Checklist of the genus Dendrobium Sw. (Orchidaceae) in Manipur, India

: An enumeration of the genus Dendrobium Sw. (Orchidaceae) in Manipur, India was attempted. Literature review revealed the occurrence of 67 species under the genus from the state. The study was carried out through repeated field explorations in different natural forests of Manipur since 2012. Out of the total taxa reported from the state, only 42 species could be traced in the field. All these taxa are presented here with their flowering phenology and places of occurrence. Twenty-five species were untraceable in the field; however, nine species out of these 25 are represented by authentic herbarium specimens and supported by published documents. The remaining 16 species were reported only in literature, but no live plants or herbarium specimens were found. Out of the 42 species inventoried from the field, many taxa are under threat owing to habitat loss due to felling of trees, deforestation, and ‘jhum’ cultivation. So, there is an urgent need of conservation of those species through in situ and ex situ means for their sustenance. A p hotographic plate of some taxa is provided here which might be useful for their easy identification in the field and for taking care of their conservation. Large-scale uses of these species as cut flowers and indoor & outdoor plants may be practised through micropropagation and cultivation in nurseries which may help in revenue generation for the state


INTRODUCTION
The members of Orchidaceae Juss. are well known in the world for their beautiful and ineffable flowers of different colours, hues, and forms. Taxonomically, Orchidaceae is one of the most diversified and evolved families of flowering plants (Kumar & Manilal 1994). There is a vast range of diversity in the shape, colour, and size of orchid flowers; yet they are the same in their basic form (Pradhan 2005). Theophrastus (370-285 B.C.) named the group of bizarre plants as 'Orchids' finding resemblance of below-ground paired tubers with male testicles.
Dendrobium Sw. is the second largest genus of the family Orchidaceae after Bulbophyllum Thouars. It was established by Olavo (Peter) Swartz in 1799. The name was derived from the Greek words 'dendron' (tree) and 'bios' (life) which means 'one who lives on trees', or essentially 'epiphytes'. The genus is divided into 14 sections, viz.: Bolbidium, Callista, Dendrobium, Breviflores, Formosae, Stachyobium, Pedilonum, Distichophyllum, Rhopalanthe, Aporum, Oxystophyllum, Strongyle, Grastidium, and Conostalix (Seidenfaden 1985). The genus is sympodial with varying length of pseudobulbs. Most of the species are generally epiphytic or occasionally lithophytic in nature. They have adapted themselves to a wide variety of habitats starting from high altitudes to lowland tropical forests. They remain dormant during winter but quickly grow in summer. In spring, occasionally in autumn, dormant buds come out from the base of the pseudobulb followed by fast growth of new roots. Most of the Dendrobiums flower during the pre-monsoon season (March─May) and a few species blossom in the post-monsoon period. Capsules are produced late in the dry season (August─December).
The genus Dendrobium comprises about 3,160 species (Govaerts et al. 2022) with high morphological diversity and is mainly distributed in Sino-Himalayan regions with further extension up to Australia, New Zealand, and Pacific Islands (Wood 2006). In India, the genus is represented by c. 117 species (Rao 2022), of which, about 88 species are found in northeastern India (Rao 2018).

Study area
The state of Manipur, a part of Indo-Burma Biodiversity Hotspot, is bounded by Nagaland in the north, Mizoram in the south, Assam in the west, and Myanmar (Burma) in the east as well as in the south (Image 1). The state lies between the coordinates 23 0 83'-25 0 68' N and 93 0 03'-94 0 78' E. The total geographical area covered by the state is 22,327 km 2 . The total forest cover of Manipur is 17,219 km 2 , which is 77.12% of the total geographical area of the state. The state lies in a unique geographical position between the virtual meeting point of India and southeastern Asia (Singh 2014) with a total boundary of 854 km length. The altitude varies 50─3,000 m.
Based on the topography, structure, geology, the location's relief, and other geographical conditions, Manipur can be divided into two major natural physiographic divisions, viz.: (i) The Manipur hills and mountains and (ii) The Manipur valleys. Five major types of forests are prevalent in the state. These are: 1. Subtropical semi-evergreen forests, 2. Subtropical deciduous forests, 3. Montane wet temperate forests, 4. Subtropical pine forests, and 5. Subtropical dry temperate forests (Singh 2014).

Field survey and data collection
For the present study, several field explorations were conducted in different places of Manipur since 2012 (Table 1). Field surveys were made covering all seasons, although pre-monsoon and post-monsoon are the best collection seasons for the orchids especially for the genus Dendrobium. Locations were noted with their altitudes and geographical coordinates. A total of 58 sites were visited (Table 1). Surveys were conducted for at least 3-5 days at each location.

Identification of species
After collection, identification of species was done using standard methods of morpho-taxonomic studies. Flowers were dissected and critically studied under Stereo Zoom dissecting microscope (Olympus SZ61). Species without flowering were collected in a vegetative stage and grown in the nursery of the orchidarium of Centre for Orchid Gene Conservation of Eastern Himalayan Region (COGCEHR), Hengbung, Kangpokpi district, Manipur. These species were studied after they bloomed in the orchidarium. Morphological attributes were noted and identification of the species for all taxa were made using primary and secondary sources of  Table 1 is referred for locality names). Taxa

RESULTS
Out of the 14 sections of the genus Dendrobium (Seidenfaden 1985), species occurring in the state of Manipur are represented by eight sections (Table 2). In the field, the authors could locate only 42 species out of the 67 species recorded earlier from the state. Among these, 25 species could not be found in the wild, nine species are represented by herbarium specimens and    (Table 3) and 16 species were mentioned in literature without any representative specimens from Manipur (Table 4). All the collected species by the authors are presented here with their scientific and vernacular names, phenology, distribution in the state ( Table 2). Photographs of the species which are very rare in the field are provided to ease the identification of the taxa.
Among the 42 collected species from the state under eight sections, the dominant section was Dendrobium which was represented by 23 species. It was followed by the section Formosae (6 spp.), Callista (4 spp.), Stachyobium (3 spp.), Breviflores (2 spp.), and Pedilonum (2 spp.). Sections Aporum and Grastidium were found to be represented by a single species each. Some species like D. chrysanthum, D. chrysotoxum, and D. crepidatum were very common throughout the state. In contrast, D. bensoniae, D. capillipes, D. lindleyi, D. salaccense, and D. tamenglongense were rare in the study area in some localized pockets.

DISCUSSION
Manipur, a part of the Indo-Burma Biodiversity Hotspot (Myers et al. 2000), is one of the orchid rich states in northeastern India. Owing to its geographical location, serene forest cover, and humid climatic conditions, the state is blessed with rich plant genetic resources including orchids. Out of the 67 species reported from the state, only 42 species were seen in the field during this study. Further field surveys are needed to confirm the occurrence of the rest of the 25 species in the state.
Epiphytic Dendrobium species are found growing on trunks of small and large trees in tropical and

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