Observations on the flowering plant diversity of Madayippara, a southern Indian lateritic plateau from Kerala, India

Northern Kerala of southern India is characterized by widely spread lateritic plateaus which provide an extremely harsh physical environment for life leading to the development of specialized plant communities with a large number of endemic and habitat specific species. Madayippara, a midland lateritic plateau located in the Kannur District of northern Kerala is an icon of rich floristic diversity and endemism. The plateau forms a number of microhabitats due to the difference in geographic terrain and soil cover, thus forming a complex of habitats with diverse forms of plants, mainly ephemeral herbs. Out of the 636 flowering plant taxa recorded from the microhabitats of the plateau, within a limited area of 3.65km2, 160 (c. 25%) are endemics. Most of the endemic species occur in specialized microhabitats. The plateau is the type locality of 11 taxa. Lateritic plateaus of southern India, which are associated with characteristic and rich biodiversity, are now under varied types of anthropogenic threats such as large scale mining for bricks and clay, and they need urgent attention for conservation of the biodiversity.


INTRODUCTION
In India, the hard crusts of laterite are mainly found on the western coast, from Dapoli in Ratnagiri in Maharashtra to Malappuram District in Kerala, and also on the Deccan Plateau (Balakrishnan et al. 2011). Distribution of laterite in Kerala, is mostly confined to an elevation of less than 600m, forming low flat topped ridges and hills, between the foothills of the Western Ghats and the Arabian Sea, mainly from Malappuram to Kasaragod (Varghese & Byju 1993). In the geographical documentation of the Government of Kerala these landscapes are marked as 'wastelands' (Anonymous 2019). The laterite hills are the most imposing feature of northern Kerala, which are extremely threatened both in terms of topography and biodiversity (Muraleedharan 2011). These plateaus are characterized by extremely harsh environment such as high temperature and lack of moisture content in the summer, leading to the development of unique vegetation, many of which show special adaptation to the environment. These severe conditions play a decisive role in the development of seasonal vegetation, where most of the plant species complete their life cycle during the monsoon period. When compared with granitic inselbergs (granitic rock outcrops), the vegetation and flora of lateritic plateaus has many unique peculiarities. The present study is an effort to record the floristic diversity and endemism of the Madayippara lateritic hillock in Kannur District of Kerala.

Study Area
Madayippara, a good representative of the southern Indian midland lateritic plateaus, is located in Madayi Panchayath, near Payangadi Town in Kannur District of Kerala, southern India. The plateau covers an area of 3.65km 2 , between 12.01-12.05 0 N and 75.23-75.27 0 E, at an altitude of about 50m from the mean sea level ( Fig.  1; Image 1-3). The climatic conditions vary from hot dry to warm humid in different seasons, viz., pre-monsoon (March-May), monsoon (June-November), and postmonsoon (December-February); these together with edaphic factors account for the development of characteristic vegetation, as observed by Muller (2007).

Methods
Intensive field visits were carried out at Madayippara lateritic plateau covering all seasons during the period 2008-2017 to document floristic diversity. Different microhabitats on the plateau such as seasonal pools, soil covered areas, rocky surfaces, and tree associated vegetation along the valleys were surveyed repeatedly at different seasons and specimens were collected for laboratory studies and for the preparation of voucher specimens. Photographs of plants and habitats were taken using Nikon Coolpix L110 and Olympus C-7070 cameras. The voucher specimens were prepared following the wet method (Fosberg & Sachet 1965). The specimens were pressed in blotting paper, dried in a hot air oven, mounted on standard size, hand-made herbarium mount boards using a synthetic gum (Fevicol SH) and labeled and deposited at Calicut University Herbarium (CALI), duplicates of which are deposited at the herbarium of the Government Brennen College, Thalassery, Kerala. The specimens collected for laboratory studies were worked out using a LEICA M80, ZEISS Stemi DV4 and LABOMED CSM2 microscopes and identified using pertinent floras and relevant revisions and monographs; and by comparison with the specimens available at Calicut University Herbarium (CALI), Madras Herbarium (MH) and with the images in the Kew Herbarium (K) Catalogue (http://apps.kew.org/herbcat/navigator.do). Some of the specimens were referred to concerned experts in India and abroad for the confirmation of J TT identification. The literature on phytogeography and endemism were referred to assess the distribution and endemism of each species. Conservation status of each species was checked with the available assessed data as per the IUCN Red list Categories and Criteria Version 3.1 (IUCN 2012). Endemism of taxa were recorded based on previous publications such as Sasidharan (2004) and online databases such as World Checklist of Selected Plant Families (http://apps.kew.org/wcsp/home.do). Botanical names were updated using online databases like The International Plant Names Index (IPNI) (http:// ipni.org/ipni/plantnamesearchpage.do) and World Checklist of Selected Plant Families (http://apps.kew. org/wcsp/home.do) of the Royal Botanical Gardens, Kew.

