Cuphea hyssopifolia, MEXICAN HEATHER. Joe

Agreed. If you miss some & it makes seed pods, it sounds like shooting a BB gun when mowed. If you pull it out of beds before this years' seeds fall, you should see little to none next year (as long as those BB's don't get flung back into beds from mowed area.) Break the seed cycle. The pods seem to show up within a day or two of the blooms, and ripen quickly, the sooner the better if unwanted.

Dandelion refers to plants of many different genera other than just the ones you listed. There are also a vast number of species in the 3 thistle genera you mentioned. One can't know what genus a plant is by either name (let alone species,) and within those various genera are many natives, and many exotics, for any given location. "... any of various other prickly plants." Yes, that's extremely vague, with a side of inconclusiveness, and nonspecificity. It's not getting through, but I repeat, native wildflowers are not noxious weeds. Native plants can't invade their own territory. I don't understand your objection, Kim, to advising someone to make sure the wildflowers are native. It was said this would be in a park, so there was no reason to even bring up HOA's or rows of neatly spaced annuals and perfectly mowed monocultures of non-native grass. I've seen many native wildflower gardens in various parks. It's a completely appropriate thing to do, if done well.

The plot thickens. On enlargement I really can't determine that the leaves are opposite. On the long stem on the right in the top pic they're clearly alternate but I can't even tell if that's part of the same plant. Triodonus wasn't an id it was just a vague feeling. The plant appears to be wet which also fooled me to start with. I thought the leaves were glossy but I think they're just wet. If anything the flowers look like asteraceae when blown up. Almost like an aberrant chicory.