Tramadol has been isolated from an African medicinal plant, Nauclea latifolia. Interesting because tramadol was synthesized first, then found to be present in nature (and a known medicinal plant) later.
The rubeaceae family also contains coffee and Psychotria viridis (source of DMT in ayahuasca). Useful-to-humans chemistry seems to concentrate oddly in certain plant families, quite apart from any human eugenics; solaneacea is another good example. (Note that the compounds produced by these families are not chemically similar or necessarily the result of the same pathways - it seems like it's the abstract property of chemical utility to mammals that is shared within these families - which is why this is so unexpected.) Oddly, DMT was also synthesized before it was discovered in nature.