystems. However, at many of its locations, the species grows in habitats that are strongly affected by human activities including grazing and burning. We assess P.sacra as Vulnerable (B1a+B2a).

The taxonomic status of Peruvian populations of Polylepis from the Sacred Valley (also known as Vilcanota Valley) related to P.racemosa has long been confused. These plants have previously been identified as P.racemosa (Simpson 1979; Lloyd 2008a, b; Lloyd and Marsden 2008) or as P.lanata (Mendoza and Cano 2012). However, Simpson (1979) already pointed out that collections from Lima (Killip & Smith 21745, Asplund 11374) with more than one pair of large leaflets and longer inflorescences with numerous flowers are a morphologically extreme type of P.racemosa as defined by her. We consider that the recognition of P.sacra as a distinct species is justified, based on morphological, ecological and geographical grounds. Polylepissacra resembles P.lanata in having 2–3 lateral leaflet pairs, lanate hairs and relatively long inflorescences. However, it has narrower leaflets with crenate margins with more teeth per side (0.6–1.1 cm with 6–11 teeth versus 0.9–1.4 cm with 5–9 teeth), shorter inflorescences (5.0–8.8 cm versus (5.0–)6.1–12.3 cm), more stamens per flower (23–27 versus 15–19) and longer styles (3.3–4.1 versus 2.5–3.2 mm).

Peru. Apurimac: Abancay, Bosque de Balcon, 4200 m, 16 June 2004, Palomino 3924 (QCA!). Cusco: Anta, Anta, 13°28'17"S, 072°08'23"W, 3546 m, 01 March 2003, Arce s.n (USM!); Pucaccacca, 13°29'21"S, 072°07'59"W, 3635 m, 01 March 2003, Arce s.n (USM!); Santa Ana, El Chaccan, 3500 m, 16 November 1972, Brunel 37 (MO!); Santa Ana, El Chaccan. Sub-xerofito, micro-thermico, 3490 m, 05 March 1973, Brunel 596 (MO!). Calca, Arin North of Cusco, road Cusco-Urubamba, 13°20'S, 072°01'W, 2897 m, 20 July 1992, Chávez 807 (CUZ!); Calca, the SW facing slopes found to the immediate E of the prominent tower known by locals as “Kontorqayku” 5 km NE of Huarán, 13°16'05"S, 072°01'08"W, 4245 m, 06 May 2011, Sylvester 1196 (CUZ!, Z!); Calca, the SW facing slopes found to the immediate E of the prominent tower known by locals as “Kontorqayku” 5 km NE of Huarán, 13°16'06"S, 072°01'08"W, 4250 m, 07 May 2011, Sylvester 1213 (CUZ!, Z!); Calca, the SW facing slopes found to the immediate E of the prominent tower known by locals as “Kontorqayku” 5 km NE of Huarán, 13°16'11"S, 072°01'06"W, 4230 m, 09 May 2011, Sylvester 1223 (CUZ!, Z!); Calca, the SW facing slopes found to the immediate E of the prominent tower known by locals as “Kontorqayku” 5 km NE of Huarán, 13°16'13"S, 072°01'05"W, 4243 m, 10 May 2011, Sylvester 1228 (CUZ!, Z!); Calca, the SW facing slopes found to the immediate E of the prominent tower known by locals as “Kontorqayku” 5 km NE of Huarán, 13°16'10"S, 072°01'07"W, 4237 m, 25 May 2011, Sylvester 1230 (CUZ!, Z!); Calca, the SW facing slopes found to the immediate E of the prominent tower known by locals as “Kontorqayku” 5 km NE of Huarán, 13°16'05"S, 072°01'16"W, 4387 m, 25 May 2011, Sylvester 1260 (CUZ!, Z!); Calca, top of the prominent tower known by locals as “Kontorqayku” 5 km NE of Huarán, 13°16'05"S, 072°01'16"W, 4395 m, 16 May 2011, Sylvester 1262 (CUZ!, Z!); Calca, the SW facing slopes found 700 m E of the prominent tower known by locals as “Kontorqayku” 5 km NE of Huarán, 13°16'16"S, 072°01'05"W, 4242 m, 16 May 2011, Sylvester 1270 (CUZ!, Z!); Calca, top of the prominent tower known by locals as “Kontorqayku” 5 km NE of Huarán, 13°16'09"S, 072°01'07"W, 4243 m, 16 May 2011, Sylvester 1278 (CUZ!, Z!); Calca top of the prominent tower known by locals as “Kontorqayku” 5 km NE of Huarán, 13°16'10"S, 072°01'16"W, 4261 m, 16 May 2011, Sylvester 1281 (CUZ!, Z!); Calca, top of the prominent tower known by locals as “Kontorqayku” 5 km NE of Huarán, 13°16'06"S, 072°01'16"W, 4405 m, 17 May 2011, Sylvester 1288 (CUZ!, Z!); Calca, the SW facing slopes found to the immediate E of the prominent tower known by locals as “Kontorqayku” 5 km NE of Huarán, 13°16'14"S, 072°01'04"W, 4258 m, 25 May 2011, Sylvester 1310 (CUZ!, Z!); Calca, top of the prominent tower known by locals as “Kontorqayku” 5 km NE of Huarán, 13°16'06"S, 072°01'17"W, 4403 m, 25 May 2011, Sylvester 1318 (CUZ!, Z!); Calca, the grassy grazed land found to the immediate E of the prominent tower known by locals as “Kontorqayku” 5 km NE of Huarán, 13°16'09"S, 072°01'06"W, 4247 m, 25 May 2011, Sylvester 1338 (CUZ!, Z!); Calca, the grassy grazed land found to the immediate E of the prominent tower known by locals as “Kontorqayku” 5 km NE of Huarán, 13°16'05"S, 072°01'03"W, 4297 m, 25 May 2011, Sylvester 1339 (CUZ!, Z!); Calca, the grassy grazed land found to the immediate E of the prominent tower known by locals as “Kontorqayku” 5 km NE of Huarán, 13°16'05"S, 072°01'03"W, 4297 m, 25 May 2011, Sylvester 1340 (CUZ!, Z!); Calca, the SW facing slopes found to the immediate E of the prominent tower known by locals as “Kontorqayku” 5 km NE of Huarán, 13°16'03"S, 072°01'02"W, 4310 m, 02 June 2011, Sylvester 1342 (CUZ!, Z!); Calca, the SW facing slopes found to the immediate E of the prominent tower known by locals as “Kontorqayku” 5 km NE of Huarán, 13°16'04"S, 072°01'04"W, 4295 m, 02 June 2011, Sylvester 1343 (CUZ!, Z!); Calca, Surayoc, in the deep forested valley 2 km NE of the small settlement of Churo and 6 km NE of Huarán, 13°15'44"S, 072°59'50"W, 4354 m, 17 July 2011, Sylvester 1351 (CUZ!, Z!); 1352 (CUZ!, Z!); Surayoc, in the deep forested valley 2 km NE of the small settlement of Churo and 6 km NE of Huarán, 13°15'47"S, 071°59'49"W, 4071 m, 25 May 2011, Sylvester 1403 (CUZ!, Z!); 1406 (CUZ!, Z!); Calca, the SW facing slopes found to the immediate E of the prominent tower known by locals as “Kontorqayku” 5 km NE of Huarán, 13°16'09"S, 072°01'06"W, 4253 m, 25 May 2011, Sylvester 1684 (CUZ!, Z!); Calca, top of the prominent tower known by locals as “Kontorqayku” 5 km NE of Huarán, 13°16'05"S, 072°01'00"W, 4319 m, 07 June 2012, Sylvester 1686; 1687 (CUZ!, Z!); Calca along track from Huaran to Cancha Cancha, 3.5 km north of Huaran, 13°16'38"S, 