In article says...
You can investigate more species with several interactive weed
identification references that allow you to select by plant features.
Over 200 weed and plant identification references are listed by region
at the World of Weeds at www.ergonica.com.

Although useful, that ergonica.com is a rather obnoxious site using the
top half of the screen for their banner making it difficult to navigate.
They did have some useful links however. I was searching and searching
for a weed id tool and they had a link to it at:

http://web.aces.uiuc.edu/weedid/