The Plant List is the largest, most exhaustive listing of plants in the world's history. In fact, it is a list of every single known plant on earth, over a million. And it's all available in one place online to anyone, not just academics.
The Royal Botanic Gardens and the Missouri Botanical Garden are the prime movers in this attempt to sort what Discovery News called the "taxonomic jumble" of plant names that has grown up around the study of botany.
The Plant List brought together scores of databases and lists from scores of institutions into one place and standardized most, identifying those whose naming is still a matter of discussion.
Experts still do not agree on between 200,000 and 300,000 of the names. The role of botanists in the next 9 years, when the database is due to be "finished" is to reduce that number to zero.
If there's a fault in the list, it's an ironic one. It's more difficult to find things, either via search or browse, than it ought to be. When I searched on the genus "rosa" the result was a statement that the genus was not available. When I browsed, allowing the titanic list of genera load (which took several minutes), I found it.