Peru. Junín: Concepción, Dist. de Andamarca, a 2.5 km de la localidad de Alhuay, 11°41'30"S, 74°54'01"W, 4150 m, 10 Oct 2017, H.R. Quispe M. 85 (holotype: CUZ!; isotypes: USM!, Z!).

Trees 4–7 m tall. Leaves strongly congested at the branch tips, imparipinnate with 2 pairs of lateral leaflets, obtrullate in outline, (2.9)3.3–4.3 × (2.6–)3.3–4.3 cm; rachises densely sericeous, points of leaflet attachment with a tuft of long, straight hairs, sometimes with resin at leaflet insertion; stipular sheaths apically acute with spurs, densely sericeous on the outer surfaces; leaflets narrowly elliptic in outline, second pair from the terminal leaflet the largest, one of this pair (1.9)2.4–2.6 × 0.5–0.7 cm; margin entire, coriaceous, apically acute to slightly retuse, basally unequally cordate; upper leaflet surfaces almost glabrous with some hairs on the mid-veins to densely sericeous with silky hairs throughout; lower leaflet surfaces densely sericeous with silky hairs 0.6–0.9 mm long. Inflorescences pendant, 7.2–8.1 cm long, bearing 5–6(–9) flowers; floral bracts 4.5–5.6 mm long, narrowly triangular, densely sericeous on the outer surface; rachises sericeous. Flowers 7–9 mm diam.; sepals 3–4, ovate, green, densely sericeous outside; stamens 7–10, anthers orbicular, with a dense tuft of straight white hairs on the upper half; styles fimbriate, 2.7–4.4 mm long. Fruits turbinate, with variable numbers and placement of flattened spines, densely sericeous; 2.3–2.5 × 3.5–5.3 mm including spines. Diploid.

Polylepisargentea has been found in central Peru at La Mar (Ayacucho), Concepcion, Huancayo and Satipo (Junin) and La Convencion and Urubamba (Cusco) (Fig. 41). It grows mainly in humid Andean Forest at 3400–4400 m elevation. It often co-occurs with P.canoi, P.rodolfovasquezii and P.serrata (Quispe-Melgar et al. 2018) and although hybrids are not yet known, these might occur. In the Cordillera Vilcabamba, Polylepisargentea dominates the forest, with P.canoi intermixed among it and P.serrata in hilltop forest (Boyle 2001). The slightly different colours of the foliage of each species of Polylepis make this gradation obvious even from a distance (Boyle 2001).

The estimated Extent of Occurrence (EOO) for P.argentea is 23,788 km² and the Area of Occupancy is 40 km². It is known from just eight locations, but several of these encompass forests of several square kilometers. Boyle (2001) described extensive forest of this species in the remote Cordillera Vilcabamba, which is largely protected in Otishi National Park. We assess Polylepisargentea as Vulnerable (B1a+B2a).

Polylepisargentea seems morphologically closest to P.sericea and P.canoi with which it shares similar lower leaflet surface hair type and density. The most obvious differences between P.argentea and these species is leaflet size, with P.argentea having leaflets of 1.9–2.6 × 0.5–0.7 cm, whereas P.canoi has leaflets of 2.4–3.9 × 0.8–1.5 cm and P.sericea of 1.8–2.1 × 0.8–1.0 cm. Further, P.argentea has shorter hairs (0.6–0.9 mm versus 1.3–1.7 mm) than P.canoi. In P.canoi, the hairs on the lower leaflet surfaces are yellowish and often most pronounced on the secondary veins, whereas in P.argentea, they are silky and more evenly distributed. Polylepisargentea has the upper leaflet surfaces with a few hairs on mid-veins whereas P.sericea has totally glabrous upper leaflet surfaces. Additionally, the inflorescence length and number of flowers per inflorescence differ between the species, with P.argentea having inflorescences 7.2–8.1 cm long with 5–9 flowers, compared with values of 3.3–4.5 cm and 9–15 flowers in P.sericea and 8.2–14.5 cm and 12–26 flowers in P.canoi. The three species can also be distinguished by the number of stamens and style length, with P.argentea having 7–10 stamens and styles 2.7–4.4 mm long, whereas the other two species have 13–15 stamens and styles 2.4–3.8 mm in P.canoi and 1.9–2.5 mm in P.sericea.

