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

Acianthera amazonica Marcusso sp. nov. urn:lsid:ipni.org:names:77376847-1 Figs 2–3 Diagnosis Acianthera amazonica sp. nov. resembles A. saraca-taquerensis Campacci & J.B.F.Silva by the stem caespitose, erect, lamina linear-elliptic, with trilobed lip, but differs by the 4 or 5 flowers per inflorescence (vs 2 or 3 in A. saraca-taquerensis), lateral sepals with equal length of the dorsal (vs lateral sepals longer than the dorsal), apical lobe of the lip with margin fimbriate (vs margin slightly serrate), two callus in the lip (vs callus absent in the lip), and longer lip (3 mm vs 2.2 mm long). Etymology The name is in reference to the Amazon, where the species is apparently endemic. 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. 2801; holotype: RB [01578438]. Description Epiphytic herb, erect, ca 12 cm tall, caespitose, rhizome with internodes ca 0.5 mm long, 1.8 mm wide. Stem cylindrical, sulcate, 2.7 to 3 cm long, 0.9 mm wide, with a tubular sheath up to the middle, brownish with age. Leaf sessile, lamina carnose, 7.7 to 8.5 cm long, 1.2 mm wide, elliptical-lanceolate, base attenuate, apex acute, margin flat. Inflorescence multi-flowered, coflorescences with 4 or 5-flowered, peduncle ca 5 mm long, enclosed by a conduplicate, lanceolate bract with 3.5 mm long, green, with apex acute, rachis ca 6 mm long, covered by the floral bracts, which are tubular, green, 1.4 mm long, ca 0.8 mm wide. Ovary ca 2 mm long, glabrous, cylindrical, slightly grooved. Flowers tubular, ca 4.5 mm long. Sepals densely lilac-dotted, glabrous, dorsal sepals oblong, with acuminate apices, 5.8 mm long, 2 mm wide, 3-veined, lateral sepals connate to the upper third, ca 5 mm long, oblong, with apices slightly asymmetric, attenuate, 5.8 mm long, 2 mm wide, and adaxially with a central carina. Petals lilac-dotted, oblanceolate, with acute apex, 3.4 mm long, 1 mm wide, 1-veined, margin in the apices slightly irregular. Lip lilac densely in spots, oblong, trilobed, slightly recurved, unguiculate, 3 mm long, 1 mm wide, apex obtuse, with the apical lobe densely fringed, two lateral lobes erect, slightly rounded, two parallel longitudinal callus ca 1 mm long, slightly fringed towards the apex, central lip slightly papillose distally. Column densely lilac-dotted to whitish, semi-terete, slightly recurved, ventrally channeled, winged, 3.6 mm long, 1 mm wide, apical margin slightly denticulate, foot 1.3 mm long, anther sub globose, glandular-papillose, surrounded by the clinandrium, ca 0.5 mm long, 0.4 mm wide, pollinarium with two ovoid pollinias, ca 0.3 mm long, attached to a caudicle. Capsule not seen. Distribution, habitat and phenology Acianthera amazonica sp. nov. is currently known only from the State of Acre in the Serra do Divisor National Park (Fig. 1). It occurs as an epiphyte in low densities in Dense Lowland Ombrophilous Forests, locally known as terra firme, at 370 m of elevation. Collected with flowers in November. Preliminary IUCN conservation assessment Acianthera amazonica sp. nov. was found in only one locality with few conspecific individuals. Although the number of known populations and individuals is very limited, similar environments are widely distributed throughout the region (Mendonça et al. 2020) suggesting that its possible that the global range is larger than the study area. The type locality of the species, the Formosa Waterfall Trail, is located within a protected area – the SDNP, this park is surrounded by other 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. However, the region faces significant threats, such as the expansion of livestock farming and the proposed extension of the BR-364 highway, which would cross the area (Koga et al. 2022). Given the lack of information on its distribution and population size, we suggest categorizing Acianthera amazonica sp. nov. as Data Deficient (DD) according to the IUCN Red List Categories (IUCN 2024). Remarks Acianthera amazonica sp. nov. is morphologically similar to A. saraca-taquerensis, which is known only by the type specimen from the Guyana Shield, in Pará State, near the border with Guyana (ca 2000 km from the type locality of A. amazonica), differing by several vegetative and floral features, as mentioned in the diagnosis. Furthermore, although the color is variable in orchids, A. amazonica has sepals and petals densely lilac-dotted, differing from A. saraca-taquerensis which have yellow sepals and lip with purple spots and white-green petals. Acianthera amazonica sp. nov. putatively belongs to the Acianthera subgenus Acianthera due to its stout habit, sulcate stem, fleshy flowers, and thick, papilose lip (Karremans et al. 2016). By the lateral sepals fused, and the lip with two longitudinal calluses, Acianthera amazonica fits with the Acianthera section Acianthera of Chiron & van den Berg (2012).