Peru. Huanuco: Huamalics, southeast of Monzon, 3400–3500 m, 1903, Weberbauer 3354 (holotype: B destroyed; photos at MO!, US).

Trees 3–27 m tall. Leaves slightly congested at the branch tips, imparipinnate with 4–7 pairs of lateral leaflets, obtrullate in outline, (5.4–)6.7–8.7(–11.1) × (3.2–)3.9–5.7(–6.4) cm; rachises densely tomentose; points of leaflet attachment with a ring of short tomentose hairs around; stipular sheaths apically acute with spurs, densely lanate on the outer surfaces; leaflets elliptic in outline, second pair from the terminal leaflet the largest, one of this pair (1.8–)2.4–3.5 × 0.8–1.0(–1.2) cm; margin serrate with 4–5 teeth, apically acute, basally unequally cordate; upper leaflet surfaces glabrous or sparsely lanate mainly in the mid-vein depression; lower leaflet surfaces densely lanate with whitish hairs 0.7–1.2 mm long. Inflorescences pendant, (7.6–)9.5–13.3(–17.3) cm long, bearing 16–35 flowers; floral bracts 3.4–4.5 mm long, narrowly triangular, densely villous on the outer surface; rachises villous. Flowers 5.2–5.9 mm diam.; sepals 4, ovate, green, densely sericeous outside; stamens (4–)6–14, anthers orbicular, with a dense tuft of straight white hairs on the upper half; styles fimbriate, 1.2–2.3 mm long. Fruits turbinate, with variable numbers and placement of thin spines, densely villous; (3.8–)6.1–6.7 × 5.6–8.8 mm including spines. Diploid.

Polylepisserrata is distributed from San Martín to Cusco, Peru (Fig. 24), where it occurs at 2000–3950 m elevation. It grows in relatively wet habitats usually mixed with or at the upper edge of the montane cloud forest, commonly with species of the genera Oreopanax and Weinmannia (Young 1993). It often also co-occurs with P.canoi and towards its upper distribution grades into forests of P.rodolfovasquezii (Boyle 2001; Kessler et al. 2014). This is one of the tallest Polylepis species, with heights of up to 27 m and diameters of up to 80 cm recorded (Toivonen et al. 2011). In a study in Cuzco, Peru, vegetative reproduction was found to be absent at 3000 m, but increased to around 80% at 3500–3800 m (Toivonen et al. 2011). Based on pollen records, Polylepis of presumably this species was common at Laguna de Chochos in San Martín, Peru, at the beginning of the Holocene some 10,000–6,000 bp and later declined (Bush et al. 2005). The ecophysiology of this species has been studied by Toivonen et al. (2014; as P.pauta).

The EOO for Polylepisserrata is estimated as 68,454 km², the AOO is assessed at 100 km² and it occurs at 18 locations. In Peru, was categorized as Near Threatened (SERFOR 2006, as P.pauta). It is restricted to small areas of eastern Peru where it is protected within Río Abiseo and Manu National Parks. However, the habitat of P.serrata is threatened by fires and forest destruction. We assess this species as Vulnerable (B1a+B2a, C1).

This species is quite similar to P.pauta and, in fact, it was treated as a junior synonym by Simpson (1979). Nevertheless, Simpson already pointed out the morphological diagnosability of geographical populations of P.pauta as defined by her. We consider that the recognition of P.serrata is justified, based on morphological, ecological and geographical grounds, and suggest that this taxon should be re-instated at species level. Polylepisserrata differs from P.pauta by having longer leaflets (1.8–3.5 cm versus 1.7–2.2 cm long) with different type and relatively shorter hairs (0.7–1.2 mm, lanate versus 0.9–1.9 mm, sericeous). Polylepisserrata further has shorter styles (1.2–2.3 mm; P.pauta: 2.3–2.5 mm).

Polylepisserrata also is morphologically similar to P.ochreata, with which it shares the number of leaflets (4–7 pairs). The most obvious differences between P.serrata and this species are the leaflet width, margin, apex and hair type and length, with P.serrata having elliptic leaflets 0.8–1.2 cm long, with acute apex and longer lanate hairs (0.7–1.2 mm) on the lower surface, whereas P.ochreata has narrowly elliptic leaflets 0.5–0.7 cm long, emarginate apex and short sericeous hairs (0.3–0.5 mm) on the lower surface.