RESULTS AND DISCUSSION
The vegetation of Madayippara lateritic plateau is divided into four broad categories with the characteristic flora associated with each of them (Jacobi et. al. 2007, modified). The plant species in the microhabitats are adapted to sustain in the adverse environmental conditions, such as seasonal drought, high temperature and nutrient scarcity. It has been observed that there is an overlap between most of the species in microhabitats with varying degree of dominance, as stated by Watve (2013), however, some species are always restricted to a particular microhabitat. Bhattarai et al. (2012) in a study on the mesoscale distributions of endemic, rare, or locally important plant species on the plateau habitats and its escarpments, assessed the hydrological and edaphic parameters of seasonal plateau microhabitats on the Kas Plateau in Maharashtra. They found that almost two-thirds of over hundred phytogeographically important species occur on the plateau top. Since botanically critical plateau habitats are generally small, dependent on seasonal moisture of monsoon, and determined by drainage-related parameters that are altered by anthropogenic activities, they are highly threatened. Using the Kas region as a model lateritic system, they assessed its significant flora and habitats at two scales: mesoscale distributions in major ecological zones of the plateau and its subtending slopes, and microscale distributions on the plateau in seasonal habitats defined by hydrogeomorphic parameters such as moisture content, seasonal water retention capacity, profile of the soil, topographic variation, depth and texture of soil, and micro-elevational gradients. They identified 11 microhabitat types on the plateau top, that support varieties of plant species of phytogeographic significance during the monsoon. The plateau consists of a mosaic of floristically different habitats determined by hydrogeomorphic factors; for many of these habitats, the occupied area is very small in extent and seasonally ephemeral.
In a similar floristic analysis conducted in 10 threatened high altitude lateritic plateau ecosystems including Kas in the southwestern Maharashtra part of Western Ghats, Lekhak & Yadav (2012) recorded the presence of 361 taxa of herbaceous plants. Out of the reported 67 endemic species from the study area, 39 are restricted to lateritic plateaus only. They also identified 11 microhabitat types that support distinct plant communities depending primarily on the availability of soil and moisture. The plant communities of these J TT habitats are usually edaphically controlled and show adaptation for water accumulation, such as succulence and poikilohydry, carnivory in response to the lack of nutrients in the soil and the presence of underground organs to overcome extreme temperature during summer.
The studies discussed above are from high altitude lateritic plateaus of the northern Western Ghats, and the area surveyed is large compared to the present study, however, climatic and geomorphologic characteristics of the microhabitats are found to be important for the distribution of endemic species in all cases. In a small area, strong endemic component in the flora is associated with seasonal moisture availability. These endemics occur in a variety of ephemeral microhabitats associated with edaphic features of the plateau (Bhattarai et al. 2012). In the present study, microhabitats are included in broader categories, as more emphasis is given to the floristic documentation of the entire plateau habitats and its escarpments. As tree cover and scrub patches on and around the plateau sustain more number of plant species, they support more number of endemic species.
(1) Exposed rock surfaces and crevices (RC): Laterite rock surfaces form one of the most important habitats that support a number of species adapted to this habitat. The micro environment of the lateritic rock surface and crevices are extremely different from that of the surrounding soil covered areas. The rock surfaces are characterized by very low moisture content, high thermal variation, very low organic carbon content and less availability of nutrients. The crevices and fissures on the rocks show the presence of little soil. A few of the plant species growing on exposed rock surfaces are desiccation tolerant.
(2) Seasonal ponds and small ephemeral pools (SP): During rainy seasons small and shallow ephemeral pools and some large ponds are formed on the plateau. These support a large number of hydrophytes including endemic species showing various degrees of rarity. The seasonal pools in the plateau are varying in their area, depth, soil cover and soil texture. The pools are just depressions on the plateau, either on laterite rock or on soil covered areas. If it is on rocks, thin layers of soil, rich in organic matter has been noted, which support the vegetation. The pools get dried up in postmonsoon periods and remain dry till pre-monsoon. They become water logged with the onset of southwest monsoon and dry up after the retreat of the northeast monsoon. Water in the seasonal pools is subjected to extreme diurnal changes in temperature due to the high surface to volume ratio (Pramod 2015 (3) Soil covered areas and grassy plains and slopes (SC): Surrounding the rocky surfaces are the areas with soil cover of varied thickness from less than 1cm to more 1m, and on the southeastern part of the plateau grassy slopes with thick soil cover occur. The vegetation of the soil covered areas varies slightly depending on soil thickness. The areas with low soil thickness, which usually hold higher moisture content in the early monsoon are characterized by ephemeral flush vegetation, that are later replaced by grass and sedge species.
(4) Tree cover and scrub patches (TS): The upper flat terrain of the plateau, which is almost devoid of thick vegetation, is surrounded by tree vegetation of varying characteristics, from scrub jungles to thick semi evergreen forests. These forest patches are highly diverse with respect to species composition and the presence of endemic and rare elements. Though the top of the plateau is devoid of continuous tree cover, some isolated tree species are found. There are small scrub patches with short trees, shrubs and herbs. Madayikkavu is a sacred grove covering an area of 0.005km 2 with vegetation mainly composed of trees, shrubs, and climbers. A total of 636 taxa of flowering plants, under 110 families, 406 genera, and 631 species were documented from the plateau. They are listed in the Table 1, with the families arranged according to APG system of classification (APG IV 2016). The genera and species are arranged in alphabetical order under respective families and genera. The area of the plateau is very small (3.65km 2 ), representing less than 0.01% of Kannur District, but it harbors about 59% of the flora of Kannur District (Ramachandran & Nair 1988). The immense diversity of flowering plants in Madayippara is due to the occurrence of diverse types of microhabitats and the ecological factors acting on them. The occurrence of a high percentage of endemic species belonging to diverse families in a small area indicates the complex nature of the habitat.
The substrata of the plateau are highly variable ranging from the deep soil profile of grasslands in the valleys to the ultra-thin film of humus on the exposed rock surfaces. In rock surfaces, the vegetation is very distinct with the predominance of drought tolerant species. The fine dust and humus accumulated in the vermiform tubes and cavities of the laterite rock provide nutrients to the supporting herbaceous vegetation. Species such as Lepidagathis keralensis, Euphorbia deccanensis, and Polycarpaea corymbosa occur on open lateritic surfaces mostly rooted in the humus rich crevices of the laterite rocks. The plateau is subjected to high degree of seasonal variation in the vegetation and flora. The most important factor that determines the vegetation is the soil moisture content. In the premonsoon period, the open plateau is looking almost barren with few dried grass species of the post-monsoon period. The germination of the seasonal vegetation starts with the summer shower in May and continues later at the onset of south-west monsoon in June. The early monsoon is dominated by ephemeral flush vegetation, which is taken over later by grass and sedge species at the end and continued in the post monsoon period. The monsoon months (June-November) shows the peak of flowering of species, due to the appearance of ephemeral species, grasses and sedges in the open plateau, as shown in Figure 1. In the pre-monsoon and post-monsoon months, flowering is dominated by woody species in the scrub patches and tree cover.

