Plant Diversity and Angiosperms in India

Plant Diversity and Angiosperms in India INTRODUCTION Angiosperms or flowering plants (also called Angiospermae, Magnoliophyta, or Anthophyta) are the most diverse group of the plant kingdom, comprising of about 2,50,000 species in 350 families (Kenrick, 1999). Flowering plants are by far the most numerous, diverse, and â€Å"successful† extant plant group, containing well over 95% of all land plant species alive today (Simpson, 2006). Angiosperms are characterized by (i) seeds produced within a carpel with a stigmatic surface for pollen germination, (ii) a much reduced female gametophyte, consisting in most cases of just eight nuclei in seven cells; and (3) double fertilization, leading to the formation of a typically triploid nutritive tissue called endosperm (Judd et al., 2002). Several apomorphies distinguish the angiosperms from all other land plants: (1) the flower, usually with an associated perianth, (2) stamens with two lateral thecae, each composed of two microsporangia, (3) a reduced, 3-nucleate male gametophyte, (4) c arpels and fruit formation, (5) ovules with two integuments, (6) a reduced, 8-nucleate female gametophyte, (7) endosperm formation and (8) sieve tube members (Simpson, 2006). Some of these apomorphic features, which represent the product of a unique evolutionary event, have become further modified in particular lineages of angiosperms. Almost all angiosperms produce vessels in the xylem tissue, though this feature probably evolved within the group. Angiosperm phloem differs from that of all other plants in having sieve tube elements accompanied by one or more â€Å"companion cells† that are derived from the same mother cell. Flowering plants grow in virtually every habitable region and are dominant in some aquatic and most terrestrial ecosystems, the notable exception to the latter being coniferous forests. Angiosperms comprise the great bulk of our economically important plants, including our most valuable food crops. India with a geographical area of about 32, 87,263 sq km is the seventh largest and tenth industrialized country of the world. It is situated between 804 N to 3706 N latitude and 6807 E to 97025 E longitude. The longitudinal variation divides Indian subcontinent into four climatological zones, viz., equatorial, tropical, subtropical and warm temperate. The forest cover of the country have been estimated to be 6, 37,293 km2 (19.39% of the geographic area of the country) and includes dense forest (3, 77,358 km2), open forest (2, 55,064 km2) and mangrove (4,871 km2). India represents about 11% of world’s flora in just about 2.4% of total land mass. Out of the 25 biodiversity ‘Hotspots’ identified in the world (Myers, 1990), India has two, namely Eastern Himalaya and Western Ghats. These hotspots posses majority of plant diversity in India. In terms of species diversity, approximately 45,000 plant species are found in India (Khoshoo, 1994, 1995; Sharma et al., 1997). The angiosperms are represented by c. 17,500 species out of which 5725 species are endemic to India. About 28% of the total Indian flora and about 33% of angiosperms occurring in India are endemic (Nayar, 1996). It is roughly estimated that about 10% of flowering plant species in India are threatened and 34 plant species have been reported to be extinct (Nayar and Sastry, 1987-1990). The studies on Indian plants were first initiated by the European visitors. Even before the publication of Species Plantarum by Linnaeus (1753), Hendrik Van Rheede (1678-1703) started publication of his monumental 12 volume work ‘Hortus Malabaricus’. However, actual work on Indian flora was initiated by Roxburgh (1814, 1820- 1824) and later by Hooker and Thompson (1855). The publication of Flora of British India by Sir J.D. Hooker (1872- 1897) gave a stimulus to taxonomic studies in our country and since then several regional and state floras have been published. In 1954, Botanical Survey of India was revived with a view to make intensive studies of local flora especially to gather precise information on the identity, floristic diversity, distribution, ecological association, phenology, medicinal and economic uses of plants. India is immensely rich in biological diversity. Such richness is largely due to varied physical environment, latitude, altitude, geology and climate. The climate and altitudinal variations coupled with varied ecological habitats have contributed in the development of immensely rich vegetation wealth, and varied flora and fauna forming a very unique biodiversity. Seeing the rich plant diversity, Hooker (1904) commented that ‘The Indian flora is more varied than that of any other country of equal area in the eastern hemisphere, if not on the globe’. The Indian flora represents taxa occurring in different countries including Afghanistan, Bhutan, Bangladesh, China, Nepal, Pakistan, Myanmar, Malaysia, Indonesia, Thailand and Indo-China. There are even the representatives from African, American, Australian and European countries. DISTRIBUTION AND HABITAT Bio-geographical Territories in World The Indian region is one of the most diverse bio-geographic regions of the world having wide ranging topography from permanently snow covered high Himalayan ranges to plains at sea level, low lying swamps and mangroves, island systems, tropical evergreen rain forests, fertile alluvial plains, hot deserts and high altitude cold deserts. The climate ranges from tropical and sub-tropical in Indo-Gangetic plains and in the peninsular regions to temperate and arctic in the Himalayan region. Biogeographically India represents two of the major realms (Palaearctic and Indo-Malayan) and three biomes. Considering the vastness of the country and variation pattern in different areas, the country is divided into ten botanical regions with distinct bioclimatic conditions. These include: Coromandal coast, Malabar, Indus plain, Indian desert, Gangetic plain, Assam, Eastern Himalaya, Central Himalaya, Western Himalaya, Andaman and Nicobar Islands and Lakshdweep and minicoy group of islands (Mudgal and Hajra, 1997). India harbors very diverse climatic conditions and thus fosters different types of habitats. The major mountain ranges in India are the Himalaya and the Western Ghats. The Indian Himalayan region is spread over the states of Jammu and Kashmir, Himachal Pradesh, Sikkim, Arunachal Pradesh, Nagaland, Manipur, Mizoram, Tripura, Meghalaya, and