Also from the previously mentioned ARS press release, something called
spotted knapweed  (Centaurea maculosa or Centaurea biebersteinii) is
expanding incredibly fast in the the western US and Canada (see below). Is
anybody aware if this is a plant that bees forage on?

From the press release:
   "The ARS researchers' next step is to look at weed distributions and how
alien weeds have spread over time.
   "For example, spotted knapweed first entered the Pacific Northwest around
1893. The weed began to spread more rapidly in the 1950s, but distribution
exploded from 60 counties in 1985 to at least 175 counties today. The
researchers hope to identify reasons for such expansions, as well as trends
that can help identify which alien plants pose the most risk for future
expansion."