Peru. Ayacucho: Hacienda Tortorabamba, 3500–3600 m, May 1910, Weberbauer 5487 (holotype: F!; isotypes: F!, G!)

Trees 3–10 m tall. Leaves slightly congested at the branch tips, imparipinnate with one pair of leaflets, obtrullate in outline, (1.7–)2.8–3.4 × 1.7–2.5 cm; rachises densely pilose, points of leaflet attachment with a tuft of long hairs; stipular sheaths apically acute with spurs, densely strigose on the outer surfaces; leaflets narrowly elliptic in outline, second pair from the terminal leaflet the largest, one of this pair (1.3–)1.7–2.8 × 0.5–0.7 cm; margin entire to slightly serrate at apex with 3–4 teeth, apically round or emarginate with the trichomes from the lower surface projecting into the notch, basally unequally cordate; upper leaflet surfaces sparsely strigose; lower leaflet surfaces densely strigose with yellowish hairs 0.7–1.2 mm long. Inflorescences pendant, (1.9–)2.5–4.9(–5.6) cm long, bearing 3–4(–6) flowers; floral bracts 3.2–6.6 mm long, narrowly triangular, densely pilose on the outer surface; rachises pilose. Flowers 7.7–9.6 mm diam.; sepals 4, ovate, green, densely pilose outside; stamens 9–13, anthers orbicular, with a dense tuft of straight white hairs on the upper half; styles fimbriate, 2.0–4.2 mm long. Fruits turbinate, with 3–4 irregular flattened ridges with a series of spines, densely pilose; 7.5–9.1 × 4.3–5.9 mm including spines. Tetraploid.

Polylepissubericans is distributed in the high mountains of southern Peru from Huaytará (Huancavelica) to (Urubamba) Cusco (Fig. 73). The species occurs in relatively dry and cold areas at 3760–4800(–5100) m elevation. Human activities cause variation of the forest structure, with forest in dry areas being more strongly degraded (Toivonen et al. 2011). During the rainy season, P.subsericans shows a positive correlation between temperature and tree-ring growth, pointing out the importance of temperature for its growth (Jomelli et al. 2012). Polylepissubsericans is amongst the highest-growing tree species in the world and in Vilcanota (Cusco), forests of P.subsericans reach mean maximum tree heights of 13 m at 4650 m (Kessler et al. 2014). These stands grow under mean growing season air temperatures of 3.8 °C and mean growing season soil temperatures of 4.6 °C. Polylepissubericans is adapted to high elevations and, relative to other species of Polylepis, has low levels of stomatal conductance and high levels of quantum use efficiency (Toivonen et al. 2014). The anatomical traits of the species have been studied in depth by Arroyo (2015). Stands of P.subsericans in the Vilcanota Mountains host a moderate diversity of plants (144 spp.) and specialist bird species (30 spp.) (Servat et al. 2002). Among the endemic birds, Leptasthenuraxenothorax, Cinclodesexcelsior and Anairetesalpinus are threatened by habitat reduction, making this habitat a priority for conservation (Fjeldså 1987; Fjeldså and Kessler 1996; Cardenas-Villavicencio and Arque 2010).

The EOO for Polylepissubsericans is estimated as 15,223 km², the AOO is assessed at 84 km² and it is known from 11 locations. It has been categorized as EN (B1b(iii)) (Mendoza and León 2006; SERFOR 2006). In Cusco, it is protected within the Private Conservation Areas Network of the Vilcanota Mountain range. Since 2001, it has been subject to reforestation activities by ECOAN, a non-profit NGO dedicated to the conservation of endangered species and threatened Andean ecosystems. However, populations from Ayacucho have high anthropogenic impact from the surrounding communities to the point of almost disappearing completely (Mendoza and Roque 2007). We assess P.subsericans as Vulnerable (B1a+B2a).

Polylepissubsericans may be confused with P.rodolfovasquezii, with which it hybridizes. They share the lateral leaflet pair number and more or less same leaflet hair length. Polylepissubsericans differs by having leaflets (1.3–)1.7–2.8 cm long, strigose hairs and longer inflorescences (1.9–5.6 cm) with 3–6 flowers, whereas P.rodolfovasquezii has leaflets 0.9–1.1 cm long, sericeous hairs and inflorescences 0.9–1.1 cm long with just one flower. For additional morphological similarities, see under P.flavipila and P.pilosissima.

