This species differs from P.triacontandra Bitter by its smaller leaflets with different type and length of hairs and shorter inflorescences with lower number of flowers.

Peru. Cusco: Acomayo. Rondocan, bosque de Llamacocha, 13°50'34"S, 072°02'31"W, 3933 m, 12 Jul 2015, T.E. Boza E. & E. Urquiaga 3038 (holotype: USM!; isotype: Z!).

Trees 3–8 m tall. Leaves slightly congested at the branch tips, imparipinnate with 1(–2) pair of leaflets, obtrullate in outline, (2.7–)3.5–4.5 × 2.6–3.3 cm; rachises densely villous, points of leaflet attachment with a tuft of long hairs; stipular sheaths apically truncate, densely villous on the outer surfaces; leaflets narrowly obovate in outline, second pair from the terminal leaflet the largest, one of this pair 1.6–2.3 × 0.5–0.9 cm; margin crenate with 6–9 teeth, apically round or emarginate, basally acute; upper leaflet surfaces sparsely villous; lower leaflet surfaces densely villous with whitish hairs 0.9–1.1 mm long mixed with pannose hairs, second pair of leaflets, if present, very small. Inflorescences pendant, 2.0–4.0 cm long, bearing 5–7 flowers; floral bracts 3.9–4.2 mm long, narrowly triangular, densely villous on the outer surface; rachises villous. Flowers 10.2–10.7 mm diam.; sepals 4, ovate, green, densely villous outside; stamens 19–25, anthers orbicular, with a dense tuft of straight white hairs on the upper half; styles fimbriate, 2.3–4.0 mm long. Fruits turbinate, with 2–3 irregular flattened ridges with a series of spines, densely villous; 4.2–5.7 × 3.2–4.4 mm including spines. Tetraploid.

Polylepisacomayensis occurs in southern Cusco (Peru) in relatively cold and dry Andes at 3800–4160 m elevation (Fig. 92). It grows in mixed forests with Escalloniaresinosa.

This species is named after Acomayo, the Province to which its distribution appears to be restricted.

The EOO for Polylepisacomayensis is estimated as 110 km², the AOO is assessed at 12 km² and it is known only from three locations. The species is unprotected. Logging, grazing and agriculture are the most important activities affecting these forests. We assess P.acomayensis as Endangered (A2a, B1a+B2a, C2a).

Polylepisacomayensis resembles P.triacontandra in having 1(–2) lateral leaflets pairs as well as similar leaflet margin and density of hairs. However, it has narrowly obovate leaflets 1.6–2.3 × 0.5–0.9 cm long with villous hairs 0.9–1.1 mm long and inflorescences 2.0–4.0 cm long with 5–7 flowers, whereas P.triacontandra has narrowly elliptic leaflets (2.0–)2.6–3.3 × 0.7–1.1 cm long with tomentose hairs 0.4–0.8 mm long and inflorescences 4.9–9.5 cm long with 11–13 flowers. Polylepisacomayensis is also morphologically similar to P.sacra with which it shares similar leaflet size, margin and hair density. The most obvious differences between P.acomayensis and this species are the number of lateral leaflet pairs, with P.acomayensis having 1(–2) pairs, whereas P.sacra has 2–3 pairs. Furthermore, P.acomayensis has villous hairs 0.9–1.1 mm long and inflorescences 2.0–4.0 cm long whereas P.sacra has lanate hairs 1.3–1.5 mm long and inflorescences 5.0–8.8 cm long.

Peru. Cusco: Acomayo, Rondocan, Llamacocha, 13°50'53.6"S, 71°45'32.7"W, 3933 m, 12 July 2015, Boza & Urquiaga 3038; 3122; 3123; 3124; 3125; 3126; 3127; 3128; 3129; 3130; 3131; 3132 (USM!, Z!). Paruro, Accha, Kangal, 13°59'41.2"S, 71°48'42.3"W, 4194 m, 12 July 2015, Boza & Urquiaga 3039; 3133; 3134; 3135; 3136; 3137; 3138; 3139; 3140; 3141; 3142; 3143 (USM!, Z!).