Almost all new world garcinia (called rheedias before) are self pollinating and not dioecious. All old world garcinias are classified as dioecious, but in reality almost all are able to either self pollinate or produce fruit without any pollination. In other words, there are very very few (you can count them on one hand) garcinias that really need cross pollination.
It's not really known what species the plant that Whitman called charichuela is. Seems very close, or variant of, madrono.