Eve Emshwiller sets Between the Lines straight on this whole oca thing:
The Andean tuber that has an effect on testosterone is not oca, Oxalis tuberosa, but another Andean tuber that looks even more like oca than potatoes do: Tropaeolum tuberosum, which has several common names in different parts of the Andes, such as mashua, añu, and isañu.
So many Andean roots and tubers, so little time…