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STATUS OF PLANT DIVERSITY IN INDIA: AN OVERVIEW

W. Arisdason & P. Lakshminarasimhan

Central National Herbarium, Botanical Survey of India, Howrah

Introduction

India has a total geographical area of about 329 million hectares with a coastline of over 7500 km. The ecological or ecosystem diversity of the country is enormous, ranging from sea level to the highest mountainous ranges in the world; hot and arid conditions in the northwest to cold arid conditions in the trans-Himalayan region; tropical wet evergreen forests in Northeast India and the Western Ghats; mangroves of Sundarbans and fresh water aquatic to marine ecosystems (Sharma & Singh, 2000).

India has 12 biogeographical provinces, 5 biomes and 3 bioregion domains (Cox & Moore, 1993). The country supports a diverse array of habitats or ecosystems such as forests, grasslands, wetlands, coastal, marine and desert and each with rich and unique floristic diversity. These biological attributes are further enhanced by the geographic location of the country at the confluence of three major global biogeographic realms, viz. Indomalesian, Eurasian and Afro-tropical, thus allowing the intermingling of floristic elements from these regions as well and making it one of the 17 megadiversity countries in the world, recognised by the World Conservation Monitoring Centre in 2000. The floral diversity in India is majorly concentrated in the 4 biodiversity hotspots, namely Eastern Himalayas, Western Ghats (and Sri Lanka), Northeast India and Andaman Islands (Indo-Burma) and Nicobar Island (Sundaland), out of 34 biodiversity hotspots recognised in the world. These floristically significant areas exhibit exceptional concentration of endemic species and also experiencing loss of habitat with higher occurrence of threatened plant species.

Ecosystem Diversity

Forests, grasslands, wetlands, coastal and marine and desert are the major ecosystems in India. The forest cover of the country constitutes about 21.05% (692,027 km²) of India’s total geographical area (FSI, 2011). Champion & Seth (1968) have recognised 16 major forest types comprising 221 subtypes in the country. India has about 4.1 million hectares of wetlands (excluding paddy fields and mangroves). Mangroves in India cover an area of about 6700 km² constituting 7% of the world’s mangroves and represent one of the best swamps in the world. Coral reef, the other unique marine ecosystem in the country occurs in Andaman & Nicobar Islands, Lakshadweep Islands, Gulf of Kutch and Gulf of Mannar. The desert ecosystem covers about 2% of the total landmass (spreads over states of Rajasthan, Gujarat, Punjab and Haryana) in India, and is characterised by low precipitation and largely barren arid lands with only sparse or seasonal vegetal cover. The cold desert lies in Ladakh (Jammu & Kashmir) and in Lahaul-Spiti of Himachal Pradesh covers an area of about 1,09,990 km².

Species Diversity

Though the geographical area cover of the country represents about 2.4% of the world’s total landmass, it harbours a total of 47,513 plant species (Singh & Dash, 2014) out of about 0.4 million hitherto known in the world, representing as much as 11.4% of world flora. About 28% of plants that occur in India are endemic to the country. Table 1 represents a comparative account of species in major groups of plants, including virus, bacteria, algae, fungi and lichens recorded from India and the world. The table also provides approximate number of species considered endemic to India.

Table 1: Total number of plant species (including virus, bacteria, algae, fungi and lichens)

and their status in World and India

Source: Chapman, 2009; Singh & Dsah, 2014.

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Status of Plant species (including virus, bacteria, algae, fungi and lichens) in India

Angiosperms: There are 17,527 species, 296 subspecies, 2215 varieties, 33 subvarieties and 70 forma, altogether 20,141 taxa of angiosperms under 2991 genera and 251 families in India, representing approximately 7% of the described species in the world (Karthikeyan, 2009). However, the recent estimate accounts a total of 17926 species of angiosperms in the country (Singh & al., 2013). Family Poaceae is the largest in India being represented by 263 genera and 1291 species followed by Orchidaceae (184/1229), Leguminosae (173/1192), Asteraceae (167/950), Rubiaceae (113/616), Cyperaceae (38/545), Euphorbiaceae (84/528), Acanthaceae (92/510), Rosaceae (40/492) and Lamiaceae (72/454). A total of 42 families have more than 100 species each, while 33 families (including four monotypic families, viz. Circaesteraceae, Plagiopteraceae, Tetracentraceae and Trichopodaceae) are represented in India by only one species. According to Rana & Ranade (2009) a total of 236 monotypic genera (84 are endemics) are found in India, of which 176 are dicotyledones and remaining 60 are monocotyledones; Poaceae with 32 taxa are the most dominant family, followed by Leguminosae (15), Asteraceae (12), Rubiaceae (11) and Orchidaceae (10).