a part of Assam, along with eight districts of Uttarakhand and one district of West Bengal. Biogeographically, the Indian Himalayan region falls under Boreal Zone which has two sub-zones, viz., Sino-Siberian and Sino-Himalayan. The area can be divided into four distinct zones longitudinally: (i) the Siwalik (900 – 1500 m), (ii) the outer Himalaya (1500 – 3500 m), (iii) the middle or lesser Himalaya (3600 – 4600 m), and (iv) the Greater Himalaya (above 4,600 m). This complex mountain system consists of narrow and deep valleys, glaciers and fertile terrain. Five climatic zones can be delineated in the Himalayan region based on geographic and physiographic factors. These are: (1) Warm tropical, (2) Warm sub-tropical, (3) Cool temperate, (4) Alpine and (5) Arctic. While these are only broad zonations, there are many local variations in the climate due to precipitation, temperature, wind patterns, humidity etc. The type and nature of soils also vary vastly in the Himalayan region from deep alluvial to the thin and bare soils of the high mountains. The nature of the soil depends upon the rocks, the prevailing climatic conditions, topography and vegetation. According to Udvardy (1975), biodiversity exists on earth in 8 broad realms with 193 bio-geographical provinces. It has been estimated that world’s 12 countries Australia, Brazil, China, Columbia, Ecuador, India, Indonesia, Madagascar, Malaysia, Mexico, Peru and Zaire together hold 70% of its total flowering plant diversity. These countries have been termed as â€Å"Megadiversity† countries (Mc Neely et al., 1990) Rodgers and Panwar (1990) have divided India into 10 phytogeographic zones and 24 biotic provinces. Gadgil and Meher-Homji (1990) have recognized 16 phytogeographical zones in India. On the other hand, Das (1996) has recognized 9 physiographic regions within the Indian Territory. Chowdhery and Murti (2000) have recognized 11 phytogeographic regions for India, each of which have its uniqueness in ecosystem, vegetation and floristic composition. These phytogeographic regions are: Western Himalaya, Eastern Himalaya, Gangetic plains, North East India, Semi arid and Arid regions, Deccan Plateau, Western Ghats, Eastern Ghats, Andaman and Nicobar Islands, Lakshdweep and Coastal regions. Distribution of Angiosperms in India In India, the vascular plants form the most dominant and conspicuous vegetation cover comprising of over 17,500 species of angiosperms which represents more than 7% of the worlds known flowering plant species (Hooker, 1872-1897; Karthikeyan et al., 1989; Sharma and Balakrishnan, 1993; Sharma and Sanjappa, 1993; Sharma et al., 1993; Hajra et al., 1995; Mudgal and Hajra 1997- 1999; Singh et al., 2000; Karthikeyan, 2000). These species are distributed in more than 4000 genera occurring in diffenent ecosystems from the humid tropics of Western Ghats to the Alpine zones of the Himalayas and from Mangrooves of tidal Sunderbans to the dry desert of Rajasthan. In India, dicots are represented by 2,282 genera and 12,750 species whereas monocots are represented by 702 genera and 4,250 species. Dicots account for c. 75% of flowering plants in terms of both genera and species. On the other hand, remaining 25% is contributed by monocots. Out of 511 recognized plant families (Brummit, 1992), 320 families with more than 4000 genera are represented in the Indian flora. Of which Poaceae is the largest family with about 263 genera and more than 1200 species. In India, over 60 families of flowering plants are monotypic, e.g., Illiciaceae, Ruppiaceae, Turneraceae, Tetracentraceae, etc. Asragaluts, Carex, Dendrobium, Ficus, Habenaria, Impatiens, Primula, Rhododendron, Saussurea, Taraxacum, etc. are some of the dominant genera of flowering plants in India. Out of the estimated 17,500 species of angiosperms, approximately 15% species are trees which include some of the highly valued timber species of the world and belong to the families like Annonaceae, Dipterocarpaceae, Euphorbiaceae, Fabaceae, Lauraceae, Moraceae, Meliaceae, Verbenaceae, etc. There are several botanical curiosities like Aeginetia indica, Balanophora dioica, Boschiniackia himalaica, Drosera, Epipogium, Galeola, Mitrastemon yamamotoi, Monotropa, Nepenthes khasiana, Pinguicula, Sapria himalayana, Utricularia spp., etc. Species in certain groups like Orchids, Bamboos, Rhododendrons, Citrus, Hedychiums, Impatiens, Pedicularis, Primulas, etc. exhibit remarkable diversity in India (Rao, 1994). Dominant angiospermic families in India are given in table1 (after Groombridge, 1992; Sharma et al., 1997). Table 1. Dominant families of dicots and monocots Insectivorous and parasitic plants The carnivorous plants (insectivorous plants) trap and digest insects to meet the requirement of nitrogen deficiency. Altogether over 450 species of carnivorous plants have been reported of which approximately 30 species occur in India. The insectivorous taxa belong to family Droseraceae (3 spp.), Nepenthaceae (1 spcies) and Lentibulariaceae (36 spp.). The parasitic plant species are prominent in Loranthaceae (46 spp.), Santalaceae (10 spp.), Balanophoraceae (6 spp.), Rafflesiaceae (1 spp.), Cuscutaceae (12 spp.) and Orobanchaceae (54 spp.). Aquatic plants About 2 percent of all flowering plants known in the world inhabit water bodies and more than 50 percent of these are represented in Indian subcontinent (Lavania et al., 1990). Some important aquatic plants families are: Alismataceae (8 spp.), Aponogetonaceae (6 spp.), Azollaceae (1 sp.), Barclayaceae (2 spp.), Butomaceae (1 sp.), Cabombaceae (2 spp.), Callitrichaceae (3 species), Isoetaceae (10 spp.), Lemnaceae (14 spp.), Najadaceae (7 spp.), Nelumbonaceae (1 sp.), Nymphaeaceae (7 spp.), Podostemaceae (24 spp.), Pontederiaceae (13 spp.), Ceratophyllaceae (3 spp.), Hydrocharitaceae (13 spp.), Potamogetonaceae (18 spp.), Ruppiaceae (1 sp.), Salviniaceae (3 spp.), Trapaceae (2 spp.), Typhaceae (4 spp.), Zannichelliaceae (1 sp.), etc. The members of families Podostemaceae and Tristichaceae grow on rocks under water in fast flowing streams. The aquatic plants in India are highly diversified comprising free-floating forms (Eichhornia crassipes, Lemna perpusila, Nymphoides hydrophylla, Trapa natans var. bispinosa, Pistia stratiotes, Wolffia microscopia, W. globosa), rooted aquatics with their foliage floating (Nymphaea nouchali, N. stellata, Euryale ferox, Nelumbo nucifera), submerged aquatics (Vallisnaria natans, Hydrilla