We found these sweet potatoes growing wild near our bungalow in the South of Thailand and cooked them in the embers of a garden fire whilst we went out for the evening. They were cooked to perfection when we got back home.
Sweet Potato Plants
Sweet potatoes love the tropical heat and sandy dry soil. They grow as a vine an once established they pretty much never go away. The orange and purple varieties are different species.
Sweet Potatoes in Thai Cusine
The purple yams are sweeter than the orange ones and feature heavily in South East Asian dessert dishes. In Thailand the orange ones are used more commonly in curries and feature more heavily on restaurant menus. You are more likely to find the purple variety being sold at sweet (khanom wan) stalls. If you get hold of raw sweet potatoes try baking them on the fire they are awesome.