Bolivia. Cochabamba: 77 km after Chapare on the road to Todos Santos, 4200 m, 4 Jan 1968, Vuilleumier 465 (holotype: US!; isotypes: MO!, NY!, P!, TEX!,US!, VEN!).

Shrubs or trees 2–7(9) m tall. Leaves strongly congested at the branch tips, imparipinnate with 2 pairs of leaflets, obtrullate in outline, (1.3–)1.7–2.6 × 1.2–2.0 cm; rachises densely sericeous, points of leaflet attachment with a tuft of long; stipular sheaths apically truncate or with spurs, densely lanate on the outer surfaces; leaflets elliptic in outline, second pair from the terminal leaflet the largest, one of this pair 0.8–1.3 × 0.2–0.7 cm; margin entire, apically emarginate or tridentate due to a projection of the mid-vein, basally unequally cordate; upper leaflet surfaces sparsely to densely sericeous; lower leaflet surfaces densely sericeous with whitish hairs 0.6–0.9 mm long. Inflorescences upright, 1.2–1.6(–3.5) cm long, bearing 3 flowers; floral bracts 4.0–7.3 mm long, narrowly triangular, densely sericeous on the outer surface; rachises densely sericeous. Flowers 4.9–5.9 mm diam.; sepals 3–4, ovate, green, densely sericeous outside; stamens 5–9, anthers orbicular, with a dense tuft of straight white hairs on the upper half; styles fimbriate, 3.0–4.9 mm long. Fruits turbinate often slightly twisted, with variable numbers and placement of short spines, densely sericeous; 2.3–5.7 × 1.9–3.9 mm including spines. Diploid.

Polylepispepei has been found in northern to central Bolivia and southern Puno (Peru) where it has been collected at one locality in San Antonio de Putina Province close to the border with Bolivia (Fig. 24). It grows at 3550–4800 m elevation, where it typically forms the uppermost forests, often in isolated patches high above the closed treeline, often on rocky slopes (Sylvester et al. 2017). Forest remnants in sites that are topographically inaccessible to grazing animals and man-made fires support a unique flora with many previously undescribed species (Sylvester et al. 2016) that presumably represents remnants of the natural potential vegetation (Sylvester et al. 2014a). Such inaccessible forest remnants are also characterized by a high proportion (on average 30%) of dead, standing trees, which support a diverse flora of epiphytic bryophytes and lichens (Sylvester et al. 2017). In accessible forests, such dead trees are harvested by the local inhabitants as firewood (Toivonen et al. 2018). The world’s highest vascular epiphytes (Melpomene spp., Polypodiaceae) have been found at elevations of up to 4550 m in forest of P.pepei (Sylvester et al. 2014b). These forests also support the hemiparasite Tristerixlongebracteatus (Desr.) Barlow & Wiens (Loranthaceae) at over 4600 m elevation (Sylvester et al. 2014b). Stands of P.pepei are often very dense, with numerous trunks of relatively small diameters of around 10 cm (Toivonen et al. 2018). Radial tree growth of the species is enhanced by rains in the dry season and varies depending on local conditions including slope and substrate (Jomelli et al. 2012). Vegetative reproduction increases with elevation, to the degree that the uppermost stands have no reproduction by seeds at all (Hertel and Wesche 2008; Toivonen et al. 2018).

Polylepispepei is known from 12 locations with an EOO of 35,111 km² and an estimated AOO of 68 km². Polylepispepei was categorized as VU (A1c) in the World List of Threatened Trees (Oldfield et al. 1998). Later, it was classified as EN (B1b(i,iii)) in the Red List of Threatened Flora of Bolivia (Arrázola and Coronado 2012). It is protected within Madidi and Carrasco National Parks of Bolivia. A stand above Unduavi has been focus of conservation attention due to the presence of the critically endangered bird species Anairetesalpinus (Navarro et al. 2010). Stands of P.pepei are severely threatened by livestock activities that involve annual burns of the grasslands that often extend into the forests. This species survives low to moderate levels of direct use by local extraction of firewood (Navarro et al. 2010). We assess P.pepei as Endangered (A2a, B1a+B2a, C1, D1).

Polylepispepei is very similar to P.rodolfovasquezii. It differs by having two pairs of lateral leaflets (versus one pair in P.rodolfovasquezii) and longer inflorescences (1.2–1.6(–3.5) cm) bearing three flowers, whereas P.rodolfovasquezii has shorter inflorescences (0.9–1.1 cm) bearing just one flower. Additionally, P.pepei may be confused with P.subsericans and P.flavipila because they all share short leaflets and inflorescences. Polylepispepei differs from these by having two pairs of lateral leaflets and sericeous hairs, whereas the other two species have one pair of lateral leaflets and strigose hairs in P.subsericans and pilose hairs in P.flavipila.

