My understanding from @whiteoak (who I hope will correct me here if I misstate anything) is that there are four different Stenanthium taxa (2 species, each with 2 varieties), three of them represented by these observations across the southeastern US. A paper in prep by Sorrie and Weakley will come out soon to clarify these 4 taxa. According to @whiteoak, my observation in the coastal plain of NC should be Stenanthium densum, as indicated by the taxon swap, but the observations elsewhere in the southeast would be one of the four different entities and definitely not all Stenanthium densum. So I hesitate to update content until the taxonomy is officially clarified, because I wouldn't want to lose any legitimate taxonomic resolution (particularly on uncommon or rare species) by lumping.