Ecuador. Chimborazo: Lagunas de Atillo, 02°08'S, 78°34'W, 3465 m, 17 Dec 2019, K. Romoleroux, T.E. Boza E. & E. Bastidas 6199 (holotype: QCA!; isotype: Z!).

Trees 4–12 m tall. Leaves strongly congested at the branch tips, imparipinnate with 3–4 pairs of the lateral leaflets, obtrullate in outline, 4.5–6.3 × 3.4–4.3 cm; rachises densely sericeous, points of leaflet attachment with a tuft of long, straight whitish hairs; stipular sheaths apically acute with spurs, densely sericeous in the upper surface; leaflets elliptic in outline, second pair from the terminal leaflet the largest, one of this pair 1.8–2.8 × 0.6–0.9 cm; margin entire, apically emarginate, basally unequally cordate; upper leaflet surfaces glabrous; lower leaflet surfaces densely sericeous with whitish hairs 0.2–0.4 mm. long. Inflorescences pendant, 13.0–17.9(–20.4) cm long, bearing 23–29 flowers; floral bracts 9.3–11.1 mm long, narrowly triangular, densely sericeous on the outer surface; rachises glabrous. Flowers 7.4–8.4 mm diam.; sepals 4, ovate, green, densely sericeous outside; stamens 9–15, anthers orbicular, with a dense tuft of straight white hairs on the upper half; styles fimbriate, 1.9–2.9 mm long. Fruits turbinate, with variable numbers and placement of flattened spines, densely sericeous; 3.3–5.1 × 3.1–7.4 mm including spines. Diploid.

Polylepishumboldtii is restricted to Chimborazo Province in Ecuador (Fig. 41). It occurs in small populations in mixed Andean Forest at 3800–4000 m elevation.

The AOO is estimated as 4 km² and it has been collected at only two locations in Ecuador. Although it is protected within Sangay National Park, burning of the páramo grassland matrix likely affects the remaining Polylepis forest patches. Therefore, we assess P.humboldtii as Critically Endangered (B2a, C2).

Polylepishumboldtii seems morphologically closest to P.sericea with which it shares similar leaflet shape, margin, apex and upper and lower leaflet surfaces hairs type and density. The most obvious differences between these species are leaflet hair length, with P.humboldtii having shorter hairs than P.sericea (0.2–0.4 mm versus 0.7–1.0 mm) and longer inflorescences (13.0–20.4 cm) with more flowers (23–29) than P.sericea (3.3–4.5 cm, 9–15 flowers). Additionally, P.humboldtii occurs in central Ecuadorean Andes, whereas P.sericea is distributed from western Venezuela to central Colombia.

Ecuador. Chimborazo: Alausí, Achupallas, alrededores, 2°17'S, 78°39'W, 3300 m, 11 July 2013, Caranqui 2565 (QCA!); Lagunas de Atillo, 2°8'S, 78°34'W, 3465 m, 13 April 2009, Carate et al. 184; 185; 188 (QCA!).