A weed is not always simply an unwanted plant, a plant growing in the wrong place or a plant whose merits have yet to be discovered. There are those weeds that have shown, by their actions, that they are bent on World Domination. These I call the Axis of Evil (with no apologies to Dubyah).
The first offender, which goes by the nom de guerre of "the Bane of Barrington" is Buckthorn, or Rhamnus cathartica.
This nasty woody was well established when I purchased Squirrelhaven. Only by employing a Zero Tolerance policy has this bad boy been eliminated from the garden.
Fortunately, its seedlings are quite distinctive, allowing me to train the children from an early age to recognize and pull the "little bow ties."
The second arm of our Axis is a relative newcomer, but sheer seedspread has made it a serious contender for Worst Weed. It is another Alien Invader of woodlands, Garlic Mustard.
It's frothy white flowers cause it to be mistaken for a wildflower. The only good thing about it is that it is a biennial. If it can be kept from going to seed, it can eventually be eliminated.
The third arm of the Axis goes to another woody plant, but this one isn't an alien. It's a native pest, Boxelder a/k/a Manitoba Maple, or Acer negundo.
Weedy, weak-wooded trees would crowd out all other plant life if I didn't yank out each seedling, wherever it pops up.
Finally, the Darth Sidious/Emperor Palpatine of Weeds: Bindweed (Convolvulus arvensis).
On the surface it seems attractive, even friendly, with its pretty pink and white Morning Glory type flowers. But beneath the surface it extends its grasp in a stealthy ploy for expansion and ultimate World Domination. This wicked weed can't be pulled or burned. The only way to destroy it is to use a stronger evil power, the Darth Vader of weed eradication, herbicide.
These are the weeds to be feared, these are the weeds that must be stopped. A policy of appeasement will lead only to disaster. Nearly every day, throughout the growing season, vigilance must be practiced. The Fate of the World is at stake! (Okay, maybe just of the immediately surrounding neighborhood.)
Meme Alert: turn this into a meme by posting about your nastiest weeds. Win Bindweed seeds (just kidding!).
(edited 5/22/08)