You can look up weeds with images for most states and provinces at the
Ergonica Weed Identification Reference Matrix (EWIRM). There are over
200 lists with common and scientific names and often images, as well,
on this site. Just about every weed image database on the web and also
references you can purchase in book form or disks is included.
Some of these online references and disks allow you to select the
features of your suspect plants and narrow down the selection to only a
few that you can view with images for a positive identification.
It's true that any plant can be a weed, but the reverse is also true,
that is, we can redeem our weeds if we identify their value.
Best of luck in your weed / plant identification quest.
Know your weeds to control your weeds www.ergonica.com