The occurrence of C3 and three different subtypes of C4 photosynthetic pathways in the 1,263 Indian grasses was surveyed using a combination of taxonomic and anatomical criteria. All species of the subfamilies Pooideae, Bambusoideae and Oryzoideae are C3. Some arundinoid and panicoid species are C3 while others are C4. All members of Chloridoideae are C4. The C3, NADP-ME, NAD-ME and PEP-CK pathways occur in 536, 504, 132 and 59 species. The all-India C3: C4 ratio is 3:4. In the high altitude Himalayan region this ratio is 4:1 while it is 1:4 in the rest of India. Two grass Domains are recognized: the Temperate Himalayan Domain is dominated by C3 species, mostly pooids, while the Peninsular Domain has mostly C4 grasses. A transitional region occurs in north-east India. Within the C4 species NADP-ME, NAD-ME and PEP-CK subtypes occur in 8:2:1 ratio. This ratio is characteristic of Indian C4 grasses in a wide variety of habitats including the ten Botanical Regions, and also among the endemic species. Cold temperature favors growth of C3 species; aridity and salinity promote NAD-ME species, and PEP-CK species are common in wetlands. These findings are analyzed in relation to the origin of Indian grass flora, phytogeography and seasonal availability of fodder for grazing animals.

Key words: ecology, Indain grasses, photosynthetic pathways, Poaceae