verticillata, Najas graminea, Potamogeton pectinatus) emergent aquatics (Scirpus maritimus, Cyperus articulates, Sagittaria trifolia, S. guayanensis subsp. leppula) and marsh plants (Ranunculus scleratus, Hydrolea zeylanica, Panicum paludosum, Polygonum barbatum, P. glabrum). The aquatic flora play an important role as water purifier by absorbing heavy metals, e.g. Ceratophyllum demersum (chromium), Bacopa monnieri (copper and cadmium). Limosella aquatica, Hippuris vulgaris occur in subalpine-alpine lakes. Mangroves Mangroves are the plants that inhabit coastal regions and estuaries. They are adapted to survive under marshy conditions. In India, mangroves cover an area of approximately 6700 Km ² which constitutes c. 7 percent of the world’s mangroves. The largest stretch of mangroves in India occurs in Sunderbans (West Bengal) which covers an area of about 4200 km ². It has been designated as World Heritage site of which 80% of them are restricted to Sunderbans (West Bengal) and Andaman Nicobar islands (Chowdhery and Murti, 2000). The remaining taxa are scattered in the coastal areas of Andhra Pradesh, Tamil Nadu, Orissa, Maharashtra, Gujarat, Goa and Karnataka. Some of the dominant mangrove species include Avicennia marina, A. officinalis, Bruguiera gymnorrhiza, B. parviflora, Ceriops tagal, Heritiera fomes, Lumnitzera spp., Rhizophora mucronata, R. apiculata, R. stylosa, Sonneratia spp., Xylocarpus spp., etc. The shrubby Aegialitis rotundifolia and Acanthus ilicifolius are common o n poor saline plains. The herbaceous succulent halophytes are represented by Aegiceras corniculatus, Suaeda brachiata, Sesuvium portulacastrum and Salicornia brachiata. The characteristic mangrove palms are: Nypa fruticans and Phoenix paludosa. Indicator species Some species of angiosperms growing on metalliferous soils accumulate large amounts of metals in their roots and reflect the levels of metal present in the soil (indicators). For example, presence of copper is indicated by Astragalus spp., Croton roxburghii, Hyptis suaveolens, Holarrhena pubescens, Impatiens balsamina, Vernonia cinerea, and indicates presence of Uranium (Aery, 1977; Venkatesh, 1964, 1966). Diversification of Primitive and Advanced Families The primitive families are confined to those regions which are very old in geological time scale in comparison to the newly developed areas. Assam, North-east Indian region and Deccan Peninsula are older in comparison to the other phytogeographical regions of India. These regions are more or less identical in age with Sri Lanka, South West Chinese region and Malay Peninsula. The Deccan Peninsula shows its floristic relationship with Sri Lanka and Malay provinces, while the North east India shows its floristic relationship with Myanmar, South West Chinese Provinces and Malay Peninsula. Thus the Malay region shows similarity with Deccan Peninsula on one hand and North east India on the other. By this way the North East India shows similarity with Deccan Peninsula to some extent (Mitra and Mukherjee, 2006). India (Eastern Himalaya including North east India) is considered as a sanctuary of primitive flowering plants. The occurrence of such a large number of primitive angiosperms led Takhtajan (1969) to designate this region as the ‘Cradle of Flowering Plants’ where angiosperms have diversified (Table 2) Table.2. Primitive flowering plants occurring in India (after Rao, 1994) The advanced families occur in those areas which are comparatively very young in the geological time scale. On the basis of this idea it can be stated that the Himalayan region of India is very young in its age as compared to Deccan Peninsula and North East Indian regions of India, as it harbours most of the advanced families with well diversified restricted genera and species. A comparative account of diversification of primitive and advanced families of India and its adjoining area is given in table 3. The advanced families are young in their age and also they are confined to the areas which are also geologically young, they are unable to spread in the wider regions. On the other hand, primitive plant families are older in their age and also found to confined in those areas which are geologically very old. So they get sufficient time to spread over larger areas, as a result of which the primitive families show less number of restricted genera and species in their credit in comparison to the advanced families (Mitra and Mukherjee, 2006). Habitats Different ecological habitats occur in India ranging from tropical rainforest, subtropical savanna or shrublands, temperate forest, alpine mosses to xerophytic variation of desert. The habitat types vary from the humid tropical Western Ghats to the hot deserts of Rajasthan, from cold deserts of Ladakh to the long, warm cost line stretches of peninsular India. While Cherrapunji and Mawphlong in the north-eastern state of Meghalaya are the two wettest places on earth, Dras in Ladakh is the coldest inhabited place of the world. Phytogeographically, the eastern Himalaya forms a distinct floristic region. The area comprises Nepal, Bhutan, and neighboring states of northern India along a continuous sector of the Yunnan province in south-west China. In Nepal, there are around 7000 plant species, many of which overlap those of India, Bhutan and even Yunnan. Of these species, at least 500 (almost 8%) are believed to be endemic to Nepal. Bhutan possesses an estimated 5000 species, of which as many as 750 (15%) are considered to be endemic to the eastern Himalaya (Anonymous 1999). This region is the meeting ground of the Indo-Malayan, Afro-tropic and Indo-Chinese biogeographical realms as well as the Himalayan and Peninsular Indian elements, formed when the peninsular plate struck against the Asian landmass, after it broke off from Gondwana land. The region is recognized as refugium of flowering plants and center of active speciation (Rao, 1994). The numerous primitive angiosperm families found in this region inclu de Degeneriaceae, Eupomatiaceae, Himantandraceae, Lardizalbalaceae, Magnoliaceae, Trochodendraceae, Tetracentraceae, Winteraceae. The primitive genera are Alnus, Aspidocarya, Betula, Decaisnea, Euptelea, Exbucklandia, Haematocarpus, Holboellia, Houttuynia, Magnolia, Mangelietia, Pycnarrhena, and Tetracentrol (Malhotra and Hajra 1977). Regions of High Diversity India is one of the 12 mega biodiversity countries of the world. It represents an example