thanks to all that replied; yes it is giant or great ragweed, Ambrosia trifida - I actually had another photo but that specimen was by itself and was in flower and the photo here is from a huge stand of the plant running several hundred feet along the creek, but there is no mistaking the leaf shape

WELL...last night someone on name that plant forum indicated that it was called Yellowrocket, which led to finding that it is probably a very close relative of Yellowrocket: Wild Radish. Whis is a very close relative to Wild Mustard :-) The only reason it can't be Yellowrocket is because the stems and leaves have tiny hairs, which indicates it is Wild Radish. However. I have seen pics of Wild Radish now on Google Images that don't look like this plant, and some that show Yellowrocket looking dead-on accurate, save for the leaves. Ha. At any rate, I'm pulling them up...tis' not to be... Thanks so much for your help, timbu and fammsimm. Now I am also familiar with two other kinds of weeds, so if I spot them, I'll know right away :-) Joanna

Not sure. Maybe some kind of wild lettuce?

Got some other responses and I think it's a West Indian Nightshade (Solanum ptycanthum dunal). The description - including size - and pictures match perfectly. Yep, it's considered a noxious weed, but so are some other plants used in wildlife gardening. Reports of toxicity are varied but all seem to agree that a considerable amount of the berries and/or plant itself would have to be consumed to cause serious harm. I don't have to worry about children accidentally eating any of the berries, my yard is fenced and locked, and since the plant doesn't grow very large, I may try starting a few from seed since the mockingbirds appear to love the berries. Everything I plant is for the birds or butterflies; had to get rid of the grape vines since the only things eating the grapes were possums and my dogs. After relocating a litter of 7 "teenage" possums and realizing I would never keep my dogs and the grapes apart (grapes and raisins are very toxic to dogs), I reluctantly had my vines relocated to someone else's yard. Thanks again - if I see any Chinaberrys, now I'll know what they look like! Gretchen