Ruehssia bahiensis I.C.Oliveira & F.Esp.Santo, 2023

Oliveira, Ilana C., Espírito Santo, Fábio S., Rapini, Alessandro, Dórea, Marcos C. & Oliveira, Reyjane P., 2023, Ruehssia bahiensis: a new species of Apocynaceae endemic to a floristically neglected area within the Semi-arid of Bahia, Brazil, Phytotaxa 629 (2), pp. 147-154 : 148-152

Ruehssia bahiensis I.C.Oliveira & F.Esp.Santo , sp. nov. Type:— BRAZIL. Bahia: Valente, Serra do Pintado ( Povoado de Varginha ), 11º17’56”S, 39º28’43”W, 535 m a.s.l., 01 November 2021, fl., I.C. Oliveira, R.P. Oliveira & M.C. Dórea 13 (holotype HUEFS!) ( Figs. 1 , 2 ).

Diagnosis: Ruehssia bahiensis is similar to R. pickelii , differing by the corolla lobes adaxially pubescent (vs glabrous), gynostegium taller (> 1.5 mm vs ca. 0.8 mm long) and stipitate (vs sessile), corona lobes smaller (<1.7 mm vs> 2.0 mm long), shorter than (vs as high as) the style-head apex, which is conical (vs subglobose) and exserted (vs inserted) from the corolla tube, and pollinia smaller (<0.3 mm × 0.15 mm vs> 0.39 mm × 0.19 mm) ( Tab. 1 ).

Liana, stems glabrous, latex white. Leaves with petiole 0.5–0.9 cm long, glabrous; lamina 7.2–9 × 3.7–4.3 cm, elliptic to ovate, base obtuse to rounded, apex acuminate to cuspidate, margins revolute, adaxially with 2 or 4 colleters at the base of the central vein, membranous, glabrous ( Figs. 1A , 2C ). Inflorescences corymbose, 9–25 flowers; peduncle 1.6–6 mm long, glabrous to sparsely pubescent; bracts narrowly triangular to lanceolate, 2–4 × 0.5–0.9 mm, margins ciliate; pedicels 0.4–0.6 mm long, sparsely pubescent ( Figs. 1B , 2D ). Sepals 4–5 × 1.8–2.1 mm, ovate, margins ciliate, apex acute, abaxially glabrous, occasionally with sparse trichomes, green with vinaceous apex, adaxially with 5 alternisepalous colleters at the base of calyx. Corolla campanulate to rotate, greenish-yellow, becoming vinaceous to the apex, abaxially glabrous, adaxially glabrous within the tube, pubescent on the lobes, more densely along the throat; tube 1.9–2.5 × 2.0– 2.4 mm; lobes 2.6–3.2 × 1.7–2.2 mm, ovate, recurved, apex acute to attenuate, margins not ciliate ( Figs. 1C, D , 2E ). Corona lobes 1.45–1.6 × 0.85–1.1 mm, a lower portion auriculate, adnate to the anther dorsum, an upper portion ovate-elliptic, free, incurved, not reaching the style-head apex ( Figs. 1E, F ). Gynostegium ca. 3.2 mm high, stipitate (stipe ca. 1.0 mm high); style-head 1.6–2.3 × 0.65–1.0 mm, conical, bilobed, exserted from the corolla tube; anthers ca. 0.24 × 0.15 mm, apical membranous appendix 0.62–0.7 × 0.81–0.9 mm, quadrangular; corpusculum 0.28–0.33 × 0.1–0.12 mm, oblong, apex obtuse to rounded; caudicles 0.13–0.18 mm long; pollinia 0.21–0.29 × 0.1– 0.14 mm, ellipsoid to obovoid, erect ( Fig. 1G ). Follicles ca. 16 × 3.6 cm, oblong-elliptic, glabrous ( Figs. 1H , 2F ).

Etymology: The name of this new species highlights its distribution, restricted to the Bahia state.

Notes: Ruehssia bahiensis is characterised by elliptic to ovate leaves ( Figs. 1A , 2C ) and corymbose inflorescences ( Figs. 1B , 2D ). The flowers feature ovate sepals and greenish-yellow campanulate to rotate corolla, adaxially pubescent on the throat and lobes ( Figs. 1C, D , 2E ). The corona lobes are ovate-elliptic to triangular, with a lower auriculate portion and do not reach the style-head apex ( Fig. 1F ). The style-head apex is conical ( Fig. 1E ) and exerted from the corolla tube ( Figs. 1D , 2E ).

Ruehssia bahiensis resembles R. pickelii . Both species are lianas with elliptic leaves and corymbose inflorescences. Their greenish flowers have recurved corolla lobes, and the corona lobes exhibit an auriculate lower portion and an ovate-elliptic to triangular upper portion. Nonetheless, the new species can be promptly distinguished from R. pickelii by the corolla lobes adaxially pubescent (vs glabrous in R. pickelii ) and the style-head conical (vs subglobose), longer than (vs as long as) the corona ( Tab. 1 ).