of conglomeration of diverse bioclimates influenced by neighbouring areas (particularly Mediterranean), the unique location, peninsular land mass, Gangetic plains and the crown of complex chain of mountain systems – the Himalaya. The Himalayan region with only 18% of India’s land area, houses 81.4% of the country’s stock of gymnosperms, 47% of angiosperms, 59.5% of lichens, 58.7% of pteridophytes, 43.9% of bryophytes and 53.07% of fungi found in India. Orchidaceae with over 1331 taxa (S. Misra, 2007) is one of the dominant families and probably the second largest among all families of flowering plant known from India. Of these 407 taxa are endemic to India. Out of the 18 monotypic orchid genera of India, 13 are found in the Himalayan region. In the Eastern Himalaya, the Orchid family is the largest, with 60% species, whereas in the Western Himalaya, Asteraceae with 540 species is the largest family followed by Poaceae with 439 species and Fabaceae with 362 species. Carex with more than 100 species and infraspecific categories is the largest genus in the Himalaya. Rhododendron with 96 species and infra-specific categories, and Astragalus with 90 species, is the largest genera in the Eastern and Western Himalaya, respectively. Some other plants with pronounced diversity in the Eastern Himalaya include the Hedychium (Zingiberaceae) with 18 species out of 35 Indian species, and numerous species of bamboos. The Eastern Himalaya is a cradle of numerous primitive angiosperms, such as Manglietia and Euptelea (Magnoliaceae) and Tetracentron (Tetracentraceae). Christollea himalayensis, recorded from Mt. Camet is the flowering plant occurring at the highest altitude (6300 msl). Arceuthobium minutissimum, (small angiosperm) grows on Himalayan conifers. Apart from these botanical curios, the Himalayan region has a rich diversity of medicinal and aromatic plants. The floristic richness has also rendered the North-Eastern region and Western Ghats to be recognized as two hotspots among 25 hotspots identified throughout the world. The humid tropical conditions met within these regions not only support exceptionally diverse vegetation but have also resulted in speciation in several genera, thus adding to the high endemicity of the flora (Nayar, 1996). In addition to these two, there are about 40 other sites in different phytogeographical zones of India which have high degree of endemism and genetic diversity. Mc Neely et al. (1990) estimated that 70% of worlds total flowering plants occur in 12 countries and these have been designated as Mega diversity centres or mega ­biodiversity country. The earth’s 25 biodiversity hotspot regions collectively cover about 2% of the planet’s land surface, yet claim more than 50% of all terrestrial species diversity. They have within them a phenomenal 1, 25,635 plant species. The top 11 hotspots (out of 25) for plant endemism harbor 5000 or more species as endemics. It accounts for 93,214 plant species, or 37.3% of the total global plant endemics (Myers 1988). Western Ghats The Western Ghats, which covers an area of approximately 1, 60,000 Km ², are among the 25 biodiversity hotspots globally identified. The wide variation of rainfall patterns in the Western Ghats, coupled with the regions complex geography, produces a great variety of vegetation types. These include scrub forests in the low-lying rain shadow areas and the plains, deciduous and tropical rainforests up to about 1,500 meters, and a unique mosaic of montane forests and rolling grasslands above 1,500 meters. Based on the ecological factors and floristic composition, four major forests and 23 floristic types have been identified. Eastern Himalaya Eastern Himalaya covering the states of Sikkim, Darjeeling district of West Bengal, Assam, Manipur, Tripura, Meghalaya, Arunachal Pradesh, Mizoram and Nagaland is the richest of the phytogeographic regions of India affording the highest plant/ animal diversity (Rao, 1994). This region is characterized by high rainfall and humidity. The abundant rains and high humidity contribute the occurrence of largest number of species in this region. North eastern region of India, blessed with wide range of physiography and ecoclimatic conditions, is the richest biodiversity centres of the Indian subcontinent (Hooker and Thompson, 1855; Hooker, 1905; Chatterjee, 1962; Rao, 1974). The north eastern India has a geographical area of about 2, 55,050 Km ². The rich plant wealth of this region has been reported by Hooker (1854). Further, Hooker’s work on â€Å"Flora of British India† (1872-97) and â€Å"Sketches on Flora of British India† (1905), presents a very detailed account on vegetation and flora of this region. Kanjilal et al. (1934-1940), in their â€Å"Flora of Assam† have provided a detailed account with emphasis on woody flora of this region. There are works on â€Å"Forest flora of Meghalaya† by Haridasan and Rao (1985, 1987) and â€Å"Grasses of North eastern India† by Shukla (1996). There are several genera endemic to Eastern Himalaya. Some important endemic genera are Aucuba, Bryocarpum, Pleurospermopsis, Gamblea, Lepidostemon, Parajaeschkaea, Paroxygraphis, Risleya, Sphaerosacme, Treutlera and Brachycaulos. Cyathopus is endemic to Sikkim. Some genera like Biswarea, Hymenandra, Jejosephia, Neoluffa, Pauia, etc. are endemic to North eastern India. Some important Eastern Himalayan endemic species are Abies densa, Agapetes incurvata, A. sikkimensis, Dipsacus atratus, Eriobotrya hookeriana, Geum macrosepalum, Larix griffithiana, Lindera heterophylla, Liparis perpusilla, Lloydia flavonutans, Maddenia himalica, Meconopsis grandis, M. superba, M. villosa, Myricaria albiflora, Primula whitei, Rhododendron baileyi, R. camelliaeflorum, R. ciliatum, R. glaucophyllum, R. grande, R. lantanum, R. lindleyi, R. wallichii, R .wightii, Rubus fragarioides, Sassurea conica, Acanthus leucostachys, Aconitum assamicum, Anoectochilus sikkimensis, Aeschynanthus parasiticus, Baliospermum micranthum, Berberis dasyclada, Calamus leptospadix, Calanthe densiflora, Capparis acutifolia, Cotoneaster assamensis, etc. (Chowdhery and Murti, 2000) Plant Diversity in Western Himalaya The Western Himalayan region is one of the 12 biogeographic regions of India and includes Jammu and Kashmir, Himachal Pradesh, and Uttaranchal. This region constitutes the alpine zone, temperate, humid and warm climatic conditions. The main portion of Western Himalaya lies in J K state comprising 67.5 