A Himalayan monsoon location exhibiting unusually high preponderance of C4 grasses.
An unexpectedly large proportion of C4 grasses was found in a moderately temperate and moist Himalayan location (32°N., 76°E) near Palampur during the monsoon period. 79% of total grasses found in the area were of the C4 type. Desmostachya bipinnata, Eragrostis atrovirens, E. tenella, Leptochloa chinensis, Digitaria stricta, Panicum psilopodium, Paspalidum flavidum, Setaria homonyma, S. paniculifera, S. tomentosa, Arundinella bengalensis, Chrysopogon fulvus, Eulalia leschenaultiana, Narenga porphyrocoma, Saccharum spontaneum, Sorghum nitidum, Themeda anathera, Hemarthria compressa and Rottboellia exaltata [R. cochinchinensis] were newly recorded as C4 species. The origin of the C4 pathway has been attributed to low atmospheric CO2 concentration during the palaeocene and miocene. The latter period corresponds both to the origin of grasses and the formation of the Himalayas. It is suggested that the reason for the preponderance of C4 species in this location is the apparently low ambient atmospheric CO2 concentration. It is suggested that low ambient CO2 concentration is the primary environmental cue for an abundance of C4 species.