Oxalis can't always be removed by "pulling" as, if sufficiently established from seed, it begins to form bulbils and can both spread that way if undisturbed, or spread even faster if manually spread by digging over the soil without capturing them. If your "pulled" plants re-emerge then it would be worthwhile digging up all the soil after your worthwhile plants are finished, and lifting a pocket of soil containing and around the oxalis to capture the bulbils. Don;t compost - bag it in a bin. The commelina spreads by anchoring roots and can re-shoot from a miniscule bit. Once again, try to carefully lever out every rooted piece, not leaving any stems to fall back on the ground, and completely destroy what you have gathered.

The tree looks similar to the invasive Chinese Tallow Tree (Triadica sebifera). Take a look at this link for further identification. If it is a tallow, you might want to consider getting rid of it before you and your neighbors develop a Tallow-tree jungle! Here is a link that might be useful: Invasive Species Tallow-tree

Yea, I'm guessing that dead stem belongs to the plant as a winter leftover... And I have seen some Ruellias "around" here, so Ruellia humilis (Prairie Petunia) is probably a good guess, thanks!!!

Each leaf has 3 leaflets. I don't have a clue, but only thing I've seen like that is wafer ash, and I doubt that's it (wafer ash is quite rare).