Impatiens with 205 taxa is the largest genus in Indian flora, followed by Primula (135), Ficus (132), Carex (117), Crotalaria (104), Dendrobium (100), Habenaria (100), Pedicularis (98), Rhododendron (97) and Syzygium (91). About half of the world’s aquatic angiosperms occur in India, and are chiefly distributed in families such as Alismataceae, Hydrocharitaceae, Najadaceae, Nymphaeaceae, Podostemaceae, Lemnaceae, Potamogetonaceae and Ceratophyllaceae, which alone collectively comprise a total of 107 aquatic species of angiosperms.

The angiospermic flora of India is further characterised by high endemism, which is next only to Australia. Nayar (1996) has identified 3 megacentres and 25 microcentres of endemic plants in Indian subcontinent based on the diversity and distribution of endemic species (Table 2).

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Table 2: Megacentres and Microcentres of Endemic Plants in Indian Subcontinent

According to Nayar (1996) about 5725 species of flowering plants are broadly considered as endemics and represent 33.5% of the flora, of which, 3471 species are found in the Himalayas, 2051 in the Peninsular India and 239 in Andaman & Nicobar Islands.  Besides 147 genera are endemic to India, out of these 71 genera are endemic to the Himalaya, 60 to Peninsular India and 1 genus, i.e., Pubistylus Thoth. is endemic to Andaman & Nicobar Islands, whereas 15 genera are widely distributed throughout the country. However, according to recent estimation about 4045 taxa belonging to 975 genera in 155 families are considered as strict endemics to the present Indian political boundary; dicotyledones dominate the endemic flora with 2984 taxa (74%) under 720 genera in 128 families whereas monocotyledones are represented by 1061 taxa (26%) belonging to 255 genera under 27 families (BSI in press).

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Indian flora is also rich in botanical curiosities, such as insectivorous plants [species of Aldrovanda (1); Drosera (3); Nepenthes (1); Pinguicula (1) and Utricularia (38)]; parasites (both root and stem), such as Balanophora spp., Boschniakia himalaica, Orobanche sp., Aeginetia indica, Rhopalocnemis phalloides, Sapria himalayana, Mitrastemon yamamotoi, Cuscuta reflexa, Viscum spp., Loranthus sp., Arceuthobium spp., and saprophytes such as Monotropa spp., Cymbidium macrorhizon and Galeola spp. The diversity in certain families, which are of immense ornamental value, is very interesting, for instance, the orchids, which are represented in India by over 1141 species with maximum representation in the Eastern Himalayas and the North-eastern region, have great horticultural potential because of their exquisite long-lasting flowers of various shapes, size and colour. Similarly, bamboos, which are closely associated with the social and cultural fabric of Indian masses, are also represented in India by 130 species out of 550 in the world, again with the maximum diversity in Northeast India.

The Northeast India, with the presence of over 130 species of primitive angiosperms is also considered as a “cradle of flowering plants” (Takhtajan, 1969). India is also recognised as one of the world's 12 Vavilovian centres of origin and diversification of cultivated plants, known as the "Hindustan Centre of origin of crop plants" (Vavilov, 1951). At least 167 species of important agri-horticultural crops and 320 species of their wild relatives, belonging to 116 genera and 48 families, are known to have originated here (Arora & Nayar, 1984). There are 50,000 to 60,000 land races of rice grown in India, and other economically important crops, such as wheat, sugarcane, legumes, sesame, eggplant, citrus, banana, mango, jute, ginger, turmeric, pepper, cinnamon and cardamom also have high level of diversity. It is estimated that about 3000 species of angiosperms are with potential medicinal values, of which ca. 1300 species are extensively used in different traditional systems of medicine such as Ayurveda, Siddha and Unani and also in Allopathy.

Gymnosperms: Gymnosperms are woody perennials, either shrubs or trees. There are 58 taxa growing in wild under 15 genera and 8 families in India (Singh & Mudgal, 1997). Though they are lesser in number, provide timber, wood, resins, tars and turpentine. Family Pinaceae is the largest represented by 6 genera and 17 species, followed by Cupressaceae (2/8); Ephedraceae (1/8); Gnetaceae (1/2); Cycadaceae (1/4). The genus Ephedra is the largest genus with 8 taxa followed by Pinus (7); Juniperus and Gnetum (5 each); Cycas (4). In addition, there are ca. 26 taxa under 12 genera which are introduced in various gardens, parks and as avenue trees across the country. Some of the popular exotics are Cycas revoluta, Ginkgo biloba, and species of Araucaria, Agathis and Pinus.

