I wish I had more to offer about this intriguing little tidbit, but the Internets are not cooperating. Apparently:
Tourists visiting Chile's picturesque port town of Valparaiso have cleaned the town out of a herbal aphrodisiac called palwen, an indigenous remedy also known as "Mapuche viagra," according to local media.
"The Mapuche Viagra increases the desire, the libido and the sexual appetites of men and women," Italo Diaz, a pharmacist at the Mapuche pharmacy Makelawen, told Reuters. "The compound is a Mapuche secret."
Which explains why there's no palwen vault on Erowid. Still, how much of this is just adroit sales tactics and how much is legitimate aphrodisiac goodness? I guess unless you've been to Chile, you'll never really know...