Peru. Apurimac: Abancay, Bosque de Runtococha, 4150 m, 08 April 2003, Palomino 3964 (QCA!). Ayacucho: Huamanga, Torobamba, 3500–3600 m, 01 May 1910, Weberbauer 5487 (F!). La Mar, Laguna de Toctococha, 12°57'39"S, 074°05'57"W, 4200 m, 30 September 2003, Mendoza 1013 (MO!). Cusco: Calca, Sacsamonte-Huarán, 13°12'58"S, 072°02'05"W, 4340 m, 01 May 2003, Arce s.n (USM!); Lares, Quishuarani, 13°08'34"S, 072°02'31"W, 4281 m, 17 January 2014, Boza 3000 (USM!, Z!); 3121 (USM!, Z!); Bosque de Polylepis de Yanacocha, 13°16'59"S, 072°03'02"W, 4012 m, 17 August 1998, Mendoza 112 (CUZ!); Dist. Calca, ledge situated on the prominent cliff 1.5 km South (170) of Cancha Cancha Village Huaran, 13°14'37"S, 072°01'14"W, 4545 m, 27 March 2011, Sylvester 1013; 1025; 1027 (CUZ!, Z!); Dist. Calca, top of the prominent tower known by locals as “Kontorqayku” 5 km NE of Huaran, 13°16'06"S, 072°01'16"W, 4398 m, 17 May 2011, Sylvester 1287 (CUZ!, Z!); on the SW corner of the topmost part of tower, 13°16'06"S, 072°01'16"W, 4410 m, 17 May 2011, Sylvester 1328; 1329; 1344 (CUZ!, Z!); Dist. Calca, the eastern side of the valley 7.2 km 10 N from Huaran, 13°15'06"S, 072°00'57"W, 4649 m, 18 July 2011, Sylvester 1354; 1355; 1359 (CUZ!, Z!); Dist. Calca, upper Potreros forest, on the N facing mountainside above the main Potreros forest. 4 km SW of Cancha Cancha Village, Huaran, 13°15'46"S, 072°02'51"W, 4726 m, 18 July 2011, Sylvester 1361; 1362; 1364; 1365 (CUZ!, Z!); Dist. de Calca, the Wakapacana forest, on the eastern side of the Valley 7.2 km 10 N from Huaran, 13°15'05"S, 072°00'56"W, 4637 m, 26 March 2012, Sylvester 1408; 1413 (CUZ!, LPB, Z!); Dist. Calca, within the SW facing forest at the top of the prominent tower known by local as “Kontorqayku” 5 km NE of Huaran, 13°16'07"S, 072°01'17"W, 4388 m, 11 June 2012, Sylvester 1630; 1690 (CUZ!, Z!); Prominent ledge situated on the prominent SW facing cliff face 1.5 km South (170) of Cancha Cancha Village Huaran, 13°14'34"S, 072°01'14"W, 4517 m, 09 March 2011, Sylvester 804; 809; 813; 820; 868; 875; 876; 880; 881 (CUZ!, Z!); Dist. Calca. Ledge situated on the prominent cliff 1 km South (150) of Cancha Cancha Village Huaran, 13°14'35"S, 072°01'14"W, 4500 m, 27 March 2011, Sylvester 937; 947; 948; 973; 975; 977 (CUZ!, Z!). La Convención, Ccayara 18L 718405/ UTM 8540752, 4416 m, 01 August 2002, Arce s.n (CUZ!, USM!). Urubamba, Yanahuara, Mantanay, 13°11'57"S, 072°09'33"W, 4330 m, 17 June 2015, Boza 3033; 3085; 3086; 3087; 3088; 3089 (USM!, Z!); Dist. Urubamba, ACP Mantanay, 10 km up the valley from Yanahuara, by the side of Laguna Manalloqsa, in the small valley 3 km East of Laguna Ipsaycocha, 13°12'01"S, 072°08'42"W, 4640 m, 24 June 2012, Sylvester 1714 (Z!); 13°12'02"S, 072°08'46"W, 4638 m, 03 February 2011, Sylvester 405; 408; 512 (CUZ!, Z!); Dist. Urubamba, ACP Mantanay 10 km up the valley from Yanahuara, by the side of Laguna Manalloqsa, in the small valley 3 km of Laguna Ipsacocha, 13°12'08"S, 072°08'44"W, 4806 m, 03 February 2011, Sylvester 518; 531; 536; 544; 575; 576; 585 (CUZ!, Z!); Dist. Huayllabamba, terrace situated on the N side of Laguna Qellococha and to the E of the waterfall 5 km N of Huayocari Village, 13°16'34"S, 072°03'09"W, 4343 m, 10 March 2011, Sylvester 642; 671; 679 (CUZ!, Z!); 13°16'35"S, 072°03'01"W, 4227 m, 09 March 2011, Sylvester 684; 686; 688; 691 (CUZ!, Z!); 13°16'35"S, 072°03'03"W, 4226 m, 10 March 2011, Sylvester 695; 740 (CUZ!, Z!); Dist. de Huayllabamba. 5 km N of Huayocari village, 800 m NW of Laguna Qellococha along the path leading to higher lake, 13°16'32"S, 072°03'10"W, 4366 m, 10 March 2011, Sylvester 741; 742; 749; 751 (CUZ!, Z!); Mantanay, 13°11'08"S, 072°09'20"W, 4370 m, 19 July 2006, Toivonen 11; 12 (CUZ!); Dist. Huayllabamba, localidad Qelloqocha, 13°16'16"S, 072°03'09"W, 4350 m, 19 July 2006, Toivonen 38; 39; 40; 65 (CUZ!); Dist. Huayllabamba, entre Huayoccari y las lagunas de Yanacocha y Kellococha, 2900–4600 m, 17–18 July 1989, Tupayachi 1137 (MO!); 1140 (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 1192; 1212 (MO!); Localidad Yucay-Puyuc-Hueskana, 4200 m, 24 April 1993, Tupayachi 2259 (CUZ!); Localidad Parte alta de Cuyuc, 4200 m, 28 May 1994, Tupayachi 2554 (CUZ!); Pumahuanca, Bosque de Quenñaquemocuyo, 4400 m, 18 June 2004, Tupayachi 4808 (QCA!); Dist. Huayllabamba, Laguna Yanaccocha y Kello ccocha, 13°21'15"S, 072°03'55"W, 3800–4200 m, 07 January 1989, Tupayachi 859 (MO!); Localidad Mantanay, 13°12'02"S, 072°08'57"W, 4526 m, 01 May 2003, Arce s.n (CUZ!).