Asia has the world's highest and most populous mountain chain, the Himalaya. Among the Himalayan Mountains, the Indian Himalayan Region (IHR) is known for its diverse biodiversity. The IHR covers 11 states (09 entirely & 02 partially) and two Union Territories (Jammu and Kashmir and Ladakh). The region accounts for approximately 4% of India's total population (48.6 million), 16.2% of total land mass (5,33,604 km2), 36% of total forest cover (2,50,708 km2) and 63% of total waterflow budget. It supports over 50% of all blooming plants in India, with 30% of the flora being indigenous. The region has been classified as one of 36 global biodiversity hotspots, with significant ecological and economic value on the one hand and evidences of accelerating biodiversity loss on the other. This region's biodiversity wealth benefits people's livelihoods both directly and indirectly through a variety of ecosystem products and services, including the most desirable carbon sink. However, societal pressure combined with natural disasters has placed numerous species on the list of threatened species.

All of these estimations indicate that there is an urgent need to establish conservation and sustainable utilization plans for Himalayan biodiversity. We have a lot of information on plant biodiversity in the IHR, but we lack comprehensive inventory of the reported species in various lifeforms in the region. NMSHE-TF 3 is developing a complete database of plants in different life forms in the region.

Under this mission, we have curated an updated checklist of pteridophyte flora and their distribution across the IHR by conducting a thorough analysis of 367 research works published between the 1870s and 2020s as books, floras, manuals, reviews, checklists, and articles. In order to incorporate more pteridophyte taxa distributed in the IHR, we also screened the pertinent references of the compiled sources, which were then further enhanced with online sources such as Plants of the World Online (POWO 2024) (https://powo.science.kew.org/), India Biodiversity Portal (https://indiabiodiversity.org/), and eFloras of India (https://efloraindia.bsi.gov.in/; https://efloraofindia.com/). We standardized the taxonomic names of the taxa in accordance with Plants of the World Online (https://powo.science.kew.org/) in order to examine the numerous species entries due to synonymy.

We also screened the references of the related published papers to look for additional species records from the region.
1. We recorded a total of 964 species, 49 sub-species and 12 varieties of pteridophytes in the IHR belonging to 106 genera in 19 families. Among these, there were 923 ferns (866 species, 47 subspecies and 10 varieties) under 95 genera in 13 families and 102 fern-allies (98 species, 2 subspecies and 2 varieties) under 11 genera in 6 families. Of the total documented pteridophytes, 77% of the taxa belonged to Polypodiaceae (343 species, 9 subspecies and 4 varieties in 33 genera), Aspleniaceae (246 species, 26 subspecies and 4 varieties in 19 genera) and Pteridaceae (148 species, 10 subspecies and 1 variety in 15 genera).

2. The regional distribution of pteridophytes exhibited considerable variation across the IHR, with higher number of taxa documented from east Himalaya (840 taxa in 98 genera and 19 families) as compared to west Himalaya (528 taxa in 81 genera and 18 families) (Figure 1). Among the states and union territories which are part of the Indian Himalayan Region, maximum number of pteridophytes were documented in Arunachal Pradesh (590 in 91 genera and 18 families), followed by Assam (535 in 87 genera and 17 families) and Sikkim (521 in 86 genera and 17 families). The Jaccard similarity index (J), calculated between pairs of the states/UTs, ranged from 0.025 (Ladakh-Mizoram) to 0.66 (Jammu & Kashmir-Himachal Pradesh) (Figure 2a). There was an apparent decrease in similarity when pairing west with east Himalayan states, with Ladakh having lowest similarity indices with all of them (Figure 2a). A hierarchical cluster analysis based on the similarity index grouped the states/UTs across IHR into four clusters with regions having compositional similarity among pteridophyte flora grouped together (Figure 2b).

3. While a significant proportion of pteridophytes exhibited more than one type of habit (nearly 30% taxa), maximum number of taxa were found to be terrestrial (770 taxa), followed by epiphytes (308 taxa). Moreover, moist shaded slopes/areas and forest floors types of habitats inhabited a major proportion of pteridophytes (882 taxa), followed by river or stream banks and marshes (630), while minimum richness was observed in disturbed sites (burned forests or grasslands) and roadsides (68 taxa).

4. Based on the nativity of flora, a total of 756 species, 39 subspecies and 04 varieties distributed 97 genera and 19 families were native to the Himalayan region. Among these, 679 species, 38 sub-species and 4 varieties were ferns under 86 genera and 13 families, while 77 species and 2 subspecies were fern-allies under 11 genera and 6 families. The dominant families were Polypodiaceae (288 taxa in 30 genera) and Aspleniaceae (216 taxa in 17 genera) contributing 63% of the native pteridophyte flora. Among these, nearly 40% (412 taxa in 75 genera and 15 families) of pteridophytes were having their native range restricted to east Himalayas, while only 10% (107 taxa in 22 genera and 9 families) were exclusively native to west Himalayas. The highest number of pteridophytes native to the Himalayas were documented in Arunachal Pradesh (524 taxa in 88 genera and 18 families), followed by Sikkim (465 taxa in 84 genera and 17 families) and Assam (448 taxa in 82 genera and 17 families).

5. As per the IUCN Red list of threatened plants (2022), a total of 91 species, 7 subspecies and 1 variety distributed in 42 genera and 16 families are grouped into various threat categories (Critically endangered, CR; Endangered, EN; Vulnerable, VU; Near Threatened, NT; Data deficient, DD; Rare, R; Least concern, LC) (Table 2). Among the threatened flora, population status of sixty-eight taxa were documented by IUCN (2022), i.e., population of three species was increasing, forty-eight was stable and seventeen was decreasing. Among the recorded taxa, a total of 209 species, 3 subspecies and 3 varieties distributed in 70 genera and 19 families are used for multifarious medicinal and therapeutic purposes by the local inhabitants across IHR. Majority of the medicinal flora were ferns (84%; 180 were ferns), while 16% (35) were fern allies. Assessing the endemic status of the documented pteridophytes revealed 12 taxa (9 ferns and 3 fern-allies) belonging to 7 genera and 3 families were endemic to IHR.