Once more into the abyss, lol. I have collected seeds from S. mutabilis 'Henlea's Heavenly Hummingbird' and S. mutabilis 'Ruby Red Throat' that I could trade for S. microphylla.

So most of the cultivars that I have immediate access to were not distributed with species attached but I have a line of dwarf red stachytarpheta which is somewhat lining up with the microphylla description, and it's a newer introduction to cultivation lending credence to it being distinct from the previous species.

Let me know if you're still interested and we can work it out, I'm a plant breeder so all the seeds I would have are OP and could be hybrids but I can send you cuttings of the suspected Microphylla.

I've traded a lot of these, none of them for the Stachytarpheta I'm looking for, so the dwarf aspect of what you offer is attractive.

Mine are open pollinated as well. I endeavor to keep them 200 feet away from each other, which might help some, but both are mutabilis variations, so...
I overwinter plants from cuttings, but I didn't prepare enough to share.
I'll send you a treemail.