The present study was aimed to evaluate adaptive mechanism in terms of seed characters of Phyllanthus amarus collected from ten different locations of Tamil Nadu, India. The adaptive variations among the collected populations were assessed based on the sink and float percentages of the seeds in water, the percentage of seed germination, total protein, carbohydrates and their seedling's growth ability such as shoot and root lengths. From this, we observed that the population had a significantly higher germination percentage of sinking seeds that were attributed to its relatively higher carbohydrate and protein contents than the floating seeds. A comparison of the seed population by cluster analysis and principal coordinate analysis showed that the Chennai population constituted a single clade that was very distinct from the other nine populations, which were further grouped into two sub-clusters. They exhibited a trend consistent with their geographical proximity. Standardised Mantel's t tests had revealed that the adaptive diversity of the P. amarus population was significantly affected by the geographic distance (r = 0.78, t = 2.68, P > 0.001), altitude (r = 0.35, t = 21.53, P > 0.05), minimum temperature (r = 0.43, t = 1.49, P > 0.01) and maximum temperature (r = 0.49, t = 1.67, P > 0.001). Seed's characteristics and geographical conditions were correlated along with 19 bioclimatic variables. In dry season, the seedling's rooting ability showed positive correlation, while its protein content exhibited a negative correlation. It is clearly evident from this study that the geographical variables significantly influence the adaptive ability of the P. amarus.
Keywords: Geographic variation; Mantel’s t test; PCoA analysis; Phyllanthus amarus; Population diversity.