We have both P. ambigua and P. verticillata var. ambigua, at the moment. Both are synonymized with P. verticillata in POWO: https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:692547-1#synonyms

I'm not entirely sure on these tbh

This is probably yet another case where POWO people need to be informed.

regional workers are often going to want to name everything that seems distinctive. human nature, i think. for 25+ years, i was convinced that P. ambigua & P. verticillata are different species. and maybe they are. in the field, in 25 years i never once found myself uncertain which name to apply; looking at the whole population, it always seemed easy to tell them apart... however, 5-6 years back i finally sat down with several thousand specimens from across the whole range for each, rather than just studying the mess state by state. i separated the herbarium specimens into 3 stacks, with 80% going into P. ambigua or P. verticillata piles. i set aside the remaining fifth & focused on the 2 "clear" batches. i used all the existing keys i was aware of, including the descriptions & key i wrote for the Flora North America project. and i used a nice quality dissecting scope with a micro-ruler & all the other fancy toys herbarium taxonomists play with...

and a few hours later? it became clear to me that almost every specimen had branches with flowers that matched the other species. using the whole suite of features, i.e., leaves, inflorescence details, floral details, when carefully recording the actual measurements, neither species held up as discrete & consistently separable from the other. again, this was using only the specimens that my gut-level (by sight) ID said were clearly one or the other. the brain is a pretty complex computer, capable of very subtle multi-variate analyses, and i didn't like abandoning my long-held 'belief' in there being two taxa, but i also had to accept the evidence in front of me...

i spent a couple more days going through the specimens, trying like hell to find some quantifiable distinction that actually holds up across the ranges (& not just in one small area), to no avail... i have been 'attacked' (criticized severely) by many regional botanists over the years (i first drafted the FNA treatment over 15 years ago & shared it widely long before it finally got printed), and all i can do is wish them well. go in peace, i say, and treat them however you'd like... yes, i believe that it is highly probable that Polygala verticillata in its broad sense (including P. ambigua & other infraspecific or segregate taxa) is a metaspecies complex, perhaps a stem species, out of which other lineages have evolved, lineages which may not always be morphologically diagnosable...

years back, as part of my doctoral dissertation research, i extracted DNA from several samples of 'clear' P. ambigua & P. verticillata and sequenced a handful of gene regions (ITS, trnL-F, matK, maybe rbcL?), and the phylogenetic results showed the samples to be interdigitated, i.e., they were NOT reciprocally monophyletic. so, i had already had a brief glimpse into the genetics, telling me that the lineages were not distinct. however, with only a few samples & only a few regions, maybe sampling was inadequate, maybe the lineages are relatively recent & there is just incomplete lineage sorting with those gene regions (e.g., maybe concerted evolution with ITS?), and, ultimately, if you think about most of our speciation models & the nature of population-level gene flow, it should be clear that IF species are biologically real, then we cannot (should not) enforce monophyly at the rank of species. enforcing monophyly at the rank of species is tantamount to saying that species are artificial human constructs with little or no biological reality (which may be the case, but certainly doesn't gel with how most field biologists see species)... however you analyze it, i was willing to accept that maybe the genetic markers i had studied just weren't up to the task... couple that with my inability to differentiate the taxa using measurements of herbarium specimens across their ranges, though, and i was left with two choices: 1) call myself an incompetent hack, ignore my own observations/measurements/study, and go back to accepting the views of others as my guiding light, or 2) accept that my own efforts failed to show the taxa to be distinct, no matter how much i didn't like that...

where i'm at now is mid-stream with a new project to re-address this, focusing on the P. verticillata complex in Arkansas. i see what are 'clearly' 3 species of P. verticillata here in AR... dangit... that said, we now have more than 20 samples representing all the variants, and we are using a whole genome HybSeq approach (spiked with unenriched DNA to provide chloroplast data as well as the targeted 353 single copy nuclear genes). i agree with everyone who says there should be 2 or more taxa. the problem is that the data simply don't support that. so, here's to hoping that this new approach will provide some sort of phylogenetic framework for better assessing patterns of morphological variation. maybe in another year or two, we'll be able to say something more definitive &, hopefully, more satisfactory...

Fascinating, thank you for your detailed comments!

Added deviation: https://www.inaturalist.org/taxon_framework_relationships/623245