I think Llifle operates a lot like Wikipedia. Via volunteers. It's just specialized toward plants. I find it useful, especially in regards to hints about growing things re the size, origins and needs concerning the plants. Obviously, though, it's not the last word in authority. For the most part, folks interested enough to contribute tend to be knowledgeable to a degree. It's often a good source to find something that's a synonym that's still being used leading to the accepted name(s) currently in use. For that, I'm not sure which ones vie to be the final authority. Catalogue of Life is the one that NGA uses for current accepted official names and it may be accepted as the primary authority. Not sure though. Just contact the site directly and asking them directly would likely give you the best info.
