Handroanthus abayoy Villarroel & G. A. Parada. A. Leaves. B. Flowers 2022, sp. nov.

Handroanthus abayoy Villarroel & G.A.Parada, sp. nov. (Figure 1; Figure 2)

Type: — BOLIVIA. Santa Cruz, Provincia Germán Busch: afloramiento rocoso, zona del Calvario del Carmen Rivero Torrez, 18.809112°S, 58.619919°W, 211 m, 11 July 2021, fl, G. A. Parada 5609 (holotype USZ!, isotypes K!, LPB!, MO!).

Handroanthus abayoy is similar to H. selachidentatus but differs in the absence of lepidote scales, stellate trichomes and resinous exudate on the calyx and branches; and in the basally asymmetrical leaflets, lateral petiolules 1–2.5(–3) cm long, and in the blades with margins entire, repand, crenulate or slightly serrate, mainly at the apex, and also in the inflorescences and flowers with dendroid trichomes, and in the pulverulent calyx.

Tree, 1–3 m tall when growing on rocky outcrops, 2–8 m tall when growing on sandy soils in the lowland plains, and up to 15 m at the foot of mountains and on plateaus; stems> 5 cm dbh (diameter at breast height), bark strongly fissured, woody rhytidome, yellowish-coloured; apical branches cylindrical or slightly subtetragonal, glabrous and with scattered lenticels; leaf buds and the extreme apices pulverulent, with whitish dendroid trichomes. Leaves 1–3-foliolate, opposite, petiole 3.5–5(–6) cm long, 2–3 mm diametre, canaliculate; lateral leaflets with petiolules 1–2.5(–3) cm long, canaliculate, blades 4–7.5(–8) × (2.3–)2.5–4 (–4.5) cm, elliptical, ovate or orbicular, base asymmetric to slightly asymmetric, obtuse or rounded, sometimes truncate, apex acuminate or cuspidate; terminal leaflets with petiolules (1.5–) 2–3.5 cm long, canaliculate, blades 5.5–8(–10) × 3–4.5(–5.5) cm, elliptical, ovate or orbicular, sometimes oblanceolate, coriaceous, glabrous, base asymmetrical, obtuse or rounded, sometimes truncate, apex acuminate or cuspidate; margin strongly cartilaginous, entire, repand, crenulate or slightly serrate (mainly at the apex), discolorous, the upper surface glaucous green or dark green and lustrous, the lower surface light green and cinereous, both surfaces with visible scattered flat and circular nectaries, with visible translucent glands, dispersed, 0–2 per mm 2; midvein slightly sulcate on the upper surface, prominent on the lower surface; secondary veins 6–10-paired, brochidodromous or cladodromous, arched, angle of divergence 30–45°, prominent on both surfaces; tertiary veins reticulate, prominent on both surfaces. Inflorescences paniculate, terminal, with 6–11 flowers per panicle; peduncle pulverulent, trichomes dendroid and whitish; bracts and bracteoles deciduous, 1–1.5 mm long, concave and deltoid, apex acute, pulverulent on both surfaces (whitish trichomes, dendroid), the margin ciliate, trichomes dendroid and whitish. Flowers pedicellate, pedicel articulate, 2–3 mm long; calyx cupular, 4–5.5 mm long, 4–5 mm wide in the middle, 5-lobed, the lobes irregular, c. 1–1.5 mm long, slightly concave, the apex rounded or acute, margin entire, not ciliate, both surfaces dark purple-coloured, the exterior pulverulent with whitish dendroid trichomes, the interior glabrous or glabrescent; corolla tubular-infundibuliform, 4.5–5.5 cm long, floral tube 3–4.5 cm long, exterior white at the base and pink or magenta along the tube, pilose or pubescent (trichomes dendroid and whitish), interior white but with yellow patches in the throat, glabrous or glabrescent (trichomes dendroid and whitish), 5-lobed, the lobes 1.5–2 cm long, 1–1.5 mm wide at the base, pink or magenta on both surfaces, the apex rounded, pilose or pubescent on both sides, margin sinuous and ciliate (trichomes dendroid and whitish); stamens 4, inserted, free part of the dorsal filaments 1–1.3 cm long, free part of the ventral filaments 1.5–1.8 cm long, free part glabrous, adnate part tomentose with glandular trichomes, anthers glabrous, thecae c. 2.5–3 × 1 mm; ovary 2-locular, c. 3.5–4 × 1–1.5 mm, linear-oblong in outline, not ribbed, 2–3 series of ovules per locule, 11–14 ovules per locule; nectary disk annular; style 3–3.5 cm long, glabrous, stigma bifid, lobes c. 1.5 × 1 mm, glabrous. Fruits linear capsules, 15–22 × 0.5–1 cm, cylindrical in cross section, glabrous or glabrescent; valves membranous, smooth; calyx persistent. Seeds bialate, 0.5–0.8 × 2–3.5 cm, the wings hyaline-membranaceous, sharply demarcated from darker seed body.