Plant Diversity and Angiosperms in India Plant Diversity and Angiosperms in India INTRODUCTION Angiosperms or flowering plants (also called Angiospermae, Magnoliophyta, or Anthophyta) are the most diverse group of the plant kingdom, comprising of about 2,50,000 species in 350 families (Kenrick, 1999). Flowering plants are by far the most numerous, diverse, and â€Å"successful† extant plant group, containing well over 95% of all land plant species alive today (Simpson, 2006). Angiosperms are characterized by (i) seeds produced within a carpel with a stigmatic surface for pollen germination, (ii) a much reduced female gametophyte, consisting in most cases of just eight nuclei in seven cells; and (3) double fertilization, leading to the formation of a typically triploid nutritive tissue called endosperm (Judd et al., 2002). Several apomorphies distinguish the angiosperms from all other land plants: (1) the flower, usually with an associated perianth, (2) stamens with two lateral thecae, each composed of two microsporangia, (3) a reduced, 3-nucleate male gametophyte, (4) c arpels and fruit formation, (5) ovules with two integuments, (6) a reduced, 8-nucleate female gametophyte, (7) endosperm formation and (8) sieve tube members (Simpson, 2006). Some of these apomorphic features, which represent the product of a unique evolutionary event, have become further modified in particular lineages of angiosperms. Almost all angiosperms produce vessels in the xylem tissue, though this feature probably evolved within the group. Angiosperm phloem differs from that of all other plants in having sieve tube elements accompanied by one or more â€Å"companion cells† that are derived from the same mother cell. Flowering plants grow in virtually every habitable region and are dominant in some aquatic and most terrestrial ecosystems, the notable exception to the latter being coniferous forests. Angiosperms comprise the great bulk of our economically important plants, including our most valuable food crops. India with a geographical area of about 32, 87,263 sq km is the seventh largest and tenth industrialized country of the world. It is situated between 804 N to 3706 N latitude and 6807 E to 97025 E longitude. The longitudinal variation divides Indian subcontinent into four climatological zones, viz., equatorial, tropical, subtropical and warm temperate. The forest cover of the country have been estimated to be 6, 37,293 km2 (19.39% of the geographic area of the country) and includes dense forest (3, 77,358 km2), open forest (2, 55,064 km2) and mangrove (4,871 km2). India represents about 11% of world’s flora in just about 2.4% of total land mass. Out of the 25 biodiversity ‘Hotspots’ identified in the world (Myers, 1990), India has two, namely Eastern Himalaya and Western Ghats. These hotspots posses majority of plant diversity in India. In terms of species diversity, approximately 45,000 plant species are found in India (Khoshoo, 1994, 1995; Sharma et al., 1997). The angiosperms are represented by c. 17,500 species out of which 5725 species are endemic to India. About 28% of the total Indian flora and about 33% of angiosperms occurring in India are endemic (Nayar, 1996). It is roughly estimated that about 10% of flowering plant species in India are threatened and 34 plant species have been reported to be extinct (Nayar and Sastry, 1987-1990). The studies on Indian plants were first initiated by the European visitors. Even before the publication of Species Plantarum by Linnaeus (1753), Hendrik Van Rheede (1678-1703) started publication of his monumental 12 volume work ‘Hortus Malabaricus’. However, actual work on Indian flora was initiated by Roxburgh (1814, 1820- 1824) and later by Hooker and Thompson (1855). The publication of Flora of British India by Sir J.D. Hooker (1872- 1897) gave a stimulus to taxonomic studies in our country and since then several regional and state floras have been published. In 1954, Botanical Survey of India was revived with a view to make intensive studies of local flora especially to gather precise information on the identity, floristic diversity, distribution, ecological association, phenology, medicinal and economic uses of plants. India is immensely rich in biological diversity. Such richness is largely due to varied physical environment, latitude, altitude, geology and climate. The climate and altitudinal variations coupled with varied ecological habitats have contributed in the development of immensely rich vegetation wealth, and varied flora and fauna forming a very unique biodiversity. Seeing the rich plant diversity, Hooker (1904) commented that ‘The Indian flora is more varied than that of any other country of equal area in the eastern hemisphere, if not on the globe’. The Indian flora represents taxa occurring in different countries including Afghanistan, Bhutan, Bangladesh, China, Nepal, Pakistan, Myanmar, Malaysia, Indonesia, Thailand and Indo-China. There are even the representatives from African, American, Australian and European countries. DISTRIBUTION AND HABITAT Bio-geographical Territories in World The Indian region is one of the most diverse bio-geographic regions of the world having wide ranging topography from permanently snow covered high Himalayan ranges to plains at sea level, low lying swamps and mangroves, island systems, tropical evergreen rain forests, fertile alluvial plains, hot deserts and high altitude cold deserts. The climate ranges from tropical and sub-tropical in Indo-Gangetic plains and in the peninsular regions to temperate and arctic in the Himalayan region. Biogeographically India represents two of the major realms (Palaearctic and Indo-Malayan) and three biomes. Considering the vastness of the country and variation pattern in different areas, the country is divided into ten botanical regions with distinct bioclimatic conditions. These include: Coromandal coast, Malabar, Indus plain, Indian desert, Gangetic plain, Assam, Eastern Himalaya, Central Himalaya, Western Himalaya, Andaman and Nicobar Islands and Lakshdweep and minicoy group of islands (Mudgal and Hajra, 1997). India harbors very diverse climatic conditions and thus fosters different types of habitats. The major mountain ranges in India are the Himalaya and the Western Ghats. The Indian Himalayan region is spread over the states of Jammu and Kashmir, Himachal Pradesh, Sikkim, Arunachal Pradesh, Nagaland, Manipur, Mizoram, Tripura, Meghalaya, and