Peru. Cusco: Calca, Lares Cuncani, 07 June 1991, Tupayachi 1505 (CUZ!). La Convención, Prov. Machupicchu, Chakimayu, 3235 m, 01 September 2002, Arce s.n (CUZ!, USM!); Batiyayoc 13°08'01"S, 072°19'45"W, 3705 m, 01 October 2002, Arce s.n (CUZ!); Dist. Santa Teresa, Uchuyillaspay, 13°07'23"S, 072°37'30"W, 3883 m, 22 September 2005, Huamantupa 7018 (CUZ!, MO!); Dist. Echarate, Huayopata, San Luis, 13°04'43"S, 072°23'25"W, 2800 m, 30 March 2006, Huamantupa 7526 (CUZ!, MO!, USM!); Potrero, Bosque de Ukumuriyoc, 3600 m, 01 October 2002, Palomino 1737 (QCA!); Dist. Huayopata, Panticalle, Abra Málaga 13°08'02"S, 072°19'41"W, 3690 m, 30 May 2006, Toivonen 88 (CUZ!); 89 (CUZ!); 90 (CUZ!); 91 (CUZ!); Cerca Canchayoc, 3600 m, 29 June 1967, Vargas 19872 (CUZ!); Canchayoc, 3650–4000 m, 10 January 1968, Vargas 20086 (CUZ!); Canchayoc, 3700 m, 23 April 1980, Vargas 23311 (CUZ!); Yanamanche Quellomayo, 3600–4000 m, 25 July 1944, Vargas 4457 (CUZ!). Paucartambo, Challabamba, Pumataki, 13°09'16"S, 071°38'33"W, 3671 m, 10 December 2014, Boza 3024 (USM!, Z!); Challabamba, between Acjanaco and Tres Cruces, 13°10'07"S, 071°37'58"W, 3450 m, 10 December 2014, Boza 3025 (USM!, Z!); Trocha Ericsson, Acjanaco, Parque Nacional Manu, 3250–3350 m, 01 September 1990, Cano 4041 (USM!); Qollatambo, Parque Nacional Manu, 3700–3800 m, 10 September 1990, Cano 4319 (USM!); Tres Cruces, Parque Nacional Manu, 3600–3700 m, 06 March 1991, Cano 4588 (USM!); Cerro Chapuyoc, Challabamba, ParqueNacional Manu, 3350–3450 m, 15 March 1991, Cano 4689 (USM!); Valle del Pilcopata, near Accanaco Pass, turnoff to Tres Cruces,13°13'S, 071°35'W, 3500 m, 15 December 1983, Foster 7548 (MO!, USM!); Acjanaco, Parque Nacional Manu, Trocha Ericsson, 3000–3200 m, 22 July 1991, Huapaya 221 (USM!); Region of Acanacu and the Cordillera or Tres Cruces, 3290–3500 m, 07 December 1978, Luteyn 6386 (AAU!, MO!, USM!); Pillahuata, alrededores, Tres cruces, 130 km de Cusco en el camino hacia Pilcopta, 13°05'S, 071°30'W, 2000 m, 04 April 1987, Núñez 7749 (CUZ!, MO!, USM!); Km 130 hacia Kosñipata; incluye Acjanacu, Pillahuata, parte alta del Parque Nacional del Manu y ceja de selva hacia Kosñipata, 13°05'S, 071°30'W, 2600 m, 30 October 1987, Núñez 8482 (CUZ!, MO!); Tres Cruces, Parque Nacional Manu, 3500–3700 m, 01 April 1989, Tovar 10081 (USM!); Abra de Acjanaco-Tres Cruces de Oro, carretera Acjanaco-Pillahuata, 13°07'S, 071°40'W, 3700 m, 13 November 1986, Tupayachi 44; Tupayachi 45 (CUZ!, MO!); Entre Paucartambo y Acjanacu, Abra de Acjanacu, 3500 m, 25 January 1960, Vargas 13130 (CUZ!); Hda. Pillco, Valle de Paucartambi, 2800 m, 12 April 