Paratypes:— BOLIVIA. Santa Cruz, Prov. Chiquitos: 25 km al S de San José, camino a las Salinas, 300 m, 27 August 1997, fl, A. Fuentes & G. Navarro 2047 (LPB!, USZ!); Serranía de Santiago de Chiquitos, senda a Soledad, 18°21.11’S, 59°35.5’W, 622 m, 2 March 2007, st, P. Pozo 370 (LPB!); Santiago de Chiquitos, ca. 2 km de Santiago de Chiquitos en el camino hacia Roboré, 18°20’S, 59°36’W, 500 m, 3 September 2007, fl, J. R. I. Wood 23375 (LPB!, USZ!); subida de Santiago a 3 kilómetros de la plaza en el camino a Roboré, 18.2014°S, 59.36307°W, 612 m, 7 October 2008, fr, J. R. I. Wood & P. Pozo 25078 (K, LPB, USZ!); carretera entre Roboré y Aguas Calientes, 18°23’45.8”S, 59°39’12.9”W, 260 m, 5 September 2020, fl/fr, D. Villarroel 6265 (LPB, USZ!); carretera entre Roboré y San José de Chiquitos, ca. 2 km al NW de Ipiás, 18°01’41”S, 60°11’52.7”W, 415 m, 31 July 2021, fl, D. Villarroel 6274 (USZ!, K, LPB); Prov. Germán Busch: a 700 metros aprox. de la carretera Ruta 4, sobre bosque bajo sobre arenales (abayoy), 18.799008°S, 58.664673°W, 174 m, 20 September 2020, fr, G. A. Parada 5484 (LPB, MO, USZ!).

Distribution, habitat and phenology:— Handroanthus abayoy is an endemic species of the southern part of the Department of Santa Cruz (Bolivia), occurring in the municipalities of Roboré and San José de Chiquitos of Chiquitos Province and the municipality of Carmen Rivero Torrez in Germán Busch Province. It is a deciduous tree, typical of the abayoy vegetation, that is distributed between 150–600 m elevation and bordered to the west and south by the Chaco vegetation, to the east by the Pantanal wetlands, and to the north by the Cerrado and Chiquitano Dry Forest (Ibisch et al. 2003, Navarro 2011, Villarroel et al. 2016). The abayoy vegetation develops on plains with quaternary sediments, where the soils are deep, sandy, acidic and well drained. Biogeographically, the abayoy vegetation has a high floristic affinity with the Cerrado, although it also presents floristic elements typical of the Chaco. Handroanthus abayoy is a frequent and relatively abundant species [9±5 tree/ha, value calculated from Villarroel et al. (2010), Villarroel et al. (2021)]. Due to the glaucous-green colour of its leaves, as well as the color of its flowers, H. abayoy is a conspicuous element of the landscape. Although with lesser frequency, it also inhabits in the cerrado rupestre and the cerradão in the Serranía Chiquitana between 300 and 650 m [the habitats or phytophysiognomies follow the classification of Ribeiro & Walter (2008) and Villarroel et al. (2016)]. Handroanthus abayoy start flowering in the middle of the dry season (July), produces flowers until early September, at the end of the dry season. Fruiting occurs between the end of the dry season and the beginning of the wet season (September and October).

Etymology:—The specific epithet “ abayoy ” refers to the main type of vegetation where the species lives, the abayoy, a word from the Bésiro language that means dwarf forest. This type of vegetation has a series of biotic and abiotic characteristics that differentiate it from the Pantantal, the Chaco and the Chiquitano Dry Forest; being, biophysically more similar to the Cerrado (Ibisch et al. 2003, Navarro 2011, Villarroel et al. 2016).

Conservation status:—All records of Handroanthus abayoy are restricted to the southern region of the department of Santa Cruz, Bolivia (Figure 3). It is known from eight localities, one of these within the Tucabaca Conservation and Natural Heritage Unit (UCPN), another within the Santa Cruz la Vieja UCPN, and two within the Ñembi Guasu Conservation and Ecological Importance Area (Figure 3). The extent of occurrence (EOO) of the species is 9,195.1 km 2, and the area of occupancy (AOO) 40 km 2. Currently, the populations that inhabits the cerrado rupestre and the cerradão in the Serranía Chiquitana have low human pressure (it grows on rocky outcrops, serpentine soils or on shallow soils on the Precambrian Shield). However, the populations that inhabit the abayoy vegetation are threatened by agricultural and livestock expansion and have also been severely affected by forest fires in 2019 (Villarroel et al. 2021).

Therefore, H. abayoy should be categorized as Vulnerable [VU B2 ab (iii)], according to IUCN criterion B2 (AOO <2,000 km 2) (IUCN 2019); sub-criteria a, number of locations ≤10; and the sub-criteria b (iii), continuous decrease in the area of extension and / or quality of habitat (deforestation and forest fires).

Affinities:— Handroanthus abayoy is similar to H. selachidentatus. The latter is currently recognized in the Catalogue of Vascular Plants of Bolivia (Jørgensen et al. 2015 onwards) based on the publication by Fuentes-Claros (1998). However, the specimen cited by Fuentes-Claros (1998) corresponds to H. abayoy. Both species are part of Tabebuia group II in the clades proposed by Grose & Olmstead (2007), because of the cupular 5-lobed calyx and magenta flowers with a yellow throat. However, both species have a series of morphological (vegetative and reproductive) and biogeographic characteristics that distinguish them one from another (Table 1).