Meh...
Purple and dark coloured plants aren't that unusual around even the Lao-Isan region of the Mekong. I've seen them from highland Central Laos hill tribe stuff and in bricked commercial ganja, many times
If, as you claim, you find more of them the further north you go in Thailand, well, guess what, it gets pretty cold at night in the north from at least November onwards, same as in highland Laos...
Purple and dark coloured plants aren't that unusual around even the Lao-Isan region of the Mekong. I've seen them from highland Central Laos hill tribe stuff and in bricked commercial ganja, many times
If, as you claim, you find more of them the further north you go in Thailand, well, guess what, it gets pretty cold at night in the north from at least November onwards, same as in highland Laos...