The conifers flora of India is dominated by the genera of Northern hemisphere, viz. Pinus, Abies, Cedrus and Picea. All Indian conifers except Podocarpus wallichianus (Peninsular India and Andamans) and Podocarpus neriifolius (Eastern Himalaya and Andamans) are restricted to Himalaya. The species of Cycas are distributed widely in Eastern and Western Ghats, Northeast India and Andaman & Nicobar Islands. Majority of the species of Ephedra are distributed in higher elevations of Himalaya preferably with alkaline soils. Similarly, the species of Gnetum inhabit evergreen tropical rain forests of Eastern and Western Ghats, Northeast India and Andaman & Nicobar Islands. Ephedra gerardiana and E. nebrodensis (good source of alkaloid ephedrine) and Taxus wallichiana (which yield anticancerous taxol) are highly valued and exploited medicinal plants.

Pteridophytes: Pteridophytes (fern and fem-allies) grow in a variety of habitats and in all climatic zones of the country showing maximum diversity between 1300 and 2400 m. About 1200 taxa under 204 genera are distributed in India (Ghosh & Ghosh, 1997). Though the pteridophytes prefer shady and moist places but a few, such as Adiantum lunulatum and Psilotum nudum grow on rocks covered with mosses and in rock crevices, and a few others, such as Woodsia elongata, Actiniopteris radiata survive in dry places.

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The Eastern Himalaya and the Northeast India with about 845 taxa in 179 genera, representing approximately 67% of the pteridopyhtes known from the country, followed by southern India, including Eastern and Western Ghats, with 345 taxa in 117 genera and Northern India, including Western Himalaya, with 340 taxa in 101 genera. About 17% of the total pteridophytic species are endemic to India. Certain species of Diplazium, Dryopteris and Marsilea are edible, whereas Adiantum capillus-veneris, Selaginella bryopteris and species of Lycopodium, Actiniopteris, Polystichum and Marsilea are well-known for their high medicinal properties.

Bryophytes: The less known group of plants, comprising about 2800 species, is the second largest group of green plants in India, next only to the angiosperms. They usually inhabit narrow ecological niches with preference for damp and shady conditions. The vast areas in the Himalayas and Peninsular India with abundant precipitation and high humidity are richer in bryophytes. The bryophytes in general are autotrophic, except genera Cryptothallus (a liverwort) and Buxbaumia (a moss). While the former does not occur in India, the latter is represented in our country by a single endemic species, B. himalayensis.

Mosses constitute the major component of Indian bryoflora with about 2000 species (including intraspecific categories) belonging to 342 genera and 54 families (Vohra & Aziz, 1997); of these, ca. 1030 occur in Eastern Himalaya, 751 in Western Himalaya and 540 in Western Ghats. About 16 genera and 678 species are endemic to India. Liverworts are represented by ca. 850 species under 140 genera and 52 families (Singh, 1997). The majority of them are damp loving, predominantly terrestrial and favour shaded conditions, whereas a number of taxa are epiphytic (species of Radula, Frullania, Plagiochila, Porella, Lejeunea), epiphyllous (species of Radula, Cololejeunea, Colura), aquatic (Riccia fluitans, Ricciocarpus natans and species of Riella) and xeromorphic (Reboulia hemisphaerica, Targionia hypophylla, Asterella angusta). About 260 taxa or ca. 30% of the total liverwort flora, including 1 family (Aitchisoniellaceae) and 5 genera (Aitchisoniella, Sewardiella, Stephensoniella, Sauchia and Diplocolea) are endemic to different regions of the country with maximum representation in Eastern Himalaya, (which account for ca. 60% of the total endemic taxa in the country) followed by Western Ghats and the Western Himalaya.

