Pattern of distribution of angiosperm plant richness along latitudinal and longitudinal gradients of India

We analyzed a national database on plant richness with 7761 species from 15,565 nested quadrants to offer the maiden and indicative plant richness pattern of India across its latitudinal and longitudinal gradient. We observed two peaks in the species richness curves along both latitudinal and longitudinal gradients, due to harbouring of higher species richness in the Western Ghats and the Himalayan hot spots. The bands at 10 degrees-11 degrees N latitude and 76 degrees-77 degrees E longitude accommodate maximum of 703 and 864 number of plant species respectively, which could be explained due to cumulative contribution of (i) the Western Ghats, Eastern Ghats, Lakshadweep and Andaman and Nicobar islands along latitudinal; and (ii) the Western Ghats, central India and the Western Himalaya along longitudinal gradients. On dissection of the relationship between plant richness to environment (i.e., geographic area, topography and vegetation types) using Generalized Additive Model (GAM), we observed varied explanations for latitude and longitude. While geographic area and topography explained (98.8% deviance) to the species richness pattern across longitude, all three explained (99% deviance) to the distribution pattern along latitude. We also found that the species richness and vegetation types are positively correlated. Environmental heterogeneity, especially geographic area, topography and disturbance explain the distribution pattern of plant richness in India. Knowing the spatial pattern of plant richness could help in formulating large-scale conservation measures for India. It is hoped that the study would attract larger readership, particularly the Indian bio-geographers.