The leaves remind me of Virginia bluebells (Mertensia virginica), but mine show up in Spring and disappear after blooming.

Thank you! As these have popped during our very hottest weather, it's unlikely to be M. virginica.

Also Virginia Bluebells do not have opposite foliage. They look a bit shrubby. Could they be suckers?

Thanks, floral_UK. I don't have any shrubs nearby (or even not so nearby) that resembles this. And they're popping up too far away from either of my neighbor's fences to be coming from them. I also know what's on their side(s), and it doesn't look familiar.

I know I am wrong, but it reminds me of my sage.

TY, Margaritaville. If you're referring to common sage (the herb?), these leaves don't have any of the texturing sage does -- completely smooth.

Check for milky sap. I have my suspicions.

Someone locally thought it might be A. viridis milkweed, which I do have growing in this bed. I checked for sap the other day: nada. I see new growth on my A. viridis every spring, and these leaves don't look similar -- esp as they progress.

Well, that blows my theory. I was leaning toward Asclepias syriaca. But on second look, the venation isn't correct for that. Back to the drawing board, lol.

Thanks anyway, fig_insanity!

@phoenix7801: Thyrallis is a definite maybe/probably! I did have one of these plants (at the opposite end of the yard) here last year, so seeds may have floated over. How odd that they took this long to germinate, and all at the same time.

I grabbed a pic (rt.) off the internet -- do you still think this is a match? It's the shape of my circled leaf that's throwing me. Thanks!

Galphimia glauca, (Thryalis), can have slight leaf variation.

Thanks, Jay!