Found this one in the prairie of central South Dakota during mid-June; I wish I had gotten better/more detailed pictures of this, because I haven't been able to find any information on it since. Thanks! -Jesse
One of the Verbenaceae. Compare with Glandularia and Lantana. Flower structure is most similar to Lantana, although I've never seen that particular colour combo before.... EDIT. Nope. Phyla nodiflora.
Nailed it. I guess the reason I couldn't find anything is because I was searching for South Dakota wildflowers, and there doesn't seem to be any record of this Phyla Nodiflora in that state. Thanks!