Phenology: The new species has been collected with flowers in November, during the late spring, and was seen with fruit in June (Gildasio Oliveira dos Santos, pers. comm.).

Distribution and habitat: Ruehssia bahiensis is distributed within the Semi-arid region of northeastern Bahia associated with the Depressão Sertaneja Meridional ecoregion of the Caatinga domain ( Velloso et al. 2002). It is known from only three municipalities, growing in rocky outcrops and shrubby caatingas surrounded by degraded vegetation ( Fig. 2A, B ). Ruehssia pickelii is also endemic to the Brazilian Semi-arid region but occurs in Pernambuco, Paraíba and Rio Grande do Norte states, growing exclusively in shrub-arboreal caatinga vegetation ( Fig. 3 ).

Conservation status: Ruehssia bahiensis has an extension of occurrence (EOO) of 4.342 km 2 and an area of occupancy (AOO) of 12 km 2, suggesting that the new species should be classified as Endangered: EN [B1ab (i, ii, iii) + 2 ab (i, ii, iii)], according to the criteria of the Red List of the IUCN (2019). The new species grows close to roads and rural properties, in areas significantly transformed by human activities, and faces a clear risk of extinction within its known distribution area.

The type collection of this new species was obtained within the sisal territory region, just at the top of the Serra do Pintado in Valente municipality. The sisal territory comprises 20 municipalities, with sisal ( Agave sisalana Perrine ex Engelmann 1875: 305 , 316) as a prominent economic and cultural resource ( Bahia 2016). This xerophytic species is not native to the Brazilian flora and has notably impacted the region’s original vegetation cover ( Carvalho et al. 2023).

Historically, the sisal territory has been overlooked in floristic studies, primarily restricted to Tucano municipality ( Cardoso & Queiroz 2007; Costa et al. 2015). Recently, some of us concluded an inventory of land plants in the Serra do Mucambo in Conceição do Coité, approximately 50 km from the type locality of R. bahiensis . This area holds a high plant diversity and has the potential for implementing the first formal conservation unit in the region ( Carvalho et al. 2023). While samples of this new species have not yet been collected in the Serra do Mucambo , four other Apocynaceae species have been found in this location, including R. altissima ( Jacquin 1760: 17) F. Espírito Santo & Rapini (2019: 10) ( Carvalho et al. 2023), widely distributed in South America (Espírito-Santo et al. 2019, 2023).

Similarly, the region of Feira de Santana remains relatively underexplored floristically, and we found only one collection of R. bahiensis from this area. This region lies in a transitional zone between seasonally dry forests and woody and coastal tropical forests ( Rizzini 1963; Cardoso et al. 2009) and lacks conservation units. Studies on its local flora are scarce, mainly restricted to fragments of semideciduous forests in transitional zones between Caatinga and Atlantic Forest domains ( Cardoso et al. 2009; Anunciação 2022). The discovery of this new species endemic to the Semi-arid of Bahia within this region highlights the urgent need for comprehensive surveys in this poorly studied yet potentially rich flora.

In conclusion, the new species R. bahiensis underscores the significance of further floristic investigations in Bahia’s Semi-arid region for enhancing our understanding of native species. Disseminating this finding to local communities and guiding effective conservation policies is paramount, given the historical suppression of native vegetation, predominantly due to pastures and agricultural land conversion. These regions show the potential to harbour a rich flora, including rare, endemic and threatened species. Additionally, several native species in these regions are beneficial for human purposes and warrant heightened attention from a conservation standpoint.

Additional materials (paratypes): BRAZIL. Bahia: Feira de Santana, 12º15’20”S, 39º04’59”W, 02.XI.2015, fl., E. Melo et al. 13177 ( HUEFS) ; Araci, 11º17’34”S, 38º55’25”W, 29.XI.2018, fl., A. Rapini 2096 ( HUEFS) ; Valente, 11º17’56”S, 39º28’43”W, 01.XI.2021, fl., I.C. Oliveira et al. 63 ( HUEFS) .

Figures

FIGURE 1. Ruehssia bahiensis. A branch with leaves, B inflorescence, C flower, seen from above, D flower, lateral view, E flower, perianth removed to show the corona in front of gynostegium, F corona lobe, frontal view, G pollinarium, H fruit. (A-G: Oliveira 13; H: from Araci, Fig. 2F). Illustrated by Pétala Ribeiro.

FIGURE 2. Ruehssia bahiensis. A environment of occurrence, B, C habit, D inflorescences, E flower, seen from above, F fruit (C: I.C. Oliveira 13; D, E: Rapini 2096). Photos: A, C by MCD; B, D, E by AR and F by Gildasio Oliveira dos Santos.

FIGURE 3. Geographical distribution of Ruehssia bahiensis and R. pickelii.