Bolivia. La Paz: Murillo, sobre el camino de herradura entre Cohoni y Jalancha, 16.6853°S, 67.8356°W, 3853 m, Mendez & Arcienga 18 (holotype: GOET!; isotype: LPB!).

Trees 3–8 m tall. Leaves slightly congested at the branch tips, imparipinnate with 2–3 pair of leaflets, obtrullate in outline, 3.4–5.2 × 2.4–3.4 cm; rachises densely villous, points of leaflet attachment with a tuft of long hairs; stipular sheaths apically acute with spurs, densely villous on the outer surfaces; leaflets obovate in outline, second pair from the terminal leaflet the largest, one of this pair 1.7–2.4 × 0.6–0.8 cm; margin crenate, apically emarginate, basally cuneate; upper leaflet surfaces glabrous to sparsely villous; lower leaflet surfaces with an evenly distributed dense layer short white pannose hairs, admixed with villous whitish hairs 0.4–0.9 mm long. Inflorescences pendant, 3.7–7.7(–10.0) cm long, bearing 5–11 flowers; floral bracts 4.3–5.0 mm long, narrowly triangular, sparsely to densely villous on the outer surface; rachises densely villous. Flowers 6.5–8.1 mm diam.; sepals 4, ovate, green, densely pannose outside; stamens 17–23, anthers orbicular, with a dense tuft of straight white hairs on the upper half; styles fimbriate, 2.3–2.7 mm long. Fruits turbinate, with 3–4 irregular flattened ridges with a series of spines, densely pilose; 5.4–7.3 × 4.7–5.6 mm including spines. Tetraploid.

Polylepispacensis is distributed in southern La Paz and western Cochabamba Departments (Bolivia) (Fig. 92). It occurs in relatively dry inter-Andean valleys at 3400–4700 m elevation. It co-occurs with P.triacontandra on Cerro Illimani (Kessler and Schmidt-Lebuhn 2006). Some forests of P.pacensis show an influence of humid Yungas forests, as indicated by the presence of Oreopanaxmacrocephalus, Brachyotummicrodon and Phytolaccabogotensis. In drier areas, close to inaccessible streams with steep slopes and, therefore, unsuitable for crops, P.pacensis co-occurs with other native species, such as Escalloniaresinosa, Puya sp., Schinusmicrophylla and Azorellamultifida (Hurtado et al. 2018). In a study in Cohoni (La Paz), natural regeneration was abundant and successful in places protected by topography where human and animal access is difficult, with an average of 1312 seedlings/ha. Polylepispacensis has a mean germination rate of 8%, which decreases with elevation (Mendez 2005; Vega et al. 2018).

The EOO for Polylepispacensis is estimated as 15,486 km², the AOO is assessed at 44 km² and it is known from 44 locations. No conservation actions have been taken to date. It has been categorized as EN (B1ab(i,ii)) (Arrázola and Coronado 2012). Based on the small size of the remaining populations, the extraction of firewood represents a major threat. We assess P.pacensis as Endangered (A2b, B1a+B2a, C1).

Polylepispacensis was considered by Simpson (1979) to belong to the broadly defined P.racemosa. Kessler (1995b) was unable to place the few specimens available at that time under either P.triacontandra (which occurs mainly to the north) and P.lanata (southwards). It was only when new herbarium collections were gathered that the taxonomic distinctness of the species became apparent (Kessler and Schmidt-Lebuhn 2006). Polylepispacensis is similar to P.triacontandra, but has 2–3 pairs of obovate leaflets with villous hairs, whereas the latter has 1(–2) pairs of narrowly elliptic leaflets with tomentose hairs. Polylepispacensis also has fewer flowers per inflorescence (5–11 versus 11–13) and shorter styles (2.3–2.7 mm versus 3.3–3.8 mm). For additional morphological similarities, see under P.lanata.

Bolivia. Cochabamba: Ayopaya, Piusilla, 3300 m, 30 March 1991, Hensen 2134 (GOET!, LPB). La Paz: Bautista Saavedra, 2 kms. arriba de Chajaya, Quebrada de Janajj Wayq’o, 15°11'53"S, 069°00'14"W, 3740 m, 04 August 1985, Beck 11350 (LPB, MO!). Inquisivi, Quime 7 km hacia Caxata, 3420 m, 19 February 1981, Beck 4378 (LPB); 8 km W Quime on road to Caxata, 17°03'00"S, 067°17'00"W, 3350 m, 24 August 1991, Kessler 3029 (AAU!); 3030 (AAU!, GOET!, MO!); 3031 (GOET!, MO!); 3032 (AAU!, GOET!, MO!). Murillo, Palca 28.5 km hacia Cohoni, 3440 m, 14 October 1990, Beck 17832 (GOET!, LPB); aprox. 14 km de población Cohoni (Municipio de Palca) sobre ruta Cohoni–Cayimbaya, 16°41'51"S, 067°00'00"W, 3586 m, 10 November 2014, Bermejo PP 2 S5 (LPB); Subcuenca de Cohoni, camino de herradura Cohoni–Jalancha, 16°39'36"S, 067°49'12"W, 4989 m, 05 January 2003, Mendez 1; 2 (LPB); 3 (GOET!, LPB); 4; 5 (LPB); 6 (GOET!, LPB); 7; 8; 9; 10; 11; 12; 13 (LPB); 14 (GOET!, LPB); 15 (LPB); Sobre el camino carretero a 6 km de Cohoni hacia Palca, 16°40'48"S, 067°51'00"W, 3457 m, 05 January 2003, Mendez 16 (GOET!, LPB); Sobre el camino de herradura entre Cohoni y Jalancha, 16°40'48"S, 067°49'48"W, 3856 m, 13 November 2003, Mendez 17; 18; 19 (GOET!, LPB); Sobre el camino de herradura entre Cohoni y Jalancha, 16°40'12"S, 067°49'48"W, 3879 m, 13 November 2003, Mendez 20 (GOET!, LPB); Subcuenca de Cohini, Cohoni lado de la Jalancha (caida de agua), 16°39'36"S, 067°49'12"W, 4173 m, 13 November 2003, Mendez 21 (GOET!, LPB); ciudad de La Paz, Zona La Portada, Av. Final Kollasuyo interseccion con Av. Naciones Unidas, Plaza La Portada. Jardinera de plaza, 16°29'13"S, 068°09'57"W, 3995 m, 04 March 2016, Vega MUNAY 1 (LPB). Palca, Catagna au pied S I’Illimani, 4511 m, Pentland 47 (GOET!). Quime, about 10 km from Quime on the road to Caxata, 17°00'S, 067°12'W, 3400 m, 25 April 1987, Brandbyge 769 (AAU!).