Polylepisargentea was first collected by B. Boyle during scientific expeditions carried out in 1997 and 1998 to the isolated Cordillera Vilcabamba where he recorded three species of Polylepis (Boyle 2001). The first one, here called P.argentea, he called Polylepis sp1 and described as “a tree of 4–5 m with rather small silvery-tomentose leaflets” (specimen Boyle 4149) dominating the forest. A second species of Polylepis (here P.canoi) “with fewer, darker green and nearly glabrous leaflet”, which he called Polylepiscf.sericea (Boyle 4151), occurred patchily within stands of Polylepis sp1, as well as in monospecific stands. The third species mentioned was Polylepiscf.pauta (here P.serrata) (Boyle 4398), described as “a common tall tree (to 25 m high) in the tall hilltop forest”.

Peru. Ayacucho: La Mar, Dist. Tambo, Estera Community, sector Muyuorco, 12°54'19"S, 073°48'17"W, 3637 m, 29 June 2015, Boza 3036; 3096; 3097; 3098; 3099; 3100; 3101; 3102; 3103; 3104; 3105; 3106 (USM!, Z!). Cusco: La Convención, Dist. Huayopata Abra Málaga, 13°08'05"S, 072°19'18"W, 3802 m, 13 June 2015, Boza 3032; 3082; 3083; 3084 (USM!, Z!); Cuzco. Provincia La Convención, Bosque Qulcamachay, 4200 m, 01 October 2002, Palomino 2030 (QCA!); Dist. Huayopata, localidad Panticalle, Abra Málaga, 13°08'02"S, 072°19'32"W, 3725 m, 30 May 2006, Toivonen 84; 85; 86; 87 (CUZ!). Urubamba, Inkatambo, 13°18'06"S, 072°31'44"W, 4340 m, 01 September 2002, Arce s.n (USM!); Qésqa, 13°17'51"S, 072°24'57"W, 4000 m, 01 October 2002, Arce s.n (USM!); Abra Málaga, 13°08'43"S, 072°18'09"W, 4318 m, 01 October 2002, Arce s.n (CUZ!); Inkatambo 13°18'06"S, 072°31'44"W, 3840 m, 01 September 2002, Arce s.n (CUZ!); Dist. Ollantaytambo, Huaytampo, 13°10'47"S, 072°21'10"W, 3650 m, 07 November 2002, Calatayud 1035 (CUZ!, F!, MO!, USM!); Santuario Histórico Machu Pichu, camino Inca, Km 88–112, por puente Ruinas, 13°18'S, 072°07'W, 2000–4100 m, 20–21 June 1988, Núñez 9204 (MO!); Dist. Ollantaytambo, localidad Abra Málaga, 13°09'02"S, 072°18'09"W, 4230 m, 29 May 2006, Toivonen 15 (CUZ!); 16 (CUZ!); Dist. Ollantaytambo, localidad Huaytampo, 13°10'31"S, 072°21'03"W, 3800 m, 06 July 2006, Toivonen 95 (CUZ!); 96 (CUZ!). Junín: Concepcion, Andamarca, 11°41'30"S, 074°54'01"W, 2300 m, 14 June 2002, Martinez 18 (USM!); Dist. de Andamarca, a 2.5 km de la localidad de Alhuanay, 11°41'30"S, 074°54'01"W, 4150 m, 10 October 2017, Quispe 85 (CUZ!, USM!, Z!). Huancayo, Dist. de Santo Domingo de Acobamba, a 5 km de la localidad de Callanca, 11°45'43"S, 074°55'15"W, 4200 m, 12 October 2017, Quispe 87 (CUZ!, USM!, Z!). Satipo, Satipo/La Convencion Cordillera Vilcabamba Río Ene slope, near summit of divide, 11°39'30"S, 073°40'02"W, 3350 m, 07 June 1997, Boyle 4149 (USM!).