Extended distribution and assessment of conservation status of Impatiens exilis Hook . f . ( Balsaminaceae ) an endemic species of Eastern Himalaya

The present communication reports an extended distribution of Impatiens exilis Hook. f., in North Eastern part of India. The species is so far reported from Sikkim only in India and endemic to eastern Himalaya. Present collection of Impatiens exilis Hook. f., from Panbari Range, Manas National Park, Assam extends its distribution territory to Assam in the North-Eastern Part of India. The analysis of its threat status suggests that the species is an endangered (EN) one. A detailed description with phenology and photographs has been provided for easy identification of the species.


Introduction
Impatiens L. is one of the dominant angiospermic herbaceous genera of Balsaminaceae with more than 1000 species (1) found all over the wet and subtropical regions of Asia, Africa and a few in temperate regions of Asia, Europe and North America (2,3). In India, the genus is represented by about 250 species primarily distributed in the moist, mountainous region of Western Ghats, Eastern Himalaya and North-eastern states (4,5). During the study of floristic diversity in Manas National Park in Assam, the authors came across a set of interesting species (6)(7)(8) including a member of the genus Impatiens. After analysis of the specimens and inspection of the related literature (5,9,10) the plant was recognized as Impatiens exilis Hook. f., hitherto not recorded from any other states of (Arunachal Pradesh, Assam, Meghalaya, Manipur, Mizoram, Nagaland, and Tripura) of North Eastern India except Sikkim. Additional inspection of other relevant literature (2,(9)(10)(11)(12)(13) and herbarium specimens in the major Indian Herbaria (ARUN, ASSAM, BSHC and CAL) confirmed that the taxon is only reported from Sikkim in North East India. Hence, the present collection of Impatiens exilis Hook. f., from the Manas National Park, Assam extend its distribution beyond Eastern Himalaya and form an addition to the flora of Assam. The herbarium specimens are deposited at the Herbarium of Forest Department, Manas National Park and Department of Botany, Gauhati University for future reference. Details account of the taxon along with its photographs is provided. Furthermore, the grave threats of continued change in land use patterns and climate changes in the foothills of the Himalayas, assessment of threat status of biodiversity has appeared as a thrust field of research (14,15). Determination of the recent risk status of a species is vital in conservation, development of management action plan and drawing public attention towards the taxa (14,15). Being an endemic species, an assessment of the threat status of I. exilis across the Himalayas based on IUCN criteria (16,17) has also been carried out

Study area
Manas National Park (MNP) occupies an area of 500 sq. km and is located at the foothills of the Bhutan Himalayas in Baksa and Chirang districts, Assam, India in between 26°35'-26°50'N latitude and 90°45'-91°15'E longitude (Fig.  1). The National Park consists of three ranges namely -the Western Range with its headquarters at Panbari, the Central Range with its headquarters at Bansbari and the Eastern Range at Bhuyapara. The main vegetation types of MNP comprises of Sub-Himalayan light alluvial semievergreen forests in the northern parts, East Himalayan mixed moist and dry deciduous forests (the most common type), low alluvial savanna woodland and Assam valley semi-evergreen alluvial grasslands (7).

Methods
While floristic survey was carried out in MNP, Assam, India, individuals of Impatiens exilis were recorded from Panbari range in 2017. Comprehensive description of the species was made and herbarium specimens were prepared following the standard procedure (18). The identity has been confirmed by checking the protologue description and inspecting an image of the type specimen. The threat status of I. exilis was evaluated following IUCN versions 3.1 and 4.0 criteria B (geographical range) and D (population size) (16,17). Geo-coordinates of occurrence of the species were recorded and collected from other sources: (i) herbarium records (E, CAL & K) and (ii) records from Bhutan Biodiversity Portal (BBP, https://biodiversity.bt accessed 10 May, 2020). In case of herbarium specimens lacking geocoordinates, Google Earth TM was used for geo-referencing the herbarium label data. Based on the recorded geocoordinates of the present locality, type locality and other area of occurrences, the Extent of Occurrence (EOO) and Area of Occupancy (AOO) of the populations were assessed using the conservation assessment tool extension developed by the Royal Botanic Gardens, Kew (19) in Arc View. For AOO, a 2 × 2 km grid cell size was used. The pilot assessments thus generated for EOO and AOO were then subjected for comparison with the IUCN criteria for assigning the threat status of the species.

Habitat
Tropical moist rocky and shady slopes near the river bank. The habitation of the species is facing the risk of soil erosion

Threat status
Impatiens exilis is yet to be listed in the Red data book of Indian plants (20) and in the IUCN Red List (21). The populations of this taxon have been found living at a serious status at the forest edge along riverside. There are natural pressures like soil erosion in the habitat, which may completely eradicate the existing populations. Assessment of the risk status using IUCN versions 3.1 and 4.0 has also been carried out. We estimated the Area of Occupancy and Extent of Occurrence of the species as 44 Sq.km. and 47,447.96 Sq.km respectively (Fig. 3). During the last three years, we have also noticed a continuing decline in the quality and territory size of the habitat. Accordingly, we ranked the species as Endangered based on the B2 a &b (iii) IUCN Red List Categories and Criteria: Version 3.1.

Discussion
Although this North-Eastern Part of India has been aptly explored botanically many times by the different botanists since the period of Roxburgh (18,(22)(23)(24)(25)(26)(27)(28), none had reported the existence of this species from the region. Present records of I. exilis is a new addition to the flora of Assam, and represent an eastern ward distributional extension of this plant species in the Himalaya. The species I. exilis is found endemic to the Eastern Himalayan region with limited distribution and population and categorized as Endangered which warrants its conservation.