I use this website when i manage the lily database:
http://www.theplantlist.org/
Just enter your genus species in the search box. The next page will give some initial information. Click on the link and you see what Jovibarba sobolifera (or whatever) is a synonym for. Sometimes a bunch of links for other authoritative sites comes up at the bottom. You should check those out too because some of them may be more up to date. Play around with it!
These are authoritative sites while wikipedia is, well....
