The punchline would be elder flowering with groundelder

The other pic is Phlox with something growing piggyback

Epilobium

and this

Not a weed in everyone's book, but when I was battling Tradescantia seedlings, they absolutely LOVED self-sowing either right next to or right in the middle of Daylily clumps. The foliage blends right in and is easily missed when weeding. Of course when they bloom, the jig is up, but by then they're not all that easy to pull out.

Kevin

I found tradescantia growing near my compost pile yesterday and I don't even grow that plant. Must have been seeds in something I got as a trade or in some shared shredded leaves.

The last photo looks like celandine poppy which some people like. I found it self seeded too much and have been pulling them out before they can set seed.

There is a NOID plant that came along with a trade. Thought it was pretty so kept it. Big mistake as it is seeded into the lawn and amongst the other perennials.