There is a plant very similar to jicama but a little smaller, sweeter and more tender. In West Bengal it's called shankh alu (শাঁখ আলু) although I could swear I heard it called shakar alu (literally "potato of the spinach"). Basically it seems to be a cultivar of jicama or Pachyrhizus erosus.
I'm wondering if anyone has found any of the smaller and sweeter Asian varieties here in the US?