Lysionotus namchoomii (Gesneriaceae), a new species from Arunachal Pradesh, India

Summary . The new species of the genus Lysionotus (Gesneriaceae), named L. namchoomii , discovered in Pakke-Kessang District of Arunachal Pradesh, India, is described and illustrated here. It differs from morphologically similar L. ziroensis mainly in glabrous vegetative organs, denticulate-crenulate leaf blade, deltoid inflorescence bracts, free spatulate glabrous calyx lobes, and corolla glabrous inside. This species is confined to two different locations, with a small population comprising a total of 60–100 individuals. The conservation status of this new species is provisionally assessed here as Critically Endangered, CR: B1a, b(iiii, v) + 2a, b(i-iii,v) following the IUCN Red List Categories and Criteria.


Introduction
The genus Lysionotus D. Don belongs to the subtribe Didymocarpinae D. Don, tribe Trichosporeae Nees ex Weber, subfamily Didymocarpoideae Arnott, and family Gesneriaceae Rich.et Juss., according to the recently established classification (Weber, 2004;Weber et al., 2011Weber et al., , 2013)), supported by molecular data (Ogutcen et al., 2021).The genus includes 34 accepted species (Mabberley, 2017;Taram et al., 2019), thirteen of which are reported from India (Sinha, Datta, 2016;Joe et al., 2017), including the recently described L. chatungii M. Taram, A. P. Das et H. Tag, and L. ziroensis Nampy, Nikhil, Amrutha et Akhil (Taram et al., 2019;Akhil et al., 2021).About 50 % of Indian species are endemic.Species of the genus are mostly epiphytic, lithophytic, or terrestrial evergreen erect or climbing subshrubs.They are well distinguished by their opposite or whorled leaves, funnel-shaped corolla with an inflated upper half, two stamens with connivent anthers, and appendaged seeds.The genus has broad distribution in continental SE Asia, spreading from Bhutan, Nepal, and S Japan to N Thailand, Laos, and N Vietnam (Möller et al., 2011), with the highest diversity in NE India and S China (Wang, 1983).All Indian species belong to the type section, L. sect.Lysionotus, according to the taxonomic system of the genus proposed by Wang (1983) and Li and Wang (2004).Species of this group have erect or ascending herbaceous stems, usually whorled leaves, a deeply divided calyx, and seed appendages as long as, or longer than, the seeds themselves.During the floristic studies of the years 2020 and 2021 in Arunachal Pradesh (Pakke-Kessang District), the first author collected a few unusual specimens of Lysionotus.The collected plants fit well with the characters of the type section but are surely different from all the known species of the genus, which have pendulous branches, 2-3 irregular, tuber-like swellings at the basal nodes, and glabrous leaves.Critical analysis of morphological characters, scrutiny of relevant literature, and herbarium specimens housed in BM, CAL, ARUN, and ASSAM clearly indicate that the collected specimens represent a hitherto undescribed taxon, which is described here as L. namchoomii.

Materials and Methods
The measurements and plant description are mainly based on living specimens.Studied herbarium specimens are stored at the Botanical Survey of India, Central National Herbarium, Calcutta (CAL), and Arunachal Pradesh Regional Centre, Itanagar (ARUN).All photos were taken in nature.Morphological characters were described using the terminology proposed by Harris J., Harris M. (2006), Hickey, King (2013), and Beentje (2016).Diagnosis.From the morphologically most similar Lysionotus ziroensis the new species differs mainly in glabrous stem, leaves, and peduncle; denticulate-crenulate leaf blade pale green below; Lysionotus namchoomii (Gesneriaceae), a new species from Arunachal Pradesh, India glabrous deltoid bracts; straight, spatulate, glabrous calyx lobes; and corolla glabrous inside.
Etymology.The species epithet honors the late Chau Phunkyoo Namchoom, a very popular figure as a social reformer representing the Khampti community in Arunachal Pradesh.He was a great nature lover and played a significant role in the upliftment of the Khampti community in Arunachal Pradesh, especially in facilitating good education and medical facilities for the people.
Phenology.Flowers in July-September; fruits in October-December.
Distribution and habitat.Presently, this species is confined only to Pakke-Kessang District, Arunachal Pradesh.However, exploration in adjoining districts may shed light on its exact range of distribution in the state.This species is found in evergreen forests and grows as an epiphyte or lithophyte.
Conservation Status.Lysionotus namchoomii is so far only known from two close locations in Pakke-Kessang District, where 60-100 mature individuals were observed.Formally, the species may be estimated as globally Critically Endangered, CR: B1a,b(iiii, v)+ 2a,b(i-iii,v).Available observations indicate that the species meets the following IUCN Red List categories and criteria (IUCN, 2023): only two populations were discovered, with the extent of occurrence (EOO) much less than 100 km 2 (B1a) and the area of occupancy (AOO) surely less than 10 km 2 in two known locations (B2a); observed and expected continuing decline (b) of the extent of occurrence (i), the area of occupancy (ii), area, extent, and quality of habitat (iii), and the number of mature individuals (v), when the populations are very small and highly fragmented, with the estimated number of mature individuals less than 100.

Fig. 1 .
Fig. 1.Lysionotus namchoomii: A -Flowering plant in natural habitat; B -Intact inflorescence; C -Flattened plant used for preparation of the type specimen; D -Rhizome; E -Inflorescence bracts; F -Calyx lobes, adaxial side; G -Intact flower, front view; H -Intact flower, side view; I -Opened corolla tube showing stamens; J -Pistil showing disc at the base.Photographed from the type materials by K. Chowlu, photo correction and plate design by K. Chowlu and L. Averyanov.