1967, Vargas 19242 (CUZ!); Abra de Acjanacu, 3500 m, 20 June 1986, Vargas 24009 (CUZ!); Quebrada de Acjanacu, 3500 m, 11 December 1942, Vargas 3004 (CUZ!, MO!); Chacapampa, 1800–2000 m, 01 December 1950, Vargas 9909 (CUZ!, MO!). Quispicanchis, Marcapata; 176 km from Cusco on road to Maldonado, Marcapata remmant forest to Cocha, 13°25'S, 070°54'W, 3150 m, 08 March 1991, Núñez 13151 (CUZ!, MO!); entre Abra Walla Walla y Marcapata a 210 km de Cusco, 13°25'S, 070°54'W, 2800–4600 m, 21–25 April 1988, Núñez 9032 (CUZ!, IBE, MO!); Huaillai-Marcapata, junto al río Araza, 2900 m, 11 December 1943, Vargas 3765 (CUZ!); Marcapata, 15–16 February 1929, Weberbauer 7803 (A!, MO!). Urubamba, Pakaymayu, 13°14'11"S, 072°29'38"W, 3861 m, 01 June 2002, Arce s.n (USM!); entre San Luis y Abra Malaga, 13°06'S, 072°22'W, 3500 m, 16 October 2002, Lehnert 444 (GOET!); Machu Picchu’, in Urcoscancha, a pampa above the village of Palcay, 13°09'30"S, 072°31'53"W, 3645 m, 05 July 1982, Peyton 792 (MO!); Lado Oriental de Cumbre Málaga, 01 October 1984, Rivas s.n (USM!); Machupicchu, campamento (km 90), 13°11'17"S, 072°26'10"W, 3070 m, 02 August 2006, Toivonen 1 (CUZ!); Dist. Machupicchu, campamento (km 90), 13°11'17"S, 072°26'10"W, 3070 m, 02 August 2006, Toivonen 2 (CUZ!); Dist. Machupicchu, Pakaymayu, 13°14'9"S, 072°29'36"W, 3760 m, 24 August 2006, Toivonen 24, 25; 26; 27; 30 (CUZ!); Dist. Machupicchu. Pakaymayu, 13°14'9"S, 072°29'36"W, 3760 m, 13 September 2006, Toivonen 3760 (CUZ!). Huánuco: Pachitea, Dist. de Umari, Comunidad Campesina de San Marcos, 3400 m, 04 March 2010, Beltrán 6740 (USM!); 6760 (USM!); 01 July 1903, Weberbauer 3354 (B, MO!). Junín: Satipo, Cordillera Vilcabamba, Río Ene slope, near summit of divide, 11°39'36"S, 073°40'02"W, 3320 m, 14 June 1997, Boyle 4398 (USM!). San Martín: Mariscal Caceres, Primer derrumbe y laguna del pato y asociadas del P. N. del Río Abiseo, 3250–3450 m, 24 June 1996, Cano 7265 (USM!); Dist. de Huicungo, Parque Nacional Río Abiseo, Callejón Rojas, 3600–3700 m, 06 July 2011, Castillo 1026 (USM!); 959 (USM!); Dist. de Huicungo, zona de Alpamachay, 3200–3300 m, 14 June 2001, León 5224 (USM!); Río Abiseo National Park; forest on edge of Laguna de Chochos, NW corner of park, 07°00'S, 077°00'W, 3300 m, 19 May 1986, Young 3175 (F!, MO!, USM!); Río Abiseo National Park, jucture of Quebrada Misquichilca and Quebrada Quimar, 4 km SE of Condormarca, 07°00'S, 077°00'W, 3500 m, 05 June 1986, Young 3552 (F!, MO!, USM!); forest on the edge of Laguna de Chochos, Chochos, NW corner of Río Abiseo National Park, 07°S, 077°W, 3300 m, 17 July 1987, Young 4863 (MO!, USM!).