Dipladenia tenuifolia.

Botanical name: 

Dipladenia tenuifolia A. DC. Apocynaceae.

Brazil. This plant is called by the inhabitants of Sertao, Brazil, cauhy, and the tuberous root, which is the size and color of a large, black turnip-radish, is eaten by them when cooked and is said to be very palatable; in the raw state it tastes not unlike a turnip.

Sturtevant's Edible Plants of the World, 1919, was edited by U. P. Hedrick.