Endemic orchids of peninsular India: a review
Jeewan Singh Jalal 1 & J. Jayanthi 2
1,2 Botanical Survey of India, Western Regional Centre, 7, Koregaon Road, Pune, Maharashtra 411001, India
Email: 1 firstname.lastname@example.org (corresponding author), 2 email@example.com
Orchidaceae is one of the most ecologically and morphologically diverse families of flowering plants. It is the second largest family of flowering plants in the world, comprising of about 779 genera and 22,500 species (Mabberley 2008). They have diverse habits with variously modified vegetative and floral structures. Based on their varying habits, orchids are classified as holomycotrophic or saprophytic (growing on dead and decaying matter), terrestrials (growing on ground) and epiphytic (growing on trees or shrubs). They are very sensitive to habitat degradation and fragmentation. In India, the orchid diversity is represented by 1,331 species belonging to 186 genera (Misra 2007).
The Indian subcontinent has diverse climatic regimes, forest types and habitat conditions that provides a favourable environment for accommodating diverse life forms and species. Being separated by high mountain ranges of the Himalaya in the north and in the south by Arabian Sea, Bay of Bengal and Indian Ocean, the isolation of Indian flora to a large extent helps in the evolution of endemic taxa (Nayar 1996). Geologically the drifting of the Indian subcontinent from the Gondwanaland through various latitudes lead to immigration and extinction of species which are engraved in the present day floristic composition (Axelrod 1971). The endemism in the flora of a country or geographical region provides an important insight into the biogeography of that region and also to the centers of diversity and adaptive evolution of the floristic components of that region (Nayar 1996). In India, the peninsular region has a high degree of endemism making it the second richest endemic centre after the Himalaya. Nayar (1977) surmised, the history of flora of peninsular India is one of the floristic impoverishments due to flow of Deccan lavas during cretaceous-eocene time and spreading aridity in Miocene-quaternary period, causing depletion of its characteristic flora leaving few relict taxa. The peninsular region is a part of Indian plate of Gondwanaland and most of the endemic plants of this region are palaeoendemics. A large concentration of endemic species is found in the tropical moist deciduous and tropical semievergreen patches of Western Ghats and to a much lesser degree in Eastern Ghats (Nayar 1996).
Materials and Methods
Peninsular India comprises of seven states viz., Andhra Pradesh, Goa, Karnataka, Kerala, Maharashtra, Odisha and Tamil Nadu and one union territory namely Pondicherry. It is bound by Vindhyan Mountains in the north, Arabian Sea in the west, Indian Ocean in the south and Bay of Bengal in the east. The geography of the region can be divided into three zones namely the Deccan Plateau, Eastern Ghats and the Western Ghats (Image 1). The Deccan Plateau is the largest plateau in India, making up the majority of the southern part of the country. Eastern Ghats forms a broken chain of hill ranges extending through the states of Odisha, Andhra Pradesh and Tamil Nadu. It runs north-east to south-west direction in peninsular India. Western Ghats starts near the border of Gujarat and Maharashtra, south of the Tapti River and runs approximately 1600km through the states of Maharashtra, Goa, Karnataka, Tamil Nadu and Kerala ending at Kanyakumari. It is also one of the 34 Biodiversity Hotspots of the world (Myers et al. 2000). The vegetation type of peninsular India varies from tropical evergreen forest, tropical semievergreen forests, sholas, moist deciduous forests, dry deciduous forests, scrub jungles and dry savannah forests.
For the present analysis information on the endemic orchids of peninsular region was collected from literature such as Hooker (1888–1890), Blatter (1928), Fischer (1928), Cooke (1958), Santapau & Kapadia (1966), Saldanha & Nicolson (1976), Pradhan (1976), Bose & Bhattacharjee (1980), Yoganarasimhan et al. (1981), Nayar et al. (1984), Rathakrishnan & Chitra (1984), Rao (1986, 1998), Joseph (1987), Ahmedullah & Nayar (1987), Chandrabose & Nair (1988), Manilal (1988), Henry et al. (1989), Ansari & Balakrishnan (1990), Keshavamurthy & Yoganarasimhan (1990), Kumar & Manilal (1994), Lakshminarasimhan (1996), Nayar (1996), Pullaiah (1997), Karthikeyan (2000), Gopalan & Henry (2000), Mishra & Singh (2001), Singh et al. (2001), Kumar et al. (2001), Yadav & Sardesai (2002), Rao & Kumari (2003), Manilal & Kumar (2004), Sardesai & Yadav (2004), Joshi & Janarthanam (2004), Gaikwad & Yadav (2004), Misra (2007), Misra et al. (2008), Nayar et al. (2008), Bachulkar (2010) and Narayanan et al. (2010). The online databases, namely, Govaerts et al. (2012) http://apps. Kew.org/wcsp, Tropicos (2012) www.tropicos.org, IPNI (2012) www.ipni.org, eFloras (2012) www.efloras.org were also consulted for recent updates on the plant names and distribution. Species earlier recorded as endemic but now reported from the other parts of the world, were excluded from the current list and their nomenclatural changes were also updated. The endemic orchid species are listed based on phytogeographical regions and state-wise distribution is also provided. The present work is our modest attempt to give an up-to date account of the endemic orchids of the peninsular region and to include nomenclature changes, new distributional records and new species records.
