Whatever it is, I see millions of seeds that will be ripe any minute, if they aren't already. If all you have energy for right now is to pull/cut those off (and not leave on the ground) you would have than many fewer seeds sprouting there - and all around the area - next year. For annuals, this can help break the cycle although it can take years for all of the previously dropped seeds to get through sprouting.

Compare your plant to pics of Acalypha rhomboidea.

Really appreciate the response, purpleinopp. Yep, that looks like the culprit. Pulling/cutting these out will be my project starting tomorrow... a big one unfortunately, because there are so many of these plants in most of my flower beds. Oh well... heigh ho, heigh ho... Thanks again!

You're welcome. If this weed is covering large enough areas to bother, when you're finished pulling/cutting these, you can cover the areas with newspaper, then mulch or leaves. That should stop seedlings next year, and if it turns out that this is a similar-looking perennial, this should smother them. If they still break through, try cardboard instead of newspaper and a new cover of mulch, which is heavier than leaves. Or, of course, you could use cardboard to begin with. I just prefer paper when it will do the job since it's so much easier to work with (and to get) and molds to the contours of the soil as soon as it gets wet where the cardboard can take a few times of getting wet before it melts into place. Whatever method, you should have your space back next spring although knowing there are so many seeds there from previous years, I would probably just leave it alone until the following spring, making sure it stays well-covered.

It's a shame because it looks like there's a lot of material there, but I wouldn't want to put that stuff in my compost. I wonder if letting it turn to goop in a plastic bag would ruin the seeds and let you then put that back on the bed - the perfect revenge. Maybe someone with a confident answer will say.

Thanks again for the advice, purpleinopp, I did pull out 90% of the plants from my flower beds... it took several hours! Will wait til next spring to use newspaper and grass clippings - one of my favorites, and free. Obviously the weeds were encouraged by a couple years neglect b/c of family health challenges... Blessings!