Hear me out. The Vinaya says that the Middle Country is bounded to the north by a mountain called Usīraddhaja (pli-tv-kd5:13.12.6). This means “crest of vetiver”.
While the mountain is not exactly identified, there are several references.
Probably it’s somewhere up towards Kashmir. In fact, if we are to actually bound the Indian cultural sphere, it would be the range known today as the Hindu Kush.
Now, Wikipedia says the name “kush” is uncertain. The most obvious candidate would be the grass known as kusa or dabbha (or dabba) in Pali, kuśa or darbha in Sanskrit. But this is ruled out because these are lowland grasses that don’t grow in the arid, rocky climes of the Hindu Kush.
There’s another odd detail here. Some sources also connect this region with dārva, “the name of a tribe mentioned as inhabiting the region around ancient Kaśmīra (Kashmir valley) according to the Nīlamatapurāṇa”.
But could dārva be a local variant of darbha? If so, does this mean that for the mountainous regions at the north-west extremity of the Indian subcontinent we now have three names for grasses?
Now, call me crazy but doesn’t vetiver look a little bit like a mountain range, with the crests like the snow caps?
Perhaps the Hindu Kush, Dārva, and Usīraddhaja are all the same, named for the appearance of the mountains from the plains, looking like giant clumps of tall grasses crested with snow-like flowers?

