My source for these groundnut was Will Bonsall's SCATTERSEED project. Wonderful edible understory plant for your forest garden plantings. Tubers are freshly dug by the order. 1/2 POUND FOR $20 plus $6 priority mail.
Wikipedia says "Apios americana, sometimes called the potato bean, hopniss, Indian potato, hodoimo, America-hodoimo, American groundnut,or groundnut (but not to be confused with other plants sometimes known by the name groundnut) is a perennial vine that bears edible beans and large edible tubers. Its vine can grow to 1–6 m long, with pinnate leaves 8–15 cm long with 5–7 leaflets. The flowers are usually pink, purple, or red-brown, and are produced in dense racemes 7.5–13 cm in length. The fruit is a legume (pod) 5–13 cm long. Botanically speaking, the tubers are rhizomatous stems, not roots. Its natural range is from Southern Canada (including Ontario, Quebec, and New Brunswick) down through Florida and West as far as the border of Colorado."