072°01'44"W, 3377 m, 22 June 2013, Sylvester 2236 (Z!, LPB). Cusco, Sacsayhuaman, 13°30'35"S, 071°58'43"W, 3391 m, 17 June 2015, Boza & Urquiaga 3081 (CUZ!, USM!, Z!); San Jerónimo, Hauccoto, Pachatusan, 13°31'02"S, 071°48'39"W, 4400 m, 23 October 2004, Galiano 6980 (AMAZ, CUZ!, F!, HUT, MO!, MOL, USM!). Espinar, Yauri, localidad Virginniyoc, 4100 m, 13 April 1987, Núñez 7889B (CUZ!). Urubamba, Chicón, 13°15'01"S, 072°05'16"W, 3517 m, 01 April 2003, Arce s.n (CUZ!, USM!); Yanahuara, Mantanay, 13°12'51"S, 072°09'46"W, 4078 m, 17 June 2015, Boza & Urquiaga 3034; 3090; 3091 (CUZ!, USM!, Z!); above Urubamba, Chicon Valley below Nevado Chaiñapuerto, 13°15'S, 072°05'W, 3370–3550 m, 22 March 1987, Brandbyge 456 (AAU!); Urubamba, Mantanay, 13°12'03"S, 072°09'20"W, 3350–3800 m, 07 September 2002, Farfán 281 (CUZ!, F!, HUT, MO!, USM!); Urubamba, Pumahuanca, 13°12'36"S, 072°05'56"W, 3300–3850 m, 09 September 2002, Farfán 341 (AMAZ, CUZ!, F!, HUT, MO!, MOL, USM!); Huaran ca. Yanachoca, 13°21'S, 072°03'W, 3000–4000 m, 26 January 1991, Núñez 12568; 12655 (CUZ!, MO!); Huayoccari to Yanacocha, Urubamba, NW from Cusco, 13°16'S, 072°04'W, 14 February 1987, Núñez 6999; 7066 (MO!); desde Huayocri hasta Yanacocha, cerca a Huayllabamba, 13°21'S, 072°03'W, 3000–3890 m, 25 June 1988, Núñez 9222 (CUZ!, MO!); Pumahuanca, bosque de Queñaquenco-Cuyo, 4100 m, 16 June 2004, Palomino 4809 (QCA!); Urubamba, 1.5 km 100 NE up the valley from the Munaycha college, 5 km North upvalley from Urubamba, 13°14'39"S, 072°04'46"W, 3865 m, 25 May 2011, Sylvester 1349; 1350 (CUZ!, Z!); Huayllabamba, grazed slope situated on the N side of Laguna Qellococha 500 m further N passing through the Polylepis forest 5 km N of Huayocari Village, 13°16'42"S, 072°03'00"W, 4168 m, 28 February 2011, Sylvester 604; 637; 643; 644 (CUZ!, Z!); Huayllabamba, grazed slope situated on the N side of Laguna Qellococha 500 m further N passing through the Polylepis forest 5 km N of Huayocari Village, 13°16'43"S, 072°02'56"W, 4182 m, 11 March 2011, Sylvester 700; 725 (CUZ!, Z!); Huayllabamba, grazed slope situated on the N side of Laguna Qellococha 500 m further N passing through tha Polylepis forest 5 km N of Huayocari Village, 13°16'43"S, 072°03'00"W, 4162 m, 12 March 2011, Sylvester 732 (CUZ!, Z!); Huayllabamba, grazed slope situated on the N side of Laguna Qellococha 500 m further N passing through tha Polylepis forest 5 km N of Huayocari Village, 13°16'36"S, 072°03'03"W, 4199 m, 13 March 2011, Sylvester 755 (CUZ!, Z!); Huayllabamba, grazed slope situated on the N side of Laguna Qellococha 500 m further N passing through tha Polylepis forest 5 km N of Huayocari Village, 13°16'42"S, 072°03'07"W, 4163 m, 13 March 2011, Sylvester 764 (CUZ!, Z!); Huayllabamba, grazed slope situated on the N side of Laguna Qellococha 500 m further N passing through tha Polylepis forest 5 km N of Huayocari Village, 13°16'42"S, 072°03'07"W, 4229 m, 14 March 2011, Sylvester 765; 773 (CUZ!, Z!); Huayllabamba, grazed slope situated on the N side of Laguna Qellococha 500 m further