Rarity and endemism
Western Ghats harbours around 1,600 endemic plant species (Nayar 1996), which are documented by many workers, but the diversity and endemism of midland lateritic hillocks and wetlands are seldom documented. Out of the 636 taxa recorded from Madayippara, 160 (c. 25%) are endemics (Table 1). Since the maximum number of plant species were recorded in the tree cover and scrub patches, they hold highest number of endemic species also. Many of the endemic species occur in specialized microhabitats. For example, species such as Lepidagathis keralensis is restricted to hard lateritic rocks with extreme xeric environment; Coelachne madayensis occur in seasonal pools in well exposed sunny locations with submerged foliage and emergent panicles; J TT     Euphorbia deccanensis grows with its roots firmly attached to the humus-rich small cavities and fissures of laterite rocks and species of Utricularia in seasonal pools or shallow soil areas with high moisture content. The high diversity and endemism of the plateaus is attributted to be a general phenomenon and is explained in different plateaus in the Western Ghats region by various authors (Joshi & Janarthanam 2004;Porembski & Watve 2005;Bhattarai et al. 2012;Lekhak & Yadav 2012). Of the 10 taxa described from the study area by different authors, five species, viz., Rotala malabarica, Justicia ekakusuma, Fimbristylis pokkudaniana, Coelachne madayensis, and Chrysopogon narayaniae are endemic to this plateau. The microhabitats, viz., soil covered areas and grassy plains and slopes (SC) and tree cover and scrub patches (TS) hold largest numbers of species and endemics, since they occupy bulk of the total habitat with favorable environmental conditions. Though the number of species including endemics are comparatively less in the other two microhabitats, viz., exposed rock surfaces and crevices (RC) and seasonal ponds and small ephemeral pools (SP), their percentage of endemics is very high (

