Tropical grassy biomes (TGBs) cover a substantial portion of Earth's land surface area and support a rich diversity of fauna and flora. Yet, despite their importance for biodiversity and human livelihoods, the TGBs of South Asia, including India, have historically been ecologically and economically undervalued, and as result, understudied. Here, we address this gap with the first subcontinental-scale analyses of grass species (Poaceae) richness and distribution across the Indian region. Using data on species occurrences collated from multiple regional floras, we describe the distribution of families, functional groups and species of Poaceae across this region, and their variation as a function of climate and geomorphology. India hosts > 1100 grass species, comprising similar to 10 % of global grass richness. Over half of these were perennial C-4 grasses, with Panicoideae being the most speciose subfamily in the country. Consistent with patterns observed globally, the PACMAD clade consisting of both C-3 and C-4 species was more speciose in warmer regions, while the C-3 subfamilies of the BEP clade, Pooideae and Bambusoideae, were more abundant in cooler regions of the country. Both total and C-4 species richness were greatest in warmer districts with high moisture availability, while cooler and wetter districts with low precipitation seasonality supported greater C-3 species richness. Our results spotlight previously unrecognized areas of high Poaceae richness in the arid and semi-arid areas of North-West India and the Deccan Peninsula in India, and call for conservation attention to neglected regions that are outside known biodiversity hotspots and protected areas.