The USDA's plant database shows something like 50-ish native viola species in Pennsylvania, where I live. As far as I can tell, they're all more or less edible, but what about the flavor? Are there any especially choice species that really stand out? Internet sleuthing doesn't seem to turn up much of anything. So far, I'm getting the vague sense that purple ones generally taste better than yellow or white ones, and that short species might be sweeter than tall species.

This seems like the sort of thing that somebody somewhere must have figured out by now, since violet used to be a pretty popular flavor. The classic liqueur Creme Yvette is very specifically flavored with these obscure Italian Parma violets, which implies that they must taste somehow unique. So what about the rest of them?