Lepidium meyenii (Maca), grows in the central Andes of Peru at altitudes between 4000 and 4500 m and it has been proved to be effective in improving sexual desire in men , and sexual behavior in male rats and mice .
Córdova A, Vega K et al.  conducted a 12-week study in order to evaluate the effects of Maca, at doses of 1,5 g or 3,0 g, on sexual desire in healthy men. Data obtained at 4, 8 and 12 weeks of Maca administration showed improved sexual desire as compared with placebo at 8 and 12 weeks of treatment.
Authors of “Effect of Lepidium meyenii (Maca), a root with aphrodisiac and fertility-enhancing properties, on serum reproductive hormone levels in adult healthy men” tested men aged between 21 and 56 years who received 1500 mg or 3000 mg of Maca. Data showed that compared with placebo, Maca had no effect on any of the hormones studied nor did the hormones show any changes over time. Multiple regression analysis showed that serum testosterone levels were not affected by treatment with Maca at any of the times studied (P, not significant).
Gonzales, G. F., et al. “Effect of Lepidium meyenii (Maca), a root with aphrodisiac and fertility-enhancing properties, on serum reproductive hormone levels in adult healthy men.” Journal of Endocrinology 176.1 (2003): 163-168.
Zheng, Bo Lin, et al. “Effect of a lipidic extract from Lepidium meyenii on sexual behavior in mice and rats.” Urology 55.4 (2000): 598-602.