I've done the image search online, Wikipedia, and the like, but here it is all in one place.
Now, if I understood some of the terminology better (had to look up petiole, ochrea), the search function would probably cut my selection down to just a few, as there are 16 different characteristics to identify your weeds by. And when you open each file, there is more than one picture, showing different stages in the weeds life-cycle, along with more information about the weed than you probably wanted to know, unless you are a botanist.
The only thing it doesn't tell you is how to control or eradicate the weed, but the name of the app is ID weeds, not exterminate them.
One of my problems with the app was that some of the IDs involve pulling the weed, and I planted a wildflower seed garden, and wanted to know whether something I couldn't identify yet (no flowers yet) was something I planted or a weed.
The only reason I didn't give it 5 stars is that:
a) the thumbnails for their weed guesses are tiny, so you often have to open them all up. If they were a little larger, or zoomable (or enlarged when you hovered over them), you could save the time of opening and closing each file.
And
b) the first picture in each file I looked at wasn't always a close up of a mature (or at least identifiable) plant. Sometimes you had to go 3 or more pictures in to see what the plant looks like when you're likely to be pulling it.
I'd really like to give 4.5 stars, as that's not a deal breaker, just gives them something to shoot for on the next version.