Ahmedullah & Nayar (1987) brought out the first authentic work on the endemic plants of peninsular India and estimated 123 species and 33 genera of endemic orchids from this region. While Nayar (1996) estimated 136 species, later on Kumar & Manilal (1994) recorded 142 species belonging to 38 genera. Further, Rao (1998) estimated 126 endemic species. Singh et al. (2001) recorded 135 species and Misra (2007) recorded 160 species. So far the total endemic orchids in India are 404 (2.3%) (Misra 2007) out of 17,500 total flowering plants, peninsular India represents 39.6% of endemic orchids out of 1,331 total number of orchids.
The present analysis resulted with a total of 130 species belonging to 38 genera endemic to peninsular India (Table 1). Of these, 43 are terrestrial, 85 are epiphytic and two are holomycotrophic. The analysis shows that the genus Habenaria (25 spp.), Oberonia (17 spp.), Bulbophyllum (15 spp.), Dendrobium (11 spp.) and Eria (6 spp.), are among the species rich genera representing nearly 60% of total endemic orchids of peninsular India. The Western Ghats region has maximum 123 endemic orchid species followed by Deccan Plateau and then Eastern Ghats (Fig. 1). Of the total endemic orchid species of the peninsular region, 95 (73%) are strict endemics to Western Ghats and five species (4%) are restricted to Eastern Ghats. However, there are no strict endemic species in the Deccan Plateau (Fig. 1). A state wise analysis of distribution of endemic orchids shows that Kerala has a maximum number of endemic species followed by Tamil Nadu, Karnataka and Maharashtra. The states of Gujarat, Andhra Pradesh and Odisha show very poor representation of the endemic species (Fig. 2). A total of 27 orchid species earlier considered as endemic to the peninsular region are excluded from the list owing to their extended distribution in the neighbouring countries (Table 2).
Endemic taxa occur in a restricted area usually isolated by geographical or temporal barriers (Ahmedullah & Nayar 1987). The endemic taxa occurring in such isolated/restricted areas are possible survivors of their ancient stock that occurred in continental areas which were subjected to cataclysmic geological and climatic changes (Nayar 1996). The major concentrations of endemic orchid species are found in the Western Ghats (Subramanayam & Nayar 1974). Agasthyamalai Hills, Anamalai-High Ranges, Nilgiris-Silent Valley-Waynad-Kodagu region, Shimoga-Kanara, Mahabaleswar-Khandala and Konkan-Raigad are some of the important centers of endemism in the Western Ghats. Ninety five endemic orchid species are particularly restricted to these areas. Eastern Ghats have geological antiquity with isolated mountain ranges. The Eastern Ghats have some Ňecological islandsÓ that harbor endemic orchids. These are Ganjam-Koraput range in Odisha, Visakhapatnam Hills, Nallamalai-Cuddappah range and Tirupati Hills of Andhra Pradesh. Though Eastern Ghats possess a few rich forest patches, it has been poorly explored floristically as compared to Western Ghats. Eria meghasaniensis (S. Misra) S. Misra, Habenaria panigrahiana S. Misra, Habenaria panigrahiana var. parviloba S. Misra, Odisha cleistantha S. Misra and Zeuxine lindleyana A.N. Rao are strictly endemic to Odisha State. Aerides maculosa Lindl., Bulbophyllum kaitiense (Wight) Rchb.f., Dendrobium aqueum Lindl., Dendrobium ovatum (L.) Kraenzl., Eulophia ochreata Lindl., Habenaria crassifolia A. Rich., Habenaria foliosa A. Rich., Habenaria grandifloriformis Blatt. & McCann, Habenaria hollandiana Santapau, Habenaria rariflora A. Rich., Oberonia brunoniana Wight, Oberonia proudlockii King & Pantl., Oberonia santapaui Kapadia, Oberonia verticillata Wight and Schoenorchis jerdoniana (Wight) Garay have very wide distribution in the peninsular region.
The endemic orchids of the peninsular region are facing various kinds of localized threats like livestock grazing and forest fires as well as landscape-level threats such as mining, construction of roads, large as well as micro-hydal power projects, wind farms, large-scale agricultural expansion and creation of monoculture plantations. To cite an example Paphiopedilum druryi (Bedd.) Stein. which was once found in plenty in Agastyamalai Hills in southern India is now difficult to locate.
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