Threats and Conservation
The highly specialized habitats and rare biodiversity of the coastal lateritic plateaus and hills, parallel to the Western Ghats, have been neglected by scientists and policymakers, until recently. The laterite biodiversity is an unexplored treasure that is being endangered due

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to a multitude of anthropogenic activities. The lateritic plateus of northern Kerala, together with their rich flora and microhabitats are subjected to varied types of pressures such as large scale clay and brick mining, construction works, land filling, seasonal fire, tourism, waste dumping, together with biotic pressures such as invasion of exotic weeds and grazing. As pointed out by Muraleedharan (2011), degradation of lateritic plateaus results in the simultaneous destruction of atleast three ecosystems: lateritic plateaus, valleys and wetlands, which may eventually adversely affect ground water availability.
The discovery of many plant species and high degree of endemism made Madayippara lateritic plateau a 'micro hot spot' for conservation. The conservation efforts in the southern Western Ghats region are mostly restricted to the forested areas, totally neglecting the biodiversity rich lateritic plateaus. The rich biodiversity together with the threats associated with the area (Image 5) demands the need for conserving the area on a war footing. Priority of conservation should be given to endemic species which are short-lived and habitat specific; otherwise, they will be lost forever. The high conservation value of lateritic plateus of southwestern India has been already recognized (Watve & Thakur 2006;Lekhak & Yadav 2012;Bhattarai et al. 2012;Watve 2013). The open areas with herbaceous vegetation and grasses are of importance to bird populations including a large number of rare and migratory species, as they provide better visibility for being vigilant to predators and free movement for food gathering (Desai & Shanbhag 2012). Few afforestation efforts, that are in progress in the plateau are to be discouraged, as the tree species might affect the native herbaceous species because of their dense canopy and allelopathic effect.
The present study recommends conservation of this plateau and similar habitats of northern Kerala, in a similar way as proposed by Chandran et al. (2012), to declare Bhatkal and Mugali laterite plateaus of Uttara Kannada of Karnataka State under 'Conservation Reserves'. The Government should formulate strict rules for the restriction of mining and construction activities in the laterite areas. There is a need to create greater awareness of the importance of laterite hills and their biodiversity among the local community, tourists and policy and decision makers. Extensive floristic studies in similar habitats of northern Kerala are very likely to yield many more new and interesting species.

CONCLUSION
Lateritic plateaus are unique due to the nature of substratum and the extreme environmental conditions. Various microhabitats support a rich floral diversity with a large number of rare and endemic species. Though Madayippara represents an area of less than 0.01% of the total area documented in the Flora of Cannanore District, it harbors about 59% represented in the district flora. The species richness of this area is contributed by the presence of many specialized microhabitats and associated flora. Various microclimatic conditions play a collective role in the development of a particular plant community in a microhabitat. Madayippara lateritic plateau, which is the type locality of 10 taxa, and home for many endemic and threatened species, is highly threatened and urgent measures are to be taken for its conservation. Any slight disturbance in the micro ecosystems can easily take away a number of short-lived herbaceous species which cannot be easily conserved outside its natural habitat. For the conservation of the rich diversity and microhabitats of the plateau, in situ conservation of the entire habitat is the only answer as ex situ conservation measures cannot provide complex microclimatic requirements artificially. www.threatenedtaxa.org The Journal of Threatened Taxa (JoTT) is dedicated to building evidence for conservation globally by publishing peer-reviewed articles online every month at a reasonably rapid rate at www.threatenedtaxa.org. All articles published in JoTT are registered under Creative Commons Attribution 4.0 International License unless otherwise mentioned. JoTT allows allows unrestricted use, reproduction, and distribution of articles in any medium by providing adequate credit to the author(s) and the source of publication.

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