a part of Assam, along with eight districts of Uttarakhand and one district of West Bengal. Biogeographically, the Indian Himalayan region falls under Boreal Zone which has two sub-zones, viz., Sino-Siberian and Sino-Himalayan. The area can be divided into four distinct zones longitudinally: (i) the Siwalik (900 – 1500 m), (ii) the outer Himalaya (1500 – 3500 m), (iii) the middle or lesser Himalaya (3600 – 4600 m), and (iv) the Greater Himalaya (above 4,600 m). This complex mountain system consists of narrow and deep valleys, glaciers and fertile terrain. Five climatic zones can be delineated in the Himalayan region based on geographic and physiographic factors. These are: (1) Warm tropical, (2) Warm sub-tropical, (3) Cool temperate, (4) Alpine and (5) Arctic. While these are only broad zonations, there are many local variations in the climate due to precipitation, temperature, wind patterns, humidity etc. The type and nature of soils also vary vastly in the Himalayan region from deep alluvial to the thin and bare soils of the high mountains. The nature of the soil depends upon the rocks, the prevailing climatic conditions, topography and vegetation. According to Udvardy (1975), biodiversity exists on earth in 8 broad realms with 193 bio-geographical provinces. It has been estimated that world’s 12 countries Australia, Brazil, China, Columbia, Ecuador, India, Indonesia, Madagascar, Malaysia, Mexico, Peru and Zaire together hold 70% of its total flowering plant diversity. These countries have been termed as â€Å"Megadiversity† countries (Mc Neely et al., 1990) Rodgers and Panwar (1990) have divided India into 10 phytogeographic zones and 24 biotic provinces. Gadgil and Meher-Homji (1990) have recognized 16 phytogeographical zones in India. On the other hand, Das (1996) has recognized 9 physiographic regions within the Indian Territory. Chowdhery and Murti (2000) have recognized 11 phytogeographic regions for India, each of which have its uniqueness in ecosystem, vegetation and floristic composition. These phytogeographic regions are: Western Himalaya, Eastern Himalaya, Gangetic plains, North East India, Semi arid and Arid regions, Deccan Plateau, Western Ghats, Eastern Ghats, Andaman and Nicobar Islands, Lakshdweep and Coastal regions. Distribution of Angiosperms in India In India, the vascular plants form the most dominant and conspicuous vegetation cover comprising of over 17,500 species of angiosperms which represents more than 7% of the worlds known flowering plant species (Hooker, 1872-1897; Karthikeyan et al., 1989; Sharma and Balakrishnan, 1993; Sharma and Sanjappa, 1993; Sharma et al., 1993; Hajra et al., 1995; Mudgal and Hajra 1997- 1999; Singh et al., 2000; Karthikeyan, 2000). These species are distributed in more than 4000 genera occurring in diffenent ecosystems from the humid tropics of Western Ghats to the Alpine zones of the Himalayas and from Mangrooves of tidal Sunderbans to the dry desert of Rajasthan. In India, dicots are represented by 2,282 genera and 12,750 species whereas monocots are represented by 702 genera and 4,250 species. Dicots account for c. 75% of flowering plants in terms of both genera and species. On the other hand, remaining 25% is contributed by monocots. Out of 511 recognized plant families (Brummit, 1992), 320 families with more than 4000 genera are represented in the Indian flora. Of which Poaceae is the largest family with about 263 genera and more than 1200 species. In India, over 60 families of flowering plants are monotypic, e.g., Illiciaceae, Ruppiaceae, Turneraceae, Tetracentraceae, etc. Asragaluts, Carex, Dendrobium, Ficus, Habenaria, Impatiens, Primula, Rhododendron, Saussurea, Taraxacum, etc. are some of the dominant genera of flowering plants in India. Out of the estimated 17,500 species of angiosperms, approximately 15% species are trees which include some of the highly valued timber species of the world and belong to the families like Annonaceae, Dipterocarpaceae, Euphorbiaceae, Fabaceae, Lauraceae, Moraceae, Meliaceae, Verbenaceae, etc. There are several botanical curiosities like Aeginetia indica, Balanophora dioica, Boschiniackia himalaica, Drosera, Epipogium, Galeola, Mitrastemon yamamotoi, Monotropa, Nepenthes khasiana, Pinguicula, Sapria himalayana, Utricularia spp., etc. Species in certain groups like Orchids, Bamboos, Rhododendrons, Citrus, Hedychiums, Impatiens, Pedicularis, Primulas, etc. exhibit remarkable diversity in India (Rao, 1994). Dominant angiospermic families in India are given in table1 (after Groombridge, 1992; Sharma et al., 1997). Table 1. Dominant families of dicots and monocots Insectivorous and parasitic plants The carnivorous plants (insectivorous plants) trap and digest insects to meet the requirement of nitrogen deficiency. Altogether over 450 species of carnivorous plants have been reported of which approximately 30 species occur in India. The insectivorous taxa belong to family Droseraceae (3 spp.), Nepenthaceae (1 spcies) and Lentibulariaceae (36 spp.). The parasitic plant species are prominent in Loranthaceae (46 spp.), Santalaceae (10 spp.), Balanophoraceae (6 spp.), Rafflesiaceae (1 spp.), Cuscutaceae (12 spp.) and Orobanchaceae (54 spp.). Aquatic plants About 2 percent of all flowering plants known in the world inhabit water bodies and more than 50 percent of these are represented in Indian subcontinent (Lavania et al., 1990). Some important aquatic plants families are: Alismataceae (8 spp.), Aponogetonaceae (6 spp.), Azollaceae (1 sp.), Barclayaceae (2 spp.), Butomaceae (1 sp.), Cabombaceae (2 spp.), Callitrichaceae (3 species), Isoetaceae (10 spp.), Lemnaceae (14 spp.), Najadaceae (7 spp.), Nelumbonaceae (1 sp.), Nymphaeaceae (7 spp.), Podostemaceae (24 spp.), Pontederiaceae (13 spp.), Ceratophyllaceae (3 spp.), Hydrocharitaceae (13 spp.), Potamogetonaceae (18 spp.), Ruppiaceae (1 sp.), Salviniaceae (3 spp.), Trapaceae (2 spp.), Typhaceae (4 spp.), Zannichelliaceae (1 sp.), etc. The members of families Podostemaceae and Tristichaceae grow on rocks under water in fast flowing streams. The aquatic plants in India are highly diversified comprising free-floating forms (Eichhornia crassipes, Lemna perpusila, Nymphoides hydrophylla, Trapa natans var. bispinosa, Pistia stratiotes, Wolffia microscopia, W. globosa), rooted aquatics with their foliage floating (Nymphaea nouchali, N. stellata, Euryale ferox, Nelumbo nucifera), submerged aquatics (Vallisnaria natans, Hydrilla