For goodness sake - I'm trying to write something about spotted knapweed and when I go to grab the *synonyms* of it from the USDA PLANTS database, I see the taxonomists have gone and renamed it - again! I've just finally gotten down the spelling of "Centaurea biebersteinii" (in fact I just recently had to correct a couple of typos in previous ISW posts) and now I find out it has been renamed "Centaurea stoebe ssp. micranthos." Apparently it was reclassified as a subspecies back in 2001, at the "First International Knapweed Symposium of the 21st Century". This page from the ISSG database notes that the old name, Centaurea maculosa, which I quite liked, was actually misapplied, and belongs to a European species which is not found in North America.
I have a database I have built from the various U.S. state lists of banned plants. There are currently 17 different entries for the genus Centaurea, but several of them are duplicates confounded by confusion over naming, and I'm still trying to consolidate them. No wonder the field guides can't keep up.