Jinenjo is a variety of the Japanese yams called “Yamaimo.”
They have rough skin; the flesh inside is white, and starchy to the point of being mucilaginous.
Old-timers swear that the Jinenjo yams cultivated these days are not as good as the ones that used to be gathered from the wild. The ones gathered from the wild are long and thin, and have a darker-brown skin.
Jinenjo is slightly sweeter and starchier than another popular variety, Nagamio.
Jinenjo is often served raw in small, fine pieces, or grated for use as an ingredient.