verticillata, Najas graminea, Potamogeton pectinatus) emergent aquatics (Scirpus maritimus, Cyperus articulates, Sagittaria trifolia, S. guayanensis subsp. leppula) and marsh plants (Ranunculus scleratus, Hydrolea zeylanica, Panicum paludosum, Polygonum barbatum, P. glabrum). The aquatic flora play an important role as water purifier by absorbing heavy metals, e.g. Ceratophyllum demersum (chromium), Bacopa monnieri (copper and cadmium). Limosella aquatica, Hippuris vulgaris occur in subalpine-alpine lakes. Mangroves Mangroves are the plants that inhabit coastal regions and estuaries. They are adapted to survive under marshy conditions. In India, mangroves cover an area of approximately 6700 Km ² which constitutes c. 7 percent of the world’s mangroves. The largest stretch of mangroves in India occurs in Sunderbans (West Bengal) which covers an area of about 4200 km ². It has been designated as World Heritage site of which 80% of them are restricted to Sunderbans (West Bengal) and Andaman Nicobar islands (Chowdhery and Murti, 2000). The remaining taxa are scattered in the coastal areas of Andhra Pradesh, Tamil Nadu, Orissa, Maharashtra, Gujarat, Goa and Karnataka. Some of the dominant mangrove species include Avicennia marina, A. officinalis, Bruguiera gymnorrhiza, B. parviflora, Ceriops tagal, Heritiera fomes, Lumnitzera spp., Rhizophora mucronata, R. apiculata, R. stylosa, Sonneratia spp., Xylocarpus spp., etc. The shrubby Aegialitis rotundifolia and Acanthus ilicifolius are common o n poor saline plains. The herbaceous succulent halophytes are represented by Aegiceras corniculatus, Suaeda brachiata, Sesuvium portulacastrum and Salicornia brachiata. The characteristic mangrove palms are: Nypa fruticans and Phoenix paludosa. Indicator species Some species of angiosperms growing on metalliferous soils accumulate large amounts of metals in their roots and reflect the levels of metal present in the soil (indicators). For example, presence of copper is indicated by Astragalus spp., Croton roxburghii, Hyptis suaveolens, Holarrhena pubescens, Impatiens balsamina, Vernonia cinerea, and indicates presence of Uranium (Aery, 1977; Venkatesh, 1964, 1966). Diversification of Primitive and Advanced Families The primitive families are confined to those regions which are very old in geological time scale in comparison to the newly developed areas. Assam, North-east Indian region and Deccan Peninsula are older in comparison to the other phytogeographical regions of India. These regions are more or less identical in age with Sri Lanka, South West Chinese region and Malay Peninsula. The Deccan Peninsula shows its floristic relationship with Sri Lanka and Malay provinces, while the North east India shows its floristic relationship with Myanmar, South West Chinese Provinces and Malay Peninsula. Thus the Malay region shows similarity with Deccan Peninsula on one hand and North east India on the other. By this way the North East India shows similarity with Deccan Peninsula to some extent (Mitra and Mukherjee, 2006). India (Eastern Himalaya including North east India) is considered as a sanctuary of primitive flowering plants. The occurrence of such a large number of primitive angiosperms led Takhtajan (1969) to designate this region as the ‘Cradle of Flowering Plants’ where angiosperms have diversified (Table 2) Table.2. Primitive flowering plants occurring in India (after Rao, 1994) The advanced families occur in those areas which are comparatively very young in the geological time scale. On the basis of this idea it can be stated that the Himalayan region of India is very young in its age as compared to Deccan Peninsula and North East Indian regions of India, as it harbours most of the advanced families with well diversified restricted genera and species. A comparative account of diversification of primitive and advanced families of India and its adjoining area is given in table 3. The advanced families are young in their age and also they are confined to the areas which are also geologically young, they are unable to spread in the wider regions. On the other hand, primitive plant families are older in their age and also found to confined in those areas which are geologically very old. So they get sufficient time to spread over larger areas, as a result of which the primitive families show less number of restricted genera and species in their credit in comparison to the advanced families (Mitra and Mukherjee, 2006). Habitats Different ecological habitats occur in India ranging from tropical rainforest, subtropical savanna or shrublands, temperate forest, alpine mosses to xerophytic variation of desert. The habitat types vary from the humid tropical Western Ghats to the hot deserts of Rajasthan, from cold deserts of Ladakh to the long, warm cost line stretches of peninsular India. While Cherrapunji and Mawphlong in the north-eastern state of Meghalaya are the two wettest places on earth, Dras in Ladakh is the coldest inhabited place of the world. Phytogeographically, the eastern Himalaya forms a distinct floristic region. The area comprises Nepal, Bhutan, and neighboring states of northern India along a continuous sector of the Yunnan province in south-west China. In Nepal, there are around 7000 plant species, many of which overlap those of India, Bhutan and even Yunnan. Of these species, at least 500 (almost 8%) are believed to be endemic to Nepal. Bhutan possesses an estimated 5000 species, of which as many as 750 (15%) are considered to be endemic to the eastern Himalaya (Anonymous 1999). This region is the meeting ground of the Indo-Malayan, Afro-tropic and Indo-Chinese biogeographical realms as well as the Himalayan and Peninsular Indian elements, formed when the peninsular plate struck against the Asian landmass, after it broke off from Gondwana land. The region is recognized as refugium of flowering plants and center of active speciation (Rao, 1994). The numerous primitive angiosperm families found in this region inclu de Degeneriaceae, Eupomatiaceae, Himantandraceae, Lardizalbalaceae, Magnoliaceae, Trochodendraceae, Tetracentraceae, Winteraceae. The primitive genera are Alnus, Aspidocarya, Betula, Decaisnea, Euptelea, Exbucklandia, Haematocarpus, Holboellia, Houttuynia, Magnolia, Mangelietia, Pycnarrhena, and Tetracentrol (Malhotra and Hajra 1977). Regions of High Diversity India is one of the 12 mega biodiversity countries of the world. It represents an example