The local Chinese store was out of daikon so my husband (knowingly) bought a root that looked similar. He thought it would either be a good substitute or a good adventure.
The root is long like daikon but with a thin brown skin and roots, like many potatoes. Cutting into it revealed a gooey substance inside.
Fortunately, if you Google “sticky Japanese root”, yamaimo is the only result. They are sometimes also called “Japanese yams.”
Tasting them raw, they have a mild watery flavor but also a tangy taste. The taste is a little similar to dragonfruit, but starchy like a potato. I really like it.
According to this website, yamaimo are ancient roots with short grow seasons, making them fairly rare: http://www.favy-jp.com
Fortunately, I found a recipe for how to prepare them on Just One Cookbook: https://www.justonecookbook.com/sauteed-yam/
It recommended sautéing the yams with soy sauce. I also mixed them with the eggplant and zucchini that my husband had bought for dinner.
The result is SO TASTY! Next time I see yamaimo at the store, I will definitely buy them again!