Aristolochia rethyae S. Kashung, Rimi Barman et P. R. Gajurel, 2022

Kashung, Soyala, Gajurel, Padma Raj, Singh, Binay, Barman, Rimi & Yakang, Tage, 2022, Aristolochia rethyae, a new species from Arunachal Pradesh, north-east India, Phytotaxa 564 (1), pp. 1-7 : 2-4

Aristolochia rethyae S. Kashung, Rimi Barman et P. R. Gajurel , sp. nov. (Fig. 1 & 2).

Aristolochia rethyae is morphologically close to A. griffithii and A. tanzawana (Kigawa) Watan. -Toma & OhiToma (2014:160) in its leaf texture which is densely pubescent abaxially, and the perianth limb being shallowly 3- lobed. However, it can be distinguished very easily from A. griffithii in its ovate to narrowly ovate leaves, cauliflorous inflorescence, pubescent perianth and capsule texture. It is also distinctly different from A. tanzawana in its cauliflorous inflorescence, S-shaped perianth and much larger capsule with distinct wavy ridges.

Type:— INDIA. Arunachal Pradesh: Papum Pare district, Kimin forest , 27°20’26.1276”N, 93°59’2.4756”E, elev. 195 m, 17 November 2021, Soyala K. et al.190 (holotype CAL! isotypes ARUN! NERIST!)

Perennial, semi-woody liana, 10–15 m high, twining dextrorse. Stem cylindrical, mature stem glabrescent, bark corky, furrowed longitudinally, young stem densely pubescent. Petiole 6–7 cm long, densely pubescent. Leaves simple, alternate, lamina ovate to narrowly ovate, 10–15 × 9–10.5 cm, chartaceous, abaxially pubescent, adaxially pubescent along the veins, margin entire, apex acuminate, base cordate, sinus 2.5–3 cm deep, 2–2.5 cm wide, auricles rounded, basal veins palmately 3-nerved, prominent. Inflorescence cyme on old woody stem, fasciculate, each cluster with 2–16 cymes, with 3 or 4 flowers in each axis, axis ca. 10–14 cm long, densely pubescent. Bracteoles small, triangular, 0.2–0.3 × ca. 0.2 cm, densely pubescent. Pedicel slender, 2–3 cm long, densely pubescent. Perianth S-shaped, ca. 3–3.5 × 2.5–3 cm, tubular, abaxially densely villous, adaxially glabrous. Utricle not sharply delimited with perianth tube, 0.8–1 cm high, 0.5–0.6 cm diam. at base, 0.4 cm diam. at apex, inside with dark purple band towards the base, and densely distributed trichomes. Tubes geniculately curved at middle, curving upward, 1–2 × 0.5–0.6 cm. Limb 3-lobed, disc-shaped, 2.5–3 cm wide, margin slightly recurved, apex acute, yellowish green with dark brown striation, throat colour same as limbs, circular, annulus 0.8–1.2 cm wide. Gynostemium 3-lobed, 0.7 × 0.4 cm, lobes with rounded apices. Stamen 6, sessile, anther bilobed, oblong, ca. 0.4 × 0.1 cm, adnate in pairs in the gynostemium lobes. Ovary elongated, 1–1.5 × ca. 0.2–0.3 cm, 6-ridged, densely brown tomentose, stipe absent. Capsule linear-elliptic, 15–17 × ca. 2.8–3.2 cm, apex stipitate, distinctly 6 longitudinal and wavy ridges, yellowish green and covered with dense dark brown hairs.

Etymology: — The specific epithet honors Dr. Parakkal Rethy, former Professor of Department of Forestry, North Eastern Regional Institute of Science and Technology, Arunachal Pradesh, India, for her contribution to the field of Angiosperm taxonomy.

Phenology: —Flowering from October to December and fruiting from December to April.

Distribution and ecology: — Aristolochia rethyae is currently known only from one population in the forest of Kimin area, Papum Pare district, Arunachal Pradesh, India. It grows near the roadside in a humid area in a tropical evergreen forest at around 195 m elevation. Only a single mature plant with flowering and fruiting was observed, twining on a Ficus species and growing in association with Dipterocarpus retusus Blume (1823: 77) , Alstonia scholaris (L. 1767: 53) R. Br. (1810: 65), Gmelina arborea Roxb. (1814: 46) , Magnolia pterocarpa Roxb. (1820: 62) , Piper acutistigmum C.DC. (1925: 196) , Phrynium pubinerve Blume (1827: 38) , and Diplazium esculentum (Retz. 1791: 38) Sw. (1801: 312) . Additionally, about 10 immature individuals were observed nearby within a radius of 100 m.

Conservation status: — The habitat of the species being on the roadside is highly disturbed. It was observed that the forest area near the new species has recently been cleared for road construction, thereby imposing high threats to the population. As the species is growing with a limited population in a highly disturbed area, there is a high risk of complete habitat destruction and hence warrants an immediate conservation effort. It may be considered a Critically Endangered (CR) by applying the IUCN criteria B1a, B2a, and D ( IUCN, 2001). The authors are trying to impart awareness to the local communities of nearby areas and are also growing the plant in the NERIST campus through collections of seeds.

Taxonomic notes: — Morphologically, the new species described here resembles A. griffithii by having similar leaf texture, limb shape, and capsule shape, but differs from the latter by the morphology of the leaf lamina, inflorescence, perianth texture, and capsule texture. The new species is also similar to A. tanzawana with respect to the perianth texture, limb shape, and capsule texture, but differs in their inflorescences, perianth shape, capsule size, and capsule ridges. A more detailed analysis of character similarity and differences is given in Table.