N passing through tha Polylepis forest 5 km N of Huayocari Village, 13°16'42"S, 072°03'07"W, 4215 m, 14 March 2011, Sylvester 781 (Z!); Huayllabamba, grazed land situated on the S side of Laguna Qellococha 5 km N of Huayocari Village 55 m S of Laguna Qellococha, 13°16'42"S, 072°03'01"W, 4151 m, 15 March 2011, Sylvester 789 (Z!); 796 (Z!); Huayllabamba, Yanacocha, 13°17'12"S, 072°03'06"W, 3760 m, 07 June 2006, Toivonen 43; 44; 45 (CUZ!); Huayllabamba, Yanacocha, 13°16'49"S, 072°59'06"W, 3960 m, 07 June 2006, Toivonen 47; 48 (CUZ!); Mantanay, 13°12'07"S, 072°09'32"W, 4100 m, 19 July 2007, Toivonen 5; 6; 7; 8 (CUZ!); Huayllabamba, Yanacocha, 13°16'55"S, 072°03'00"W, 3950 m, 16 June 2006, Toivonen 50; 51 (CUZ!); Huayllabamba, Qelloqocha, 13°16'52"S, 072°03'07"W, 4180 m, 31 August 2006, Toivonen 53; 54; 55; 56 (CUZ!); Urubamba, Pumahuanca, 13°12'30"S, 072°05'53"W, 4150 m, 13 June 2006, Toivonen 59 (CUZ!); Urubamba, Pumahuanca, 13°12'43"S, 072°05'51"W, 4140 m, 25 May 2006, Toivonen 61 (CUZ!). Huayllabamba, entre quebrada de Huayaccari y las lagunas de Yanacocha y Kellococha parte alta y media, 13°21'15"S, 072°03'55"W, 3400–4200 m, 17–18 May 1989, Tupayachi 1044 (MO!); entre la quebrada de Huayoccari y las lagunas de Yanacocha y Kellococha, hacia las laderas Sureste de las lagunas, 13°19'00"S, 072°02'00"W, 2900–3600 m, 19–23 June 1989, Tupayachi 1092 (GH!, MO!); Huayllabamba, entre Huayoccari y las lagunas de Yanacocha y Kellococha, 13°13'S, 072°16'W, 2900–4600 m, 17–18 July 1989, Tupayachi 1130 (MO!); 1138 (MO!); Huayllabamba, Lagunas Yanachocha y Quellococha hacia San Juan, NE de Cusco, 13°16'S, 072°04'W, 2900–4600 m, 19 August 1989, Tupayachi 1212A (MO!); 1213 (MO!); Huayllabamba, Huayaccari-Yanaccocha; camino a Yanaccocha, 13°21'S, 072°03'W, 3000–4200 m, 03 March 1986, Tupayachi 137 (CUZ!, MO!); Huayllabamba. Laguna Yanaccocha y Kello ccocha, 13°21'15"S, 072°03'55"W, 3800–4200 m, 07 January 1989, Tupayachi 854 (MO!); Huayllabamba, entre la quebrada Huayoccari, Lagunas de Yanacocha y Kellococha, 13°21'15"S, 072°03'55"W, 2900–3860 m, 12 February 1989, Tupayachi 896 (MO!); Urubamba, Pumahuanca, 13°14'35"S, 072°06'50"W, 3543 m, 20 February 2006, Valenzuela 6154 (AMAZ, CUZ!, HUT, MO!, USM!); Pumahuanca, 3450–3850 m, 25 October 1952, Vargas 10799 (CUZ!); Quebrada Chicon, 3000 m, 14 August 1974, Vargas 22604 (CUZ!); Sutocc to Pacchacc, 3500–3650 m, 15 November 1962, Vargas 7855 (CUZ!); Yanahuara, 3600 m, 16 March 1950, Vargas 9315 (CUZ!). Junín: Jauja, Llocllapampa, 3350 m, Rosales 4 (USM!). Lago Chinchay Cocha Junin, Ondores, 11°04'S, 076°08'W, 4000 m, 05 February 1987, Boertmann 17a (AAU!). Llocllapampa, Parco entre Jauja y Oroya, 3200–3300 m, 24 November 1947, Ferreyra 2833 (MO!, USM!). Tarma, Ayabamba, 27 April 1905, Soukup 2536 (F!). Lima: Huarochiri, Vista Alegre, Río Blanco, 3923 m, 21 February 1990, Arce 205 (MO!); 3400 m, 03 June 1940, Asplund 11343 (US!); 3700 m, 04 June 1940, Asplund 11374 (US!). San Mateo, Río Blanco; open hillside, 3000–3500 m, 15–17 April 1929, Killip 21745 (A!, F!, US!).