some pics of xanthochymus and the Garcinia from CATIE (Doug, not sure, but if it looks like xanthochymus, and reportedly has an acid/sweet flavor, rather than just pure acid), I'm sure it's the same plant you are talking about.
Garcinia from CATIE
GarciniaCATIE, bottom of leaf is more pale, with discreet secondary nerves, and the midrib is same color as leaf surface, pale green
Garcinia xanthochymus bottom of leaf shows secondary nerves that are less discreet, and the midrib is more yellow/green, than the leaf surface
G. xanthochymus