HABITAT AND PHYTOSOCIOLOGICAL CHARACTERS OF THE ENDANGERED PLANT SPECIES, EXACUM BICOLOR ROXB.

Study on the phytosociological characters like distribution, abundance, density etc of a species in its established habitats is a tool to determine the effect of environmental conditions on variations in population characteristics. Based on this concept, four leaf shape variants (ovate, linear- lanceolate, oblanceolate and ovate – elliptic) of the plant species, Exacum bicolor distributed in four different grasslands habitats viz.,Payyanur, Taliparamba, Paithal mala and Thirunelli at Kannur and Wayand districts of Kerala were selected in the present study. The populations of the study species showed distinct expression of ecological attributes across the four leaf shape variants in four habitats studied. The distribution level determined through the annual mean frequency percentage was higher (89.29 %) in the populations of ovate leaf shape variant in Taliparamba, where as it was lower (5.71 %) in the populations of linear – lanceolate leaf shape variant in Payyanur. Similarly, the annual abundance of the population was higher (5.08/m2) for ovate – elliptic leaf shape variant (Taliparmba) and lower (1.43/m2) for linear – lanceolate leaf shape variant (Thirunelli). The annual density obtained by the population was also higher for ovate leaf shape variant present in Taliparmba (4.10/m2) and lower for the population of linear – lanceolate leaf shape variant present in Thirunelli, (0.09/m2). From these ecological studies, it is understood that among the four leaf shape variants, generally ovate leaf shape variant has established well. In addition, the grassland community at Taliparamba is determined to have most suitable microclimate also for this variant than the other habitats studied.


INTRODUCTION
Exacum bicolor (Family: Gentianaceae) is an endangered medicinal herb distributed in hillocks of northern Kerala between the altitude 50-200 m above MSL. Unique feature of this plant is limited dispersion with very few individuals in large stretch of grasslands. (10,11). In addition, in the districts of northern Kerala like Kannur, Wayanad, Calicut, Palakkad etc this species is represented by four ecological variants on basis of leaf shape such as ovate leaved, linear-lanceolate leaved, oblanceolate leaved and ovate-elliptic leaved.
E. bicolor have high ornamental value and in Kerala, it is in use of different ailments since many centuries. Whole part of the plant is used as a tonic, febrifuge and stomachic and antifungal agent (7,13,5,2,9). The plant also yields dye also (12). Being bitter in taste, local people take it as herbal remedy for diabetes, and skin disorders (8). In Kerala, the traditional practitioners prescribe decoction of the whole plant for the treatment of fever, eye and skin diseases and urinary disorders. Traditional healers of Pundra and Bilaspur regions of Chhattisgarh use this plant as blood purifier and for the treatment of malaria. Flowers of this plant were given great religious importance in old Valluvanadan region of Kerala. It is one of the choicest flowers to adorn Trikkakkarayappan, the earthern diety worshiped during Onam an important regional festival. Except few works on distribution status, no ecological studies have been carried out for this species. Hence, to know the status of the degree of distribution, density and abundance the present works has been done in all the four leaf variants.

MATERIALS AND METHODS
Phytosociological studies for the four leaf shape variants of the species, Exacum bicolor were carried out for a period of seven months from May, 2009 to November, 2009 at monthly intervals in all the four studied grasslands of Kerala viz., Taliparamba (55m above MSL), Payyanur (15m above MSL), Paithal mala (1350m above MSL) of Kannur district and Thirunelli (900m above MSL) of Wayanad district. The minimum quadrat size of 1 x 1m was fixed by the species-area curve method, and each time, 20 quadrats were laid by randomized method. The minimum number of quadrats (i.e. 20) was determined as described by Greig -Smith (1). For this, the mean number of individuals of the first five, ten, fifteen, twenty, etc., *Correspondence: Paulsamy, S., Department of Botany, Kongunadu Arts and Science College, Coimbatore, Tamil Nadu, India. quadrats were calculated and plotted against the number of observations. It will be seen that the mean at first fluctuates, steadying as the required number of quadrats was reached.
The number of individuals of all the four leaf shape variants of E. bicolor in each quadrat was recorded. From the observations, the quantitative characters such as frequency, density and abundance were calculated using the following formulae:

