Is it very aromatic? Looks like it could be the non-native pennyroyal, Mentha pulegium except the stem does not appear to be square.

Thanks esh. Those plants are along a golf course waterway, and unaccessible to non-golfers after 7:00 am. I returned there this morning, but was unable to see flower details (even with a 10x lens), because the morning dew degraded the flowers. So I dug a clump and replanted them at home. I should know in a day or two whether these plants are Mentha pulegium, or Hedeoma pulegioides. The later is more likely in our area, but usually has light blue flowers instead of the pink ones shown in the photos. The stems were square (apparently typical for both species), and crushed leaves had a strong, non-minty, somewhat unpleasant aroma. I'll post back after I check stamen numbers to confirm genus.

Thanks for pointing me in the right direction.

These plants had 2 stamens, so were likely Hedeoma pulegioides.

Since those pink flowers didn't seem to fit the possible Hedeoma species, I pressed a specimen and submitted it to our State Botanists. They suggested Clinopodia gracile (Slender Wild Mint), which isn't even in our key. Here's a little better photo of the flower. Those are hard to shoot, because they're only about 0.070 inch across when open.

Clinopodium gracile, not in your key because it is not native, I guess. Based on a few pictures on the web, it does look like that.

Thanks for the follow-up, jekeesl. It certainly looked like a mint of some type but not one I've run across.

FataMorgana

Here is a link that might be useful: USDA Plants link Clinopodium gracile