of conglomeration of diverse bioclimates influenced by neighbouring areas (particularly Mediterranean), the unique location, peninsular land mass, Gangetic plains and the crown of complex chain of mountain systems – the Himalaya. The Himalayan region with only 18% of India’s land area, houses 81.4% of the country’s stock of gymnosperms, 47% of angiosperms, 59.5% of lichens, 58.7% of pteridophytes, 43.9% of bryophytes and 53.07% of fungi found in India. Orchidaceae with over 1331 taxa (S. Misra, 2007) is one of the dominant families and probably the second largest among all families of flowering plant known from India. Of these 407 taxa are endemic to India. Out of the 18 monotypic orchid genera of India, 13 are found in the Himalayan region. In the Eastern Himalaya, the Orchid family is the largest, with 60% species, whereas in the Western Himalaya, Asteraceae with 540 species is the largest family followed by Poaceae with 439 species and Fabaceae with 362 species. Carex with more than 100 species and infraspecific categories is the largest genus in the Himalaya. Rhododendron with 96 species and infra-specific categories, and Astragalus with 90 species, is the largest genera in the Eastern and Western Himalaya, respectively. Some other plants with pronounced diversity in the Eastern Himalaya include the Hedychium (Zingiberaceae) with 18 species out of 35 Indian species, and numerous species of bamboos. The Eastern Himalaya is a cradle of numerous primitive angiosperms, such as Manglietia and Euptelea (Magnoliaceae) and Tetracentron (Tetracentraceae). Christollea himalayensis, recorded from Mt. Camet is the flowering plant occurring at the highest altitude (6300 msl). Arceuthobium minutissimum, (small angiosperm) grows on Himalayan conifers. Apart from these botanical curios, the Himalayan region has a rich diversity of medicinal and aromatic plants. The floristic richness has also rendered the North-Eastern region and Western Ghats to be recognized as two hotspots among 25 hotspots identified throughout the world. The humid tropical conditions met within these regions not only support exceptionally diverse vegetation but have also resulted in speciation in several genera, thus adding to the high endemicity of the flora (Nayar, 1996). In addition to these two, there are about 40 other sites in different phytogeographical zones of India which have high degree of endemism and genetic diversity. Mc Neely et al. (1990) estimated that 70% of worlds total flowering plants occur in 12 countries and these have been designated as Mega diversity centres or mega ­biodiversity country. The earth’s 25 biodiversity hotspot regions collectively cover about 2% of the planet’s land surface, yet claim more than 50% of all terrestrial species diversity. They have within them a phenomenal 1, 25,635 plant species. The top 11 hotspots (out of 25) for plant endemism harbor 5000 or more species as endemics. It accounts for 93,214 plant species, or 37.3% of the total global plant endemics (Myers 1988). Western Ghats The Western Ghats, which covers an area of approximately 1, 60,000 Km ², are among the 25 biodiversity hotspots globally identified. The wide variation of rainfall patterns in the Western Ghats, coupled with the regions complex geography, produces a great variety of vegetation types. These include scrub forests in the low-lying rain shadow areas and the plains, deciduous and tropical rainforests up to about 1,500 meters, and a unique mosaic of montane forests and rolling grasslands above 1,500 meters. Based on the ecological factors and floristic composition, four major forests and 23 floristic types have been identified. Eastern Himalaya Eastern Himalaya covering the states of Sikkim, Darjeeling district of West Bengal, Assam, Manipur, Tripura, Meghalaya, Arunachal Pradesh, Mizoram and Nagaland is the richest of the phytogeographic regions of India affording the highest plant/ animal diversity (Rao, 1994). This region is characterized by high rainfall and humidity. The abundant rains and high humidity contribute the occurrence of largest number of species in this region. North eastern region of India, blessed with wide range of physiography and ecoclimatic conditions, is the richest biodiversity centres of the Indian subcontinent (Hooker and Thompson, 1855; Hooker, 1905; Chatterjee, 1962; Rao, 1974). The north eastern India has a geographical area of about 2, 55,050 Km ². The rich plant wealth of this region has been reported by Hooker (1854). Further, Hooker’s work on â€Å"Flora of British India† (1872-97) and â€Å"Sketches on Flora of British India† (1905), presents a very detailed account on vegetation and flora of this region. Kanjilal et al. (1934-1940), in their â€Å"Flora of Assam† have provided a detailed account with emphasis on woody flora of this region. There are works on â€Å"Forest flora of Meghalaya† by Haridasan and Rao (1985, 1987) and â€Å"Grasses of North eastern India† by Shukla (1996). There are several genera endemic to Eastern Himalaya. Some important endemic genera are Aucuba, Bryocarpum, Pleurospermopsis, Gamblea, Lepidostemon, Parajaeschkaea, Paroxygraphis, Risleya, Sphaerosacme, Treutlera and Brachycaulos. Cyathopus is endemic to Sikkim. Some genera like Biswarea, Hymenandra, Jejosephia, Neoluffa, Pauia, etc. are endemic to North eastern India. Some important Eastern Himalayan endemic species are Abies densa, Agapetes incurvata, A. sikkimensis, Dipsacus atratus, Eriobotrya hookeriana, Geum macrosepalum, Larix griffithiana, Lindera heterophylla, Liparis perpusilla, Lloydia flavonutans, Maddenia himalica, Meconopsis grandis, M. superba, M. villosa, Myricaria albiflora, Primula whitei, Rhododendron baileyi, R. camelliaeflorum, R. ciliatum, R. glaucophyllum, R. grande, R. lantanum, R. lindleyi, R. wallichii, R .wightii, Rubus fragarioides, Sassurea conica, Acanthus leucostachys, Aconitum assamicum, Anoectochilus sikkimensis, Aeschynanthus parasiticus, Baliospermum micranthum, Berberis dasyclada, Calamus leptospadix, Calanthe densiflora, Capparis acutifolia, Cotoneaster assamensis, etc. (Chowdhery and Murti, 2000) Plant Diversity in Western Himalaya The Western Himalayan region is one of the 12 biogeographic regions of India and includes Jammu and Kashmir, Himachal Pradesh, and Uttaranchal. This region constitutes the alpine zone, temperate, humid and warm climatic conditions. The main portion of Western Himalaya lies in J K state comprising 67.5