RESULTS AND DISCUSSION
The study on local distribution revealed that the four ecological variants of the study species, Exacum bicolor are site specific (Tables 1). The ovate, oblanceolate and ovate-elliptic leaf shape variants of E. bicolor are noted to be present in Payyanur and Taliparamba grasslands and linearlanceolate leaf shape variant has distributed in Paithal mala and Thirunelli grasslands. In early study, (11) also reported the site specific distribution of variants of this species in northern Kerala. This may be explained due to the microclimatic preferences of the variants at soil level (10 Table 2). On the other hand, the Paithal mala and Taliparamba grasslands hold respectively the linear -lanceolate leaf variant and oblanceolate leaf variant with more area of distribution. The Taliparamba grassland also encompassed the ovate-elliptic leaf variant with higher area of distribution. Odum (4) pointed out that the differences in macroclimatic conditions and certain microclimatic factors like the availability of soil moisture due to the angle of slope etc may influence the distribution of any species within the biome. Further, it is known from the present study that the ovate leaf variant of the study species recorded higher area of distribution than the other leaf variants studied. It may be explained due to the fitness of this variant in the natural herbaceous communities of northern Kerala in terms of germination and adaptability.     -------Payyanur  55  80  95  100  95  95  65  Taliparamba  65  85  100  100  100  100  75  Thirunelli  -------Linear-lanceolate leaved  60  60  75  100  65  50  65  Paithal mala  -------Payyanur  -------Taliparamba  5  5  5  10  5  5  5  Thirunelli  Oblanceolate leaved  Paithal mala  -------Payyanur  45  60  75  100  80  65  65  Taliparamba  50  65  75  100  90  70  65  Thirunelli  -------Ovate-elliptic leaved  Paithal mala  -------Payyanur  55  70  80  100  90  75  60  Taliparamba  65  75  85  100  100  70  55  Thirunelli  ----    The density is the most important quantitative character of any species in a community to know its structural and functional contribution to the ecosystem. In addition, the determination of density for a species or variant is more useful to know its microclimatic preferences in a common macroclimatic condition.
In homogenous community, the density character is used to find out the dominant species also. The annual density obtained by the population was also higher for ovate leaf shape variant present in Taliparmba (4.10/ m 2 ) and lower for the population of linearlanceolate leaf shape variant present in Thirunelli (0.09/ m 2 ) ( Table 4).
In the present study, the density of all the four leaf variants of the study species, E. bicolor was increasing during rainy season. It is of common fact that in tropical and subtropical regions, the limiting factor, soil wetness increases the seed germination and stock sprouting rates and hence the density during rainy season for almost all species in a community (3). The enhancement of density for the studied four leaf shape variants was site specific i.e .ovate, oblanceolate and ovate-elliptic leaf variants attained higher densities in Taliparamba grassland. The linear-lanceolate leaf shape variant showed its higher density in the grassland of Paithal mala. It indicates the specific fitness of these variants to the above mentioned grasslands in respect of density. The pH, angle of slope in the respective grassland, content of micronutrients in soil and intensity of light available in the grasslands may be the possible factors for this fact (6). Vijayakumar (14) also reported the site specific preference of leaf variants of the medicinal plant, Gaultheria fragrantissima in the shola grasslands of Nilgiris. On basis of density, it is known that the Taliparamba grassland was found to have more favourable factors and condusive environment for the growth, reproduction and perpetuation of the study species E. bicolor particularly for the ovate leaf shape variant.

CONCLUSION
Based on the ecological attributes like frequency, abundance and density studied, it is understood that among the four variants, generally the ovate leaf shape variant of the species, E. bicolor has established well. In addition, the grassland community at Taliparamba is determined to have most suitable microclimate also for this variant than the other areas studied. Therefore, if any cultivation attempts will be made in future on demand, the Taliparamba habitat and other habitats similar to Taliparamba may be preferred partially for ovate leaf shape variant.