A few years ago I wrote a little webscraper to collect taxonomic treatments from the Flora of North America website. There were a few problems with the last version, as the webpages on the FNA site have some inconsistencies that my code didn’t handle. Checking the key against the list maintained by the Natural Heritage Information Center, there were about 25 species missing, plus the entire genus Cyperus. I added the missing species, so the key should now be complete. It’s available on my botany page. The source files are available on my bitbucket account.
Ball, Peter W., Reznicek, A. A., and Murray, David F. 2002. Flora of North America. Volume 23: Cyperaceae. Oxford University Press.