Bolivia. Cochabamba: Chapare, Km 74 Camino antiguo a los yungas del Chapare entrando por Aguirre, 3760 m, 24 April 1999, Mercado 2207 (MO!); 77 km. after Cochabamba on the road to Todos Santos, 4200 m, 04 January 1967, Vuilleumier 465 (MO!, NY, US!). Tiraque, El Ronco, ceja de monte yungena, 17°00'05"S, 065°39'20"W, 3930 m, 11 May 2005, Alcázar-Johansen 403 (BOLV); El Ronco, Ceja de monte yunguena, 17°00'05"S, 065°39'20"W, 3710 m, 11 May 2005, Johansen 403 (MO!). La Paz: Bautista Saavedra, Area Natural de Manejo Integrado Apolobamba, Hilo Hilo, a una hora y media de Pallalani en direccion a Laji Sorapata, sobre el camino, 14°52'40"S, 068°55'34"W, 4300 m, 06 April 2009, Loza 589 (LPB, MA, MO!, USZ); 590 (LPB, MO!, QCA!, USZ). Franz Tamayo, Parque Nacional Madidi, Queara, sector Quecara, Llantai Cunca, 14°39'01"S, 069°05'01"W, 21 April 2008, Fuentes 12687 (BOLV, CTES, HSB, LPB, MA, MO!, QCA!, USZ); Area Natural de Manejo Integrado Apolobamba, Keara, hacia el NW, 14°41'03"S, 069°05'35"W, 4151 m, 17 June 2005, Fuentes 8282 (LPB, MA, MO!, QCA!); Area Natural de Manejo Integrado Apolobamba, Waca Cocha, 4.7 km al SE de Keara, 14°43'47"S, 069°04'17"W, 18 June 2005, Fuentes 8341 (LPB, MO!, QCA!); Area Natural de Manejo Integrado Apolobamba, Hilo Hilo, frente a Pallalani, 14°52'49"S, 068°57'09"W, 4286 m, 05 April 2009, Loza 587 (LPB, MO!, QCA!, USZ); 588 (BOLV, LPB, MO!, QCA!, USZ); Parque Nacional Madidi, Queara nuevo, Chuñuña, queñual al N del pueblo, 14°41'04"S, 069°05'36"W, 4100 m, 09 April 2008, Paco 1 (BOLV, DAV, HSB, LPB, MA, MO!, USZ); Area Natural de Manejo Integrado Apolobamba, Queara nuevo Toilcacocha, 14°41'12"S, 069°05'17"W, 3930 m, 11 April 2008, Paco 80 (LPB, MA, MO!, QCA!, US!); Apolobamba, Puina, cerca de Queñuapata, 14°36'26"S, 069°05'52"W, 4365 m, 10 April 2008, Quisbert 801 (BOLV, LPB, MA, MO!, NY, USZ); 810 (LPB, MA, MO!, USZ); Apolobamba, entre la comunidad de Puina y cerro k’akepununa, 14°36'24"S, 069°05'47"W, 4458 m, 11 April 2008, Quisbert 821 (LPB, MA, MO!, USZ); 825 (BOLV, LPB, MA, MO!, QCA!, USZ); Apolobamba, Palomani, 14°34'58"S, 069°07'38"W, 4286 m, 12 April 2008, Quisbert 844 (BOLV, HSB, LPB, MA, MO!, QCA!, USZ); 848 (BOLV, LPB, MA, MO!, USZ). Inquisivi, 15 Km N Villa Victoria, ca. 15 km SE Quime, 17°06'S, 067°14'W, 4050 m, 05 December 1991, Kessler 3385 (AAU!, GOET!, MO!); 3386 (AAU!, GOET!, MO!). Murillo, entre Pongo y Unduavi, MIna 50, subiendo hacia la Mina SAn Luis, 3960 m, 28 October 1994, Beck 21532 (LPB); Pongo bajanado a los Yungas, del pueblo Pongo subiendo a los restos del bosque de Polylepispepei, 16°19'32"S, 067°57'26"W, 3950 m, 10 January 2007, Beck 29771 (LPB); Valle del Zongo entrando arriba de Botijalca (Tiquimani) haia el Este, Umapalca media hora y entrando en Valle Latera, 16°12'S, 068°03'W, 4000 m, 31 January 2004, Beck 30014 (LPB); 14.8 km N of the pass at the head of The Zongo Valley, 16°13'S, 068°07'W, 3850–4050 m, 11 April 1987, Brandbyge 584 (AAU!); 854 (MO!); Valle del Río Zongo. 14.8 km al norte de la cumbre, 16°12'S, 068°07'W, 3900–4000 m, 20 February 1987, Solomon 16172 (LPB, MO!); 17.0 km al este de La Cumbre (vieja estación de ferrocarril) por el camino a Unduavi (4.2 km al oeste de Unduavi), 16°19'S, 067°55'W, 3350 m, 11 April 1988, Solomon 18267 (LPB, MO!). Nor Yungas, arriba de Unduavi subiendo aproximadamente 45 min hacia los bosques de Polylepispepei, 16°18'S, 067°56'W, 4120 m, 13 September 2016, Escobari 78 (LPB). Sud Yungas, debajo de Unduavi, subiendo el valle de Cerromarca, 3450 m, 28 August 1988, Beck 14680 (LPB).

Peru. Puno: San Antonio de Putina, Tocko-Tocko, 14°43'56"S, 69°36'21"W, 4560 m, 10–12 June 1969, Vargas 21596 (CUZ!).