Acianthera nukiniana Marcusso & Biral & Demarchi & Zartman 2026, sp. nov.

Acianthera nukiniana Marcusso sp. nov. urn:lsid:ipni.org:names:77376848-1 Figs 4–5 Diagnosis Acianthera nukiniana sp. nov. resembles A. silvae (Luer & Toscano) Luer by the erect stem, lamina linear, 2-flowered inflorescence, lateral sepals connate up to the upper third, and lip with two lateral lobes, but differs by the habit caespitose (vs the repent in A. silvae), petal margins pilose, mainly toward the apex (vs microscopically denticulate), densely papillose in the apex (vs smooth), and shorter lip (1.5 mm vs 2.75 mm long) with near equal length of the column (vs exceeding the column length). Etymology The name refers to the Nukini people, that historically lived in the high Rio Moa, in the Juruá basin (Oppenheim 1936), where P. nukiniana sp. nov. was recorded. Today, they still live in the region, along the border with the SDNP, in the Indigenous Land Nukini (Correia 2024). Type material Holotype BRAZIL • Acre, Mâncio Lima, Parque Nacional da Serra do Divisor, trilha para a cachoeira da Formosa, cerca de 8 km do início; 07°20′58″ S, 73°41′25″ W; 370 m a.s.l.; 23 Nov. 2024; Marcusso, G.M., Demarchi L.O., Biral, L., Zartman, C.E., Magalhães, J. 2799; holotype: RB [01578436]. Description Epiphytic herb, erect, ca 10 cm tall, caespitose, rhizome with internodes ca 1 mm long, 1.4 mm wide. Stem cylindrical, sulcate, 3.1 to 3.8 cm long, 1 mm wide, with a tubular sheath up to the middle, brownish, apex acute. Leaf sessile, lamina carnose, 5.5 to 6.5 cm long, 5.6 to 6.3 mm wide, linear to oblanceolate, base attenuate, apex acute, margin revolute. Inflorescence multi-flowered, coflorescences 2-flowered, peduncle ca 8 mm long, enclosed by a conduplicate, lanceolate bract with 3 mm long, ca 0.3 mm wide, green, with apex attenuate, rachis abbreviated ca 0.5 mm long, floral bract tubular, 1.4 mm long, ca 0.3 mm wide. Ovary ca 2 mm long, glabrous, cylindrical, slightly grooved. Flowers tubular, ca 5 mm long. Sepals pink, glabrous, dorsal sepal oblong, with acute apex, 5 mm long, 2 mm wide, 3-veined, lateral sepals connate up to the middle, at ca 3 mm long, elliptic, apex acute, 6.2 mm long, 2 mm wide. Petals pink-whitish, oblong, with acute apex, 2.6 mm long, 0.8 mm wide, 1-veined, margin ciliate, mainly towards the apex, surface in the apex densely papillose. Lip pink-whitish, sessile, oblong, trilobed, recurved, 1.5 mm long, 0.8 mm wide, apex rounded, two lateral lobes erect, recurved, apex papillose. Column pink-white, semi-terete, recurved, ventrally channeled, winged, 1.6 mm long, 0.8 mm wide, apical margin slightly denticulate, foot ca 0.8 mm long, anther oblong, glandular-papillose, surrounded by the clinandrium, ca 0.3 mm long, 0.5 mm wide, pollinarium with two ovoid pollinias, ca 0.3 mm long, attached to a caudicle, apical margin slightly irregular. Capsule not seen. Distribution, habitat and phenology Acianthera nukiniana sp. nov. is known only from the SDNP, in Acre State (Fig. 1). This species occurs as an epiphyte in low densities in lowland dense ombrophilous forests, locally known as terra firme, at an elevation of 370 m. Collected with flowers in November. Preliminary IUCN conservation assessment Acianthera nukiniana sp. nov. has been identified in only one location, where few mature individuals were observed, but similar habitats are found extensively throughout the region (Mendonça et al. 2020), suggesting that new populations can be found. The trail to Formosa Waterfall, lies within the SDNP, a protected area surrounded by several conservation areas, including the Alto Juruá Extractive Reserve and the Nawa and Nukini Indigenous Lands in Brazil, as well as the Sierra del Divisor National Park in Peru. Nevertheless, the region faces serious threats, including the growth of livestock farming and the proposed extension of the BR-364 highway, which would intersect the area (Koga et al. 2022). Due to insufficient data on its distribution and population size, we suggest classifying Acianthera nukiniana as Data Deficient (DD) under the IUCN Red List Categories (IUCN 2024). Remarks Acianthera nukiniana sp. nov. is morphologically similar to A. silvae, which is known only by the type from Japura River, in the State of Amazonas (Luer & Toscano de Brito 2002), with several floral differences (see diagnosis). Also resembles A. punicea (Luer) Pridgeon & M.W.Chase, from Ecuador, differing by the sessile lip (vs unguiculate in A. punicea), trilobate (vs not trilobate) and shorter (1.5 mm vs 3 mm long); and A. carinata (C.Schweinf.) Luer, from Peru, differing by the caespitose habit (vs repent), shorter sepals (5 to 6.2 mm vs ca 10 mm long), lip shorter (1.5 mm vs ca 5 mm long), and apical lobe of the lip rounded (vs acute). Acianthera nukiniana sp. nov. putatively belongs to the Acianthera subgenus Acianthera by the stout habit, sulcate stem, fleshy flowers, lateral sepals fused, concave, margin slightly denticulate, and lip thick (Karremans et al. 2016), and to the Acianthera section Acianthera (sensu Chiron & van den Berg 2012).