Guyana • Potaro-Siparuni, Mt Ayanganna, East slope, summit plateau; 5°23′18"N, 59°58′54"W; 1955m; fl.; 20 Mar 2014; A. Radosavljevic et al. 247 (holotype: NY 04078880, isotype US 03457967) (Figs 1–4).

Shrub or small tree up to 1.5 m tall. Branchlets often with remnants of inflorescences below the congested leaves. Leaves alternate, sessile or with a petiole c. 1 mm long, leaf blade (1–)1.5–4 × (0.5–)1–1.8 cm, coriaceous, obtrullate, rarely rhombic or narrowly rhombic, base cuneate, apex slightly rounded to acuminate, margins crenulate, abaxial surface glabrous, with sparse black glands when dried, secondary veins scarcely visible, adaxial surface glabrous, rarely with black glands; venation pinnate with no naked basal veins, one basal vein, and no agrophic veins (Fig. 4), the major secondaries semicraspedodromous with irregular spacing, the secondary angle slightly increasing proximally, and with decurrent attachment to the midvein, the minor secondaries and interior secondaries absent, the intersecondaries parallel, spanning less than 50% of the length of the subjacent secondaries, the intercostal tertiary veins irregularly reticulate, the epimedial tertiaries ramified with the admedial course parallel to the subjacent secondary and the exmedial course parallel to the intercostal tertiary, the exterior tertiaries terminating at the margin, the quaternary vein fabric irregularly reticulate, the quinternary vein fabric freely ramifying, areolation well developed, freely ending veinlets with two or more dendritic branches. Inflorescence axillary or occasionally terminal, once-paniculate, 2 cm long, with each branch bearing 3–4 flowers; bracts 2–3 × ca. 0.5 mm, oblanceolate to narrowly oblong, base truncate, rarely cuneate, apex rounded, margin ciliate; pedicels 2–3 mm long. Flowers 1.2–1.5 cm long, sepals 5, 2–4 × 1–2 mm, heteromorphic in size, oblong or ovate, apex rounded to acuminate, glabrous, margin ciliate, with sessile glands on the external surface; petals 5–6, 7–8 × 5–6 mm, broadly obtrullate, apex obcordate with asymmetric lobes, base cuneate, white with red margins; stamens 70–80, yellow, filaments 3 mm long, glabrous, anthers ca. 0.6 mm long; gynoecium ca. 5 × 2.5 mm, locules 3, carpels 3, green or yellow, stigma 3-branched in the upper fifth, the lobes reflexed. Capsules 7–8 × 3–3.5 mm, widely ovate to ovate. Seeds 1.5–2 mm long, linear.

Guyana • Potaro-Siparuni, Mt. Ayanganna, east face, edge of summit plateau; 5°23′18′′N, 59°58′56′′W; 2000 m elev.; fl., fr.; 24 June 2001; D. Clarke et al. 9524 (NY, US).

Bonnetiaayangannensis is morphologically most similar to B.paniculata Spruce ex Benth., but it differs from that species by the leaf blades (1–)1.5–4 cm long (vs. 6–18 cm in B.paniculata), the leaves with glandular punctuations on the abaxial surface (vs. glands absent), the bracts 2–3 mm long (vs. 6–7 mm), the sepals ciliate and glandular (vs. cilia and glands lacking) and 2–4 × 1–2 mm (vs. 10 mm × 6–7 mm). Bonnetiatepuiensis Kobuski & Steyerm. and B.rubicunda (Sastre) A.L. Weitzman & P.F. Stevens also occurs on the summit of Mount Ayanganna, however the new species can be differentiated by the leaves cuneate at base (vs. rounded in B.tepuiensis), the flowers pedicellate (vs. sessile), arranged in inflorescences (vs. solitary flowers) and by having leaf with venation pinnate and flowers with sepals and petals less than 8 mm long (vs. parallel leaf venation and sepals and petals more than 18 mm long in B.rubicunda). For better identification of the Bonnetia species of Guyana, see the identification key below.

The voucher Clarke et al. 9535 (NY 04067354) is a mixed specimen, consisting of three branches of B.tepuiensis, and a small branch to the right of B.ayangannensis.

The epithet refers to the tepui Mount Ayanganna, where the new species was discovered.

Bonnetiaayangannensis appears to be endemic to the summit area of Mount Ayanganna tepui, Potaro-Siparuni, in western Guyana. The species is known from only two collections gathered in close proximity from a single population on the eastern summit slope of Mount Ayanganna. The species occurs in scrub forest on sandstone, together with B.tepuiensis, Clusia spp. (Clusiaceae), and Brocchinia spp. (Bomeliaceae), among others, at elevations between 1900 and 2000 m.

We recommend that Bonnetiaayangannensis be assigned to the Critically Endangered category based on criterion B2ab(iv). The species is known from basically a single location (the two collection localities being separated by only c. 0.06 km), yielding an area of occupancy of 4 km², assuming the default settings in GeoCAT (Bachman et al. 2011; Bachman and Moat 2012). However, considering that the area above 1900 m elevation on Mount Ayanganna, where taller forest gives way to scrub forest, is only about 0.7 km², we suspect that the actual AOO is substantially less than 4 km². Moreover, it is likely that the population will undergo anthropogenic climate change-driven reduction, paralleling reduction in the extent of the summit scrub vegetation on Mount Ayanganna, the summit peak of which is only 2041 m elevation. This projection is based on modeling (Nogué et al. 2009) that suggests upward migration and potential habitat loss for many species with restricted tepui distributions. This, in turn, subjects these localities to threats according to the conditions of subcriterion b(iv). Other species occurring in the eastern district of Pantepui, which are endemic to the summit of one or a few tepuis, are also threatened by rising temperatures, as is the case with B.fasciculata P.F.Stevens & A.L.Weitzman (Nogué et al. 2009) or are already listed on the IUCN Red List, such as B.rubicunda (Vulnerable) and B.ptariensis Steyerm. (Critically Endangered) (World Conservation Monitoring Centre 1998a, World Conservation Monitoring Centre 1998b).

The leaves have a crenulate margin, sometimes bearing deciduous spinular projections (Fig. 2A). The abaxial leaf surface is rugose (i.e., not smooth and presenting different levels) and bears many sessile glands and stomata (Fig. 2B). At higher magnification, the surface takes on a warty-crustose appearance with granular projections (Fig. 2C). The margins of the bracts have short stalked glands with thin-walled elongate heads (Fig. 2D, E). The sepals have sessile glands on the external surface (Fig. 2F) and short stalked glands on the margins (Fig. 2F, G). The seeds bear longitudinal striations (Fig. 2H).