Dear AS: Darwin speaks of roots being ground. Doesn't make sense to me to speak of a melon having edible roots. I was surprised to find "Casava" originally name of a place in Turkey.
casaba
n.
5after Kasaba, former name of Turgutlu, Turkey, whence the melon came6 any of a group of cultivated melons (Cucumis melo var. inodorus) with a hard, yellow rind and sweet, usually white flesh; winter melon

Just to confuse things further, look at definition of "tapioca":
tapioca
n.
5Port & Sp < Tupi & Guarani typyoca < tipi, dregs + ok, to squeeze out6
1 a starchy, granular substance prepared from the root of the cassava plant, used to make puddings, thicken soups, etc.
2 pudding made from this substance

"If you're not confused, you just don't understand the situation."