Lichens: Lichens are a symbiotic association of fungi and algae and constitute a dominant component of epiphytic and saxicolous vegetation. At present about 2021 species of lichens in 248 genera are known to occur in India (Singh & Sinha, 1997) constituting an interesting component of Indian flora across the tropical to alpine zones. Western Ghats are the richest with ca. 800 species (39 per cent) followed by Eastern Himalaya with 759 species (37 per cent) and Western Himalaya with 550 species (27%). Parmeliaceae, Graphidaceae, Physciaceae, Usneaceae Cladoniaceae and genera Pramelia, Graphina, Usnea, Graphis and Lecanora are among the dominant families and genera of Indian lichens. It has been estimated that ca. 466 or about 23% species, mainly belonging to genera such as Graphina, Trypethelium, Graphis and Porina are endemic to India. Andaman & Nicobar Islands (24%); Western Ghats (20%) and Eastern Himalaya (18%) show high percentage of endemic species. Apart from their use as bio-indicators of air pollution, the lichens in India are known for a variety of uses, such as spices and flavouring agents (species of Usnea, Ramalina, Parmotrema, Heterodermia); medicinal (species of Heterodermia, Peltigera, Stereocaulon) and edible (Evemiastrum cirrhatum). Over 30 species belonging to genera such as Usnea, Ramalina and Evemiastrum are used in perfume industry because of the presence of aromatic resinoids.

Fungi: Fungi range from microscopic organisms to huge solid bodies. Approximately 14,500 species in 2300 genera are found in India (Sharma, 1997) of which ca. 3500 species are endemic. Deuteromycotina (Fungi Imperfecti) together with Ascomycotina and Basidiomycotina account for more than 88 per cent of the Indian mycoflora. Deuteromycotina, alone represents ca. 40% followed by Ascomycotina (ca. 25%) and Basidiomycotina (ca. 23%). Cercospora belonging to Fungi Imperfecti group with ca. 707 species, is the largest fungal genus in India followed by Puccinia (320 spp.), Phyllosticta (ca. 280 spp.), Aspergillus (ca. 140 spp.), Meliola (ca. 130 spp.), Phyllachora (ca. 116 spp.) and Aecidium (ca. 100 spp.). The number of recorded species from India could be an underestimate in view of the fact that major part of the country has not yet been explored mycologically. India also harbours a varied wealth of edible mushrooms.

Algae: Represented by over 6500 species in ca. 666 genera, they are found growing in a variety of habitats ranging from fresh water, marine, terrestrial and to soil. Of which 1924 species are endemic to the country. According to Rao & Gupta (1997) fresh water algae are dominated by Chlorophyceae (green algae), Bacillariophyceae (diatoms) and Cyanophyceae (blue green algae) represent the major portion of Indian algal flora accounting for ca. 390 genera and 4500 species  followed by terrestrial algae (125 genera and 615 spp.); soil algae (80 genera and 1500 spp.); marine algae (169 genera and 680 spp.).

Out of ca. 680 marine algal species so far described from Indian coasts (Rao & Mudgal, 1997), ca. 50% belong to Rhodophyceae (Red algae), 25% to Chlorophyceae (Green algae), 22% to Phaeophyceae (Brown algae) and 3% to Cyanophyceae (Blue green algae). The Gujarat coast, the islands in Gulf of Mannar and Andaman & Nicobar group of islands are of special interest in view of luxuriance and variety of marine algae. In India, over 45 species of marine algae are useful mainly as source of Agar-Agar (species of Gelidium, Gelidiella and Gracilaria) and Algins (species of Sargassum, Turbinaria, Dictyota and Padina). Some species are also useful as food (species of Ulva. Enteromorpha, Turbinaria, Gracilaria and Porphyra); as fodder (species of Dictyota, Padina and Sargassum) and manure (all sea weeds in coastal areas).

Status and Conservation

Over 30% of the geographical area of our country, including that in the Himalayas, the Western Ghats and the Andaman and Nicobar Islands, still remain to be floristically explored and inventorised. Besides, despite the country being bestowed with vast natural as well as man-made wetlands distributed across different altitudinal and climatic zones, our knowledge about the floristic diversity met in these most fragile ecosystems is far from complete.

The biodiversity of our country is under considerable degree of threat due to various factors, both natural and man-made. Natural causes, such as natural calamities, competition between species and biological impairity of a species, have contributed, to some extent, towards the depletion of certain species, e.g. Eremostachys superba, Frerea indica (Angiosperms); Aitchisoniella himalayensis, Monoselenium     tenerum, Sewardiella tuberifera, Stephensoniella brevipedunculata (Bryophytes), it is the man-made threats, such as clearance of prime forests for agriculture, mining, urbanisation, industrialisation, grazing, over-exploitation of components of floristic diversity and introduction of alien species which have severely threatened many of the wild species. It is estimated that 26,106 plant species are globally threatened.

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