What your describing sounds like Parrots Feather, Anacharis/elodea, Cabomba or hornwort. They are all invasive.

It's a little trickier than most broad leaved weeds but I still wouldn't rank it as the worst. Not at all. In a lawn: the best is something containing triclopyr: there are "homeowner" formulations out there, in the big box stores, that are a little weak and use the amine. I'm pretty sure the current version of "Weed B Gone" is tc amine. At the very least add a few drops of dishwashing detergent, because I think they skimp on the surfactant, and use the strongest dilution recommended. It is best to do it in the fall, but it might have seeded at that point, second best is spring, summer is the worst because I think it goes semi-dormant. I personally used a triclopyr ester in the fall and got complete kill of huge patches. A "3 way" formulation works too, albeit not quite as well as triclopyr so I wouldn't bother. Crossbow would work but again that's a "professional" product and I wouldn't recommend it unless you can handle using those. Just in a bed? Use a strong dilution of glyphosate, again, with enough surfactant to completely wet the leaves. Trust me, if applied correctly, it will die. Maybe not until 10 days later, though. When you're done with the glyphosate, please don't drink it or use it as a cocktail mixer. It might 'cause cancer': just as dairy (even organic), red meat, alcohol, or refined sugar might. I just spot treated some tiny areas of it with triclopyr ester, but this late in the season you have to be very careful about the vapors hitting nearby plants if you dealing with it near an ornamental bed. I once got into a bit a trouble with a huge area-wide application of tc ester to kill charlie and violets: we had an inversion that night, totally still air which is very unusual here, and fog formation. The vapor hung in the air and somewhat burnt the foliage of a Cedrus 'Shalimar' and a couple other ornamentals. They survived but it was a learning experience. Nothing would have happened if there had been some wind that night. I share the story to say: be careful with ester formulations. But, violets and charlie are completely gone from the main part of my lawn. (the spot treatment I mentioned was for a side area of grass, near ornamental beds, where I didn't want to use my ATV sprayer)

I've got it all over. It is a type of vetch - not either of the crown vetches, as the flower is a vivid purple - but I can't now remember what, nor where I looked to find out. Try a local wildflower book, if you can't find it elsewhere, as it is a commonly growing plant. It's a royal pain, not least because it very easily breaks off from the roots when you pull at it, so the roots stay to resprout! It sends tendrils all over the place, and can, if really healthy, start to smother small plants. Because it IS sort of lacy, it won't do too much damage to larger plants, except entwine itself through them.

Gang, I had this looked at by an arborist on Saturday and he indicated it is part of the root system from a poplar tree I cut down (last year or earlier this year, I can't remember). The recommendation is to grind the stump and poison the root system. That should go a long way to helping with this situation. Thanks again to everyone who chimed in on this thread. I really appreciate it. Bill