Polylepis nana (M.Kessler) T.Boza & M.Kessler, comb. et, 2022

Boza Espinoza, Tatiana Erika & Kessler, Michael, 2022, A monograph of the genus Polylepis (Rosaceae), PhytoKeys 203, pp. 1-274 : 1

43. Polylepis nana (M.Kessler) T.Boza & M.Kessler, comb. et stat. nov.

Figs 110 , 111

Polylepis tomentella subsp. nana M. Kessler (1995b: 166). Type. Based on Polylepis nana (M.Kessler) T.Boza & M.Kessler.

Type.

Bolivia. Dept. Cochabamba, Prov. Arani, 2 km W turn-off to Vacas from Arani-Mizque road, l 7°33'S, 65°42'W, 3200 m, 18 Aug1991, Kessler 3409 (holotype: LPB!; isotypes: AUU!, GOET!) .

Description.

Shrub to 2 m tall. Leaves slightly congested at the branch tips, imparipinnate with one pair of leaflets, trullate in outline, 1.7-2.4 × 1.2-1.9 cm; rachises densely villous, points of leaflet attachment with a tuft of long hairs; stipular sheaths apically truncate or slightly spurred, densely villous on the outer surfaces; leaflets obovate in outline, second pair from the terminal leaflet the largest, one of this pair 1.0-1.2 × 0.3-0.5 cm; margin serrate with 5-8 teeth, apically acute, basally unequally attenuate; upper leaflet surfaces often with dark sheen, glabrous to sparsely villous; lower leaflet surfaces with a dense layer of very short, white or yellowish pannose hairs. Inflorescences pendant, 0.9-1.2 cm long, bearing 2-4 flowers; floral bracts 2.4-3.1 mm long, narrowly triangular, densely villous on the outer surface; rachises villous. Flowers 5.4-6.8 mm diam.; sepals 3, ovate, green, sparsely villous outside; stamens 12-15, anthers orbicular, with a dense tuft of straight white hairs on the upper half; styles fimbriate, 3.0-3.3 mm long. Fruits turbinate, with 3-4 irregular flattened ridges with a series of spines, densely villous; 5.0-7.7 × 3.0-3.3 mm including spines. Tetraploid.

Distribution, habitat and ecology.

Polylepis nana is restricted to Cochabamba (Bolivia) where it has been collected at just one locality in Arani Province (Fig. 116 ). It grows at 3200-3450 m elevation.

Conservation status.

The EOO for Polylepis nana is estimated as 8 km2, the AOO is assessed at 8 km2 and it is known from only one location. No conservation action has been taken to date. Polylepis nana was categorized as CR (B1+2c, C2b) in the World List of Threatened Trees ( Oldfield et al. 1998). However, it was classified as EN (B1ab(i,ii,iii)) in the Red List of Threatened Flora of Bolivia ( Arrázola et al. 2012). The only known locality consists of extensive, but heavily degraded stands in the Arani-Vacas area where they are strongly threatened by overgrazing, logging and burning of grasslands. We assess P. nana as Critically Endangered (A1+A2a, B1a, C1+ C2a, D2a).

Notes.

Polylepis nana can be distinguished from the most similar species P. tomentella by its shrubby growth form, smaller leaflets (1.0-1.2 × 0.3-0.5 cm vs. 1.3-2.0 × 0.5-0.7 cm) with acute apex (vs. round to slightly emarginated), shorter inflorescences (0.9-1.2 cm vs. 2.8-5.3 cm) with fewer flowers (2-4 vs. 4-5), fewer stamens per flower (12-15 vs. 19-25) and longer styles (3.0-3.3 mm vs. 2.4-2.5 mm).

Specimens examined.

Bolivia. Cochabamba: Arani, between Arani and Cañadas on the road to Vacas, 17°34'S, 065°40'W, 3100 m, 20 April 1987, Brandbyge 708 (AAU!); Kewiñal, 3300 m, 24 March 1991, Hensen 1949 (LPB); 2012 (LPB); 2 km after turnoff to Vacas on Mizque-Arani road, 17°33'S, 065°42'W, 3100 m, 18 August 1991, Kessler 2998 (GOET!, LPB); 2 km W turnoff to Vacas from Arani-Mizque road, 17°33'S, 065°42'W, 3200 m, 18 August 1991, Kessler 3403; 3404 (GOET!, LPB); 3405 (GOET!); 3406; 3407 (GOET!, LPB); 3408 (GOET!, LPB, USM!); 3409 (AAU!, GOET!); 3495; 3501; 3514; 3518; 3519; 3521; 3641 (GOET!); 3642 (GOET!); camino a Vacas, 3170 m, 11 January 1990, Saravia 17 (LPB) .

Figures

Figure 110. Polylepis nana (M. Kessler) T. Boza & M. Kessler A branching pattern B branching pattern. Photographs by M. Kessler.

Figure 111. Polylepis nana (M. Kessler) T. Boza & M. Kessler A flowering branch B stipular sheaths C fruit D lower leaf surface E upper leaf surface (A Kessler 3512 B Kessler 3495 C Kessler 3513 D Kessler 3642 E Kessler 3520). Scale bars: 8 cm (A); 6 mm (C); 1 cm (D, E). Photographs by T. E. Boza E.

Figure 116. Geographical distribution of the species